CA1167298A - Rear projection screen - Google Patents
Rear projection screenInfo
- Publication number
- CA1167298A CA1167298A CA000390002A CA390002A CA1167298A CA 1167298 A CA1167298 A CA 1167298A CA 000390002 A CA000390002 A CA 000390002A CA 390002 A CA390002 A CA 390002A CA 1167298 A CA1167298 A CA 1167298A
- Authority
- CA
- Canada
- Prior art keywords
- screen
- axis
- lenticules
- lenticule
- light
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B21/00—Projectors or projection-type viewers; Accessories therefor
- G03B21/54—Accessories
- G03B21/56—Projection screens
- G03B21/60—Projection screens characterised by the nature of the surface
- G03B21/62—Translucent screens
- G03B21/625—Lenticular translucent screens
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Overhead Projectors And Projection Screens (AREA)
- Transforming Electric Information Into Light Information (AREA)
Abstract
ABSTRACT
A single-sheet (i.e. two-surface) rear projection screen for television applications is described, in which the front or viewer-facing surface is formed with vertically running lenticules for horizontal image light distribution and the rear or projector-facing surface is formed with horizontally running lenticules for vertical image light distribution. There is no need for a diffuser. The lenticule profiles on both surfaces vary as a function of distance from the projection axis in a manner calculated to accomplish several optical objectives: collimation, cosine power fall-off compensation, and rearward reflection gradient compensation. Computer programs for calculating the profiles are disclosed.
A single-sheet (i.e. two-surface) rear projection screen for television applications is described, in which the front or viewer-facing surface is formed with vertically running lenticules for horizontal image light distribution and the rear or projector-facing surface is formed with horizontally running lenticules for vertical image light distribution. There is no need for a diffuser. The lenticule profiles on both surfaces vary as a function of distance from the projection axis in a manner calculated to accomplish several optical objectives: collimation, cosine power fall-off compensation, and rearward reflection gradient compensation. Computer programs for calculating the profiles are disclosed.
Description
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REAR PROJECTION SCREEN
This invention relates to image projection screens, such as may be llsed for projection television systems.
It is particularly directed to a screen of the rear projection typ~ which is compensated for reflection losses.
Background and Summary of the Invention Image projection systems are employed for a number of applications, including large-screen television. Rear projection systems are those in which the image is projected on the rear surface of the screen, the screen is formed of translucent or transparent material, and the image is therefore visible through the screen to observers located on the front side. Such systems are often preferred for projection TV applications, because they permit the projectors and associated optics to be hidden behind the - ~ screen. A disadvantage of the rear projection designj-- -;~ ~ however, is that some of the image light is not transmitted forwardly through the screen, but instead is lost due to rearvard reflection from the front and rear surfaces of the screen.
More importantly, the fraction of the total image light which is reaxwardly reflected is greater at greatex distances from the axis of the projection system. Thus, even if the overall brightness is raised to compensate for reflection losses, the brightness will still be non-unifoxm; it will decrease from the axis to all four edges :: ~
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Docket 999 7 2 ~ ~3 of the screen. Consequently, at any given viewing location an observer will find the TV picture to be brighter in the center than it i5 elsewhere. This invention aims to compensate for such non-uniformity.
It is common for projection screens to employ lenticular lenses for optical processing of the image projected thereon~
These are parallel arrays of ridges formed in the surface of the ~creen, which have light-refracting cross-sectionAl shapes. Each individual ridge, or lenticule, refracts only a small portion of the image; but the array as a whole processes the entire image.
ln the past ~uch lenses have been formed in rectilinear arrays ~nd used for distributing the image light over a selected range, vertical or horizonkal; so that observers at different heights, or at different azimuths relative -to the screen, can all view the ~ , .
same projected image. Prior art screens have also used circular or spiral lenticular arrays, called Fresnel lenses, as "field"
lense~ for collimating the image light, which arrives in the form of divergent rays.
Some prior ar~ projection screens comprise two or more 20 ~ sheets of material, and thus have at least four sur~aces (two .
orwardlv facing and two rearwardly facing) on which to place such lentLcular arrays. Other prior art screen designs employ only one sheet (or the equivalent, a plurality of sheets bonded `Eace-to-face). Multl-sheet screens are more expensive to manu-facture, and they are more prone -to re~lections which degrade performance. These include rearward reflections which cut down ., Dn transmitted light, as well as ~orward reflections of ambient light which reduce contrast.
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REAR PROJECTION SCREEN
This invention relates to image projection screens, such as may be llsed for projection television systems.
It is particularly directed to a screen of the rear projection typ~ which is compensated for reflection losses.
Background and Summary of the Invention Image projection systems are employed for a number of applications, including large-screen television. Rear projection systems are those in which the image is projected on the rear surface of the screen, the screen is formed of translucent or transparent material, and the image is therefore visible through the screen to observers located on the front side. Such systems are often preferred for projection TV applications, because they permit the projectors and associated optics to be hidden behind the - ~ screen. A disadvantage of the rear projection designj-- -;~ ~ however, is that some of the image light is not transmitted forwardly through the screen, but instead is lost due to rearvard reflection from the front and rear surfaces of the screen.
More importantly, the fraction of the total image light which is reaxwardly reflected is greater at greatex distances from the axis of the projection system. Thus, even if the overall brightness is raised to compensate for reflection losses, the brightness will still be non-unifoxm; it will decrease from the axis to all four edges :: ~
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Docket 999 7 2 ~ ~3 of the screen. Consequently, at any given viewing location an observer will find the TV picture to be brighter in the center than it i5 elsewhere. This invention aims to compensate for such non-uniformity.
It is common for projection screens to employ lenticular lenses for optical processing of the image projected thereon~
These are parallel arrays of ridges formed in the surface of the ~creen, which have light-refracting cross-sectionAl shapes. Each individual ridge, or lenticule, refracts only a small portion of the image; but the array as a whole processes the entire image.
ln the past ~uch lenses have been formed in rectilinear arrays ~nd used for distributing the image light over a selected range, vertical or horizonkal; so that observers at different heights, or at different azimuths relative -to the screen, can all view the ~ , .
same projected image. Prior art screens have also used circular or spiral lenticular arrays, called Fresnel lenses, as "field"
lense~ for collimating the image light, which arrives in the form of divergent rays.
Some prior ar~ projection screens comprise two or more 20 ~ sheets of material, and thus have at least four sur~aces (two .
orwardlv facing and two rearwardly facing) on which to place such lentLcular arrays. Other prior art screen designs employ only one sheet (or the equivalent, a plurality of sheets bonded `Eace-to-face). Multl-sheet screens are more expensive to manu-facture, and they are more prone -to re~lections which degrade performance. These include rearward reflections which cut down ., Dn transmitted light, as well as ~orward reflections of ambient light which reduce contrast.
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t Docket 999 1 16~9~3 Single sheet screens are leqs expensive and le~s rPflective, but the design constraints are more severe because they have only two surfaces on which k place lenticular arrays.
Some oE the single sheet designs have a Fresnel ield lens on one side for collimation, and a vertical rectilinear lenticular array on the other side for horizontal distri-bution. Sincethat takes up all the available surfacPs, ~creens of thiq type often rely upon a light~diffusing ti.e. translucent rather than transparent) layer to sprPad the image light vertically.
. The use of diffusion for this purpose, however, has its disadvantages. ~iffusion hy i~s nature cannot be confined to the vertical direction, and so it affects the distribution of light in the horiæontal direction as well.
Diffusion is also a less efficient method of image,light distribut.ion than re~raction, owing to the significant amount of backward reflection, and also some absorption, attributable to the diffusion layer. In addition'ambient light is reflected hack to the viewer degrading contrast. ~Xe amount of d.iEfusion which occurs is. also diffieult to eontrol.
If the diffusion element is applied as a surface co~ting, uniform thickness is difficult to achieve. Such ::~ coatings also tend to fill in the valleys between the ridges of a lenticular array. If diffusion is achieved by molding the screen with a rough surface texture, then the mold must be carefully maintained ~o preserve its surface characteristics over a large number of pressings.
Furthermore, some of the resin may adhere to the rough surface of the mold, which reduces the ability of the ~creen to diffuse light, and also makes its removal from the ~ld mor~ difficult. Another appro;ch to diffusion is the use -'' of light-dispersing pigment granules or other optically active particles mixed with the screen resin before pressing.
It is important, when using this approach, to make sure that the diffusion material is dis-tributed uniformly across the screen, or non-uniform brightness distributions may occur, causing poor image quality. On the other hand, if the diffusion material is distributed throughout the thickness of the screen, as is usually the case, the focal -plane of the projected image is not distinct, which results in loss of image sharpness. Another problem is that the presence of the diffusion material may affect the molding and handling characteristics of the resin.
The present invention relates to a projection screen for use with projection means located rearwardly of the screen for displaying an image to a plurality of observers located at viewing positions which are on the front side of the screen and dispersed in a direction parallel to the screen; the projection means defining an axis; the screen including at least one array of substantially rectilinear lenticuies having respective light-refracting cross-sectional shapes adapted to redirect light arriving from the rear side of the screen so that an image formed on the screen by the light is visible at the dispersed positionsj the .
respective cross-sectional shapes of the lenticules varying as a function of their distance from the axis in such manner that, for each position within a selected angular viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from the axis than is directed to that viewing position from those lenticules which are closer to the axis, so as to at least partially compensate for the lmage light rearward reflection loss gradient; the lenticule cross-sectional shapes being defined by a succession of mg~o ~ ~ ~
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lenti.cule profile elements; the slope angle, lengtll and position of each of the len-ticu]e profile elements ~eing determined by an algori-thm which calculates the light transmission provided by each of the lenticule profile elements, and adjusts the slope angles, lengths and positions thereof to achieve the reflection loss gradient compensation.
In its method aspect, the invention relates to a method of manufacturing a projection screen for use with projection means located rearwardly of the screen for disp].aying an image to a plurality of observers located at viewing positions which are on the front side of the screen and dispersed in a direction parallel to the screen;
the projection means defining an axis; the screen including at least one array of substantially rectilinear lenticules having respective light~refracting cross-sectional shapes adapted to redirect light arriving from the rear side of the screen so that an image formed on -the screen by the light is visible at the dispersed positions;the respective cross-sectional shapes of the lenticules varying as a function of their distance from the axis in such manner thatj for each position withi.n a selected angular viewing range, a greater Eraction of the ,incident image light is directed to that viewlng position from those lenticules which are further from the axis than is directed to that ~: :
~ :viewing position from those lenticules which are closer : :
to the axis, so as to at least partially compensate for the image light rearward reflection loss gradient; the lenticule cross-sectional shapes being defined by a 30~ succ~ession of lenticule profile elements; the method comprising the steps of: calcuLati,ng the light transmission provided by each of the lenticule profile elements; and adjusting the slope angle, length and position of each ,~`
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of the lenticu]e profile elements in a manner to alterthe light -transmission to achieve the reflection loss gradient compensation.
Thus, the present invention contemplates a single-sheet ~or two-surface) screen design which does not employ diffusion for vertical distribution. It employs a fully transparent, non-diffusive material which is formed into a sheet having a vertically running, horizontally dispersing rectilinear lenticular array on one surface, and a horizontally running, vertically dispersing rectilinear lenticular array on the other surface. Since there is no other surface left on which to form a field lens, the collimating function is built into the refractive characteristics of the two lenticular lenses. Since the angle of incidence of the image light varies from 0~ at the axis of the projection system to progressively larger angles with increasing distance from the axis, the collimating function requires the refractive properties of the lenticules to vary as a function of screen position.
20 ~ Hence their cross-sectional shape changes from lenticule to lenticule across the surface of the screen.
Change of lenticule shape as a function of .
screen coordinate was employed by the prior art for thls purpase~in a number of spiral or circular Fresnel field lens ~ : :
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mg/~o - 4b -:, , Docket 999 designs and also in some rectilinear lenticular arrays. Some prior art rectilinear lenticular arrays also change the lenticule cross-sectional shape as a function of screen coordinate for another purpose, i.e., in order to compensate for the cosine power fall-off in image light intensity as a function of angle of ray divergence, which results from the inherent characteristics of the projector focussing lenses.
It appears, however, that no prior art screen varies the lenticule cross~sectional shape as a function of screen coordinate in a manner to compensate even partially for the fact that the reflection losses are greaker at greater distances from . . .
the projection axis. It is especially important to do this in a ~creen of the present type, because thé use of two orthogonal distributive lenticular arrays would otherwise produce unacceptable brightness gradients in both the vertical and hori-zontal directions due to the reflection differential across the height and width of ~he screen.
The problem of reflection loss gradient has been recog~
nized in Strong et al., U. S. Patent No. 2,200,646. That ~0 reférence, however, is not concerned with one or more angular ranges of viewing positions. It is only concerned with a linear range of viewing positions extending along the axis~ with only tha perpendicular distance from the screen as a variable para-meter. In Strong the projected image is used only as a cinema backdrop, and thus there is only one "observer", i.e., a movie camera which is always set up in some axial position, rather than a plurality of ~npredictable human observers who may take viewing positions above, below, or to either side of the axis. Therefore, -5~
~ Docket 999 I 1 ~72~
the brightne~s gradient i5 eliminated only for axial viewing positions at various perpendicular distances ~rom the screen. No compensa~ion i5 provided or a range o~ off-axis viewing positions dispersed in any direction parallel to the screen, such as horizontally and vertically.
If that screen design were used in a projection TV system, all viewers would have to take up single-file positions directly on the axis, otherwise the brigh~ness of the pro-jected image-would vary vertically or horizontally or both.
Moreove~, the Strong patent uses the same lenti-cule cross-sectional shap`e at each location. The limited degree of compensation for differential reflection which ; ~ is described in ~h~ patent results solely from th~ fact that the light reaching a given axial viewing position, from any two lenticules having different screen coordinates, læ refracted ~rom different facets of the lenticule pro-fileO Thus, no use is made of the concept of lenticule ' shape change for the purpose of compensating reflection `-' differentials. ~ , In the present invention, the lenticules vary as a \ - -function o screen coordinate in such manner that reflection ;-differentials are at least partly compensated for each one of a selected range of viewing positions extending in at least one direction parallel to the screen, ~ , vertically and/or ~orizontally. The variation is such that, for each viewing position within the selected hori ontal and/or vertical viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from the axis than is dlrected to that viewing position from -those lenticules which are closer to the axis.
Docket 999 9 ~
This compensates at least partially for the gxeatex image light loss due to rearward reflection ~uffered by those lenticules which are further from the axis, as compared to those lenticules which are closer to the axis.
In the preferred form of the invention, both the vertical and horizontal lenticular arrays are so compen-sated. Thus, at any viewer position within a selected horizontal viewing angle and a selected vertical viewing anyle, the observer willsee a projected image field which is uniform in brightness from top to bottom and from left to right.
The foregoing background discussion;and brief description of the invention, as well as its features and advantages, will be more fully understood by reference to the following detailed description of the preferred .
embodiment of the invention, when read in conjunction with the following drawings.
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- Brief Description ~2~0 of the Drawin~s Fig. 1 lS a top plan view, schematic in nature, j~ ; of a rear projectlon system employing a lenticular screen n accordance with this invention.
Fig. 2 is a side elevational view, schematic in na~ure, of the same projection system.
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Fi.g. 3 is a perspective view of a f~agmen-t of a single-slleet rear projection screen which is employed in the projection system of Figs. 1 and 2, and which has respective lenticular arrays on opposite faces thereof.
Fig. 4. is in the nature of a horizontal cross-section, and shows the light refracting cross~sectlonal profiles of an incomplete but representative number of lenticules se].ected from a vertically extending, horizontally distributing array formed on the front 1.~ (viewer) side of the rear projection screen of Figs.
1 through 3~
Fig. 5 is in the nature of a vertical cross-section, and shows the light-refracti.ng cross-sectional profiles of an incomplete but representat.ive number of lenticules selected from a horizontally extending, vertically distributing array formed Oll the rear (projector) side of the rear projection screen of Figs. 1 through 3.
Fig. 6 is a flow ehart summarizing a computer program for calculating the profiles of the lenticules on the proieetor slde of the lenticular sereen of this inventionO
Fig. 7 is a flow ehart summarizing a computer ;: program for ealculating the profiles of the lentieules :
- ~ ~ on the ~iewer side of the lentieular sereen of this invention.
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F:L9S. 1, 2 and 3 are intended to represellt the invention in a qualitative fashion only, as patent drawings usually do, and therefore are not dra~n -to scale.
Figs. 4 and 5, on the other han.d, which are profile diagrams of screen lenticules used in Figs through 3, are drawn substantially to scale in order to represent quantitatively, and wi-th precision, a typical sequence of lenticule cross-sectional shapes i.n accordance with this invention. Scales are provided in inches along the axes of these drawings, and the specific dimensions indicated are for a particular embodiment of the invention which is preferred. The illustrated proiles exemplify the nature of the changes in the cross-sectional shapes of the lenticules across -the screen, and also the rates of such changes, for a particular set of screen dimensions ana a particular set of enyineering objectives and design parametars;
but the scope of protecti.on to be afforded thi.s invention ;~20 of course extends to any set of design conditlons.
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~ocket 999 I ~ ~72~
Detailed Description of the Preferred Embodiment ~ ~ O -As seen in Figs. 1 through 3, an upright rear projection screen 10 in accordance with this inventiQn preEerably comprise~
a single sheet 11 formed of plastic material by any conventional process, such a compression-molding, casting~ or roller extrusion.
The invention, however, could just as well be used with two or more such sheets bonded together face-to-face in order to form a unitary str.ucture having only one foxward facing surface and one rearward acing surface, because in that case the bonded sheet would in effect have only two air inter~aces at which undesirable forward ox rearward reflec~ions can take ~lace.
The invention could be applied to multiple sheet screen designs .
also~ but that would not be preferable because then there would be four or more air interfaces at which reflection losses could occur. ~ ~
Any of the conventional light-transmitting polymers which are ordinarlly used in the art to Porm rear projection screens will be satisfactory for this purpose; but, since diffusion is not relied on for light distribution in this invention, best results will be obtained~with a fully ~xansparent material having 20~ no~plgment granu~es or other optically active substances incor-porated~therein. It also~follows that the suxface of the sheet 10 sho~Id be smooth (untextured~ on a ~ublenticular scale, and no~dif~usion coatin~ should be employed. But the invention, if :
desired~ may be employed with an opaque dark coating (not shown) ; distribu~ed, in a pattern known to~the art, so as to form a black surround to reduce the reflection o~ am~ient light incident UpQn the front (viewer) surface of the screen, and thus improve the contrast (or optical signal-to-noise ratio).
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--10-- , ,: , ' , , Docket 999 I ~ ~7298 A projector 16 on the rear side of the screen 10 has a generally horizontal optical axis17, which inter-~ects the screen at an axial point designated 0,0 because lt forms the origin of a system of x, y rectangular coor-dinates useful or designating lenticule positions on either side of the screen lQ. Normally, but not necessarily, the projection system would be arranged so that the origin is at the geometric center of the screen. The rectangular coordinates of which we will speak are oriented horizontally (x) and vertically (y) respectivel~, and both of them .~
numerically increase in ~ositive and ne-~ative directions from the origin as is conventional.
The sheet 11 has only two ~urfaces avail~ble on which to form lenticular arrays: a front surface 12 facing viewers A through F, and a rear surface 14 facing projector 16. A-vertically~running array 18 of parallel rectilineax lenticules 18.1, 18.2, etc. is formed on the front screen surface 12 for the purpose of horizontally distrihuting the~image light supplied by projector 16 20~ ` to viewers A, B, a~ndC who are at locations dispersed horizontally over a range~extending~to both sides of axis~17; i.e., these viewers are seated at different azimuth p~ositions relative to screen 10. A horizontally running array 20 of parallel rectilinear lenticules 20.1, 20.2, .
etc.-is formed on~the rear surface 14 for the purpose of vertically distributing the image light supplied by projec~or 16~to viewers D, E, and F who are a~ locations dispersed vertically over a~range extending both above and below axis 17; ~ , these viewers are people of different sizes : ' .
~ sitting in chairs of different heights located at different -Docket 999 ~
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distances from the screen. The lenticules may be conveniently formed by compression molding, as is conventional in the art.
The use of such lenticular arrays for vertical and/or horizontal distribution of image light is old, as i5 the concept of a scxeen comprising a single sheet.
The range of horizontal light distribution exceeds the range o~ vertical distribution,because there is not as mu~h angular difference vertically between the heads of .
seated viewers as there is horizontally between chair locations.
It is an inherent ~roperty of pro~ection screens that the - overall brightness o-f a projected image has a profile which un-avoidably decreases with increasing angle of view, relative to the screen axis, in the vertical and horizontal directions.
Conventionally, the useful angular range is arbitrarily-defined as that which is bounded by the half-brightness fall-off angles.
In a typical design the vertical half-brightness fall-off need only be of the order of 8 above and below the axis, whereas the horizontal half-brightness fa~l-off should be of the order of 22.5 leEt and right of the axis in order to optimize viewer ~20 ~ocatLons and screen brightnes6.
Since the angular range of vertical distribution is the smaller of the two, the horizontally running, vertically di~-tributing array 20 has less re-entrant groove area. Preferably, ~ ~ ~ then, lenti~cule array 20 is chosen to ~e located on the rear sur-;~ face 14 so as to minimize the rearward reflection of image light from re-entrant areas. The black surround coating, if used, is located on the ront surface, which permit~ the use of a thlcker and therefore stronger screen, and allows a grea~er thickness ; tolerance and a grea1ter tolerance for inaccuracies in the deposi-tion pattern of the black coating. This is because the coating _ / c;? _ Docket 999 . :
ha~ gaps which mus~ be located at the foci of the opposite lenticules 20, and these foci are smaller and/or can be located further from the lenticules 2p when the latter have a smaller angular light spread.
It is old in this art to vary the light-refracting ¢ross-sectional shapes of lenticules 18,1, 18.2, etc. and/or 20 1, 20.2, etc. for certain purposes as a function of the ~istance of the lenticules from origin 0;,0. Thus, image rays such as 22 which s~rike at or near the horizontal extreme~ of the screen 10 have a larger angle of incidence ~ measured .. . . ... ~ . . - ~ . - , -relative to a screen-normal line 28, than those rays which strike at or near the axis 17. The same may be said or rays 24 which strike at or near the vertical extremes. The ~rior art, accordingly, varied-the light-refracting cross~sectional shapes of these lenticules as a ~unction of horizontal and vertical ~creen~coordinates so as to refract the image rays more at screen locations more distant ~rom the origin, and less at screen .
locations less ~istant from the origin. This serves to collimate the lmage rays without the need for a separate field lens ~20 ~ such a circular or spiral Fresnel, an important consideration in a single-sheet screen deslgn which has no room ~; for a separate field lens. The present invention, in oommon with the prior art, varies the lenticule pro~iles in arrays 18 and 20 in this manner and for this purpose.
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Docket 999 ~ 1 ~7298 Additionally, any off-axis ray (such as 22 and 24) suffers a loss in intensity which is ~ function of a power of the cosine of the diveryence angle 0 between that ray and the axis 17, a fact which results rom the inherent characteristics of the focussing lens assembly 26 of pro- ~
jector 16. The prior art has compensated for this efect hy varying the shape of the lenticules as a function of vertical and/or horizontal s~reen coordinate so that more image li~ht is refractedto any given viewer position by those lenticules 18 or 20 which are further away from the axis 17 than is rerac-ted thereto by those lenticules 18 or .
20 which are closer to the axis. In common with the prior art, this invention also varies the lenticule shapes in both arrays or -this purpose.
As recognized in the Strong patent, there is yet another pararneter which varies as a unction of screen coordinate. The rays (such as 22 and 24) which are further from the axis 17 have a higher angle of in~idence ~ than those nearer the axis, and as a result the fraction of the imag~ light which is lost because of backward reflection from the air interEaces (front and back surfaces 12 and 14 of the sheet 11~ is gre~tex as distance from the axis 17 increases.
If this is uncorre~ted, an observer at any viewing position will notice that the projected image is brighter at the center of screen 10 (origin 0,0) ~han it is at any location above, below or on either side thereo. Even if the compensation scheme of Strong et al. is employed, the same problem is encountered for all viewing positions which are off-axis.
Strong, as noted, does not suggest changing the lenticule --1'1-- ~
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profile as a function of screen coordinate, and uses a con-stant lenticule profile to compen~ate only for axial Yiewing positions.
In accordance with this invention the lenticule profile (i.e., the cross-sectional shape which determines its refractiv~'characteristics) varies as a function of distance from the origin 0,0 in such manner that the reflection loss gradient is at least partly~compensated. The profile varia-tion QCCurs in all four rectangular coordinate directions leading away from'~he origin 0,0: i.e., up,~down, left and right; or +y, -y, -x and ~x. The purpose of the profile variation isto insure that, at any given viewing position wlthin a selected angular viewing range, an observèr will see an imageframe on the screen 10 which appears more nearly uni-formly-bright from side to side and also from top to bottom.
Moreover, the angularviewing range withi~ which this desirable result is o~tained should not be limited to a linear locus (suchas the screen axis 17~ as the prior art did;-but .
~ should constitute a solid angle extending above, below and ~ on both sides of the axls, so that a large fraction of the space in front o~ screen 10 is available for viewing on a ,. . .
c~m~ensated basis~ ' The design objective of the invention is to insure that, for any given position within the angular viewing range, the ~raction of the incident'image light which is refracted to that position becomes larger as the absolute value of the lenticule screen location coordinate increases, i.e., as the positive or negative value of x or y increases, for lenticule arra~s 18 and20. The pro~ile variation of lenticule ar-ray 1~ sompensh~es at least partly for the horizoncal reElection Docket 999 ~ ~ ~72~8 gradient, so that observers A, B and C all see an image frame which app~ars more nearly uniformly bright rom side to aide;
while the profile variation of lenticule array 20 compensates for ~he vertical reflection gradient, so that obse~vers D, E and F all see an image frame which appears more nearly uniformly bright from top to bottom.
By way of example, lenticule 18.1 loses by rearward reflection more of the.image light incident thereon .. :. . . .
than does len~icule 18.2. The foxmer is more remote from axis 17 than is the latter; therefore the angle of incidence ~ of the incident liyht (measured relative to screen normal :~ 28) is larger for lenticule 18.1 than it is or lenticule 18.2; and the physical laws of xeflection require that the - fraction of the incident radiation which is reflected from the air-screen interfaces increases, and the frac~ion ~: which crosses those interfaces decreases, for increasing : ~ value of ~ The same i5 txue for the other array 20;
; for example, when lenticule 20.1 is compared with lenticule ~ ; ~0 2.
Consequently, if lenticules 18.1 and 18.2 were :shaped so that they both refracted toward an~ given observer ;positlon A, B or C, the same fraction of the image l~ght il which succeeds in cxossing the reflecting interfaces, , then a stronger signal would come to that position from ~ lenticu1e 18.2 than from lenticule 18.1, because the formex has : ~ more interface-crossing light available to it. The portion ::: ' : .
of the image which an ob~exver at any position A through C
: receives from lenticule 18.1 would then appear dimmer than :~ the por-tion received by that observer fxom lenticule 18.2.
Thus, a portion of the image within a vertical band at the _ ~ 6 -..~;,. . .
Docket 999 .. . .
0dge of the screen 10 correspondi.ngto lenticule 18.1 would be dimmer than the adjacent v~rtical bandcorresponding to lenticule 18.2. For the same reasons, a similar brightness di~erential would appear between any other pair of vertical lenticules in array 18 which:havedifferent absolute values of the x screen coordinate, and any pair of hoxizontal lenticules in array 20 which have different absolute y coordinate values.
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The inven~ion, however, introduces a difference in refractive pro~ile between each such pai~ o~ lenticules, and cal~ulates these'different profiles so that a greater fraction of thQavailable image light is directed to any -:
given o~server position such as A, ~ or C by the more remote (higher absolute x coordinate value3 lenticules in array 18 '':
than is directed to that same position by the less remote (lower absolute x coordinate value) lenticules in that array.
: ~ Similarly, a greater fraction of the a.vailable image light i8 directed to any given observer position such as D, E, :~ . or ~ by the more remote (higher absolute y coordinate value) ~20 lenticules in array 20 than is directed to that same position ;by the less remote (lower absolute y coordinate value) lenticules in that array.
Obviously, itis a phys.ical impossibility for .. the more remote lenticules to increase the fraction of the ' aval].able light which they direct toe_~y observer position simultaneously~ because any particular lenticule only has , . ~ .
a finite amount of interface-crossing image light available to it or rèfraction, and it ~ust function within those : supply limits. Therefore, the invent.ion ~elects a particular ~30 vertical angle anda particular'horizontal angle as the Docket 99g .
~ 1 ~7~98 viewing ranges within which the arrays 18 and ~0 will be com-pensated for reflection loss differentials, and accepts the fact that observers taking viewing positions outside those ranges will not see a controlled brightness distribution across the ima~e frameA Once these design limits have been chosen, lenticule array 18 is designed so that each lenticule steals some light from those viewing angles which are outside the horizontal target range, and redistributes the stolen light as necessary to increase the amount which is refracted to viewing positions such as A, ~
and C which are within the horizontal target~ rangeA In similar fashion, lenticule array 20 is designed to steal light from view-ing angles which are outside the vertical target range, and use it to increase the amount refracted to observer locations D, E
and F within the range.
The lenticules which are more remote from ~he axis 17 : must steal the most light, and therefore have the narrowest com ~ ; . pensa~ed viewing angle. Thus, the maximum vertical and horizontal ~ : viewing angles for which full reflection compensation is achiev~d by the most extreme lent1cules (e.g~, 18.1 and 20.1) in each ~20 array must be at least equal to the minimum vertical and hori-zontal viewing angles which are selected as design targets for ths~screen as a whole.
ll The particular sequence of lenticule profiles for each I . .:
; array 18 and 20 which will achieve such reflection compensation depends upon a number of design conditions, such as the desired ~:compensation pro~ile (i.e., how close to uniform brightness one can get for ~he worst viewing positions within the compensated : viewing range), the vertical and horizontal screen dimensions, the spacing of the lenticule5 within each array, the index of refrac- .:
30 . tion of ~he screen material, the distance from projectox to , Docket 999 i ~ 3 ~72~
~creen, the minimum ~xp~cted angular spacing between viewers, the shape of the average or overall screen brightness fall-off profile a5 a function of observer azimuth relative to the screen, the curvature (if any) of the screen, the average screen-to-viewer dista~ce, the desired half-brightness fall-off azimuth angles, and of course, the limits of the ranges of vertical and horizontal viewing angles within which reflection loss compensa-tion is to be accomplished~
Thus, the particular sets of lenticule profiles which are quantitatively illustrated in Figs~ 4 and 5 are applicable only .. . . ..
to a particular preferred set of design conditions, such as a screen material having an index of refraction of 1.4913, a hori-zontal half-brightness fall-off azimuth angle of 22.5 on each side~of the axis, a vertical half-brightness fall-off angle of ~ above and below the axis, horizontal and vertical reflection compensation angular ranges which are selected to be equal to the ; ;; :horizontal and vertical half-brightness fall-off angles respec-tively, and triangular fall-off profiles for both the brightness : ~ v~ariation across the scrëen and the average or overall screen 20~ : brightness as a function of observer azimuth. While the best way to disclose:an invention of this nature is to illustrate such a preferred:embodimeDt to scale, as has been done in Figs. 4 and 5, ; it:will be appreciated that the invention is broadly applicable to all sets of design conditions-, and that the design principles exemplified by l;'.i~s. ~ and S may be generalized to any other condikions.
: ~ The sets of lenticule profiles in Figs. 4 and S are not complete; because ~or brevity they show only a portion of only one l1alf (:Lcft or ricJht, top or hottom) oE a screen; and because _ f C~_ ' 2 ~ ~
for clal ity they include oaly samp'Le pro:Eiles selected at regular in-t.ervals, omi-t~inq -the in~ermedi.ate lenticules between sample points. But those proEiles which are shown are suEficiently representative to indicate enti.re vertical and hori~.ontal halE-screell sequences by providing a basis for interpolat.ion of the in-termediate lenticule profiles;
and the opposi-t.e half-screen sequences are mirror images t'hereof~ Thus, it is only necessary that the profiles which are illus-trated indicate the nature of the changes i0 in lenticule profile, and the rates of those changes, from each sample point to the next.
The calculations required to generate the lenticule prof~les for a screen of any practical size are both complicated and 1:ime-consuming. Therefore, the best mode of perEorming such calculations is by means of a suitably p.rogrammed general purpose digital computer. A print-out ; of the computer program listing used to generate the sets of lenticule profiles exemplified hy Figs. 4 and 5 is found in applicant's corresponding UOS. Patent No. ~,387,959, 2~) issued June 14, ].983. These profile sets incorporate changes in lenticule profile as a function of screen coordinate wllich are designed to partially compensate for the refl.ection loss gradient in accordance with this invention; and in accordance with a preferred embodiment 'they are also designed to compensate for the cosine power fall-off as a function of screen coordinate, and to perform the collimating function as well in order to eliminate the :: :
; need for a separate Fresnel or other type of field lens.
The first of these programs, entitled PROJ4B, is used to calculate the lenticule profiles on the projector side of the screen; and the second, en-titled PROJ3~TAB, is used to calculate the lenticule profiles on the viewer .ng~ - 20 -- .
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slde of the screen. PROJ~ is summarized in flow chart form in Fig. 6, and PF~OJ3ATAB in Fig. 7.
As indica-ted i.n ~ig. 6, the pro~ector-side 1.enticule profiles are calculated by first reading a set of input paxameters (flow chart step 100). These parameters include a first lenticule screen loca-tion, the screen-to-viewer distance, the lens-to-screen distance, the screen index of refraction, the desired shape of the brightness distribution (e.g. linear)~ the desired half-brightness angle, the desired lenticule period (i.e. the lenticule spacing), the X-axis increments at which one wishes to calculate the slope angles of successive lenticule profile elements (i.e. the resolution of the profile calculation), and an initial slope angle.
Then from these parameters a set of initial conditions is calculated (flow chart step 102), and a point on the lenticule profile is chosen (flow chart step 104) at which to calculate the slope and length of an initial : ::
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lenticule profile element. For this point and these conditions a s-tarting ray angle to the viewer is calculated (~low chart step 106), and the brightness of the ray is calculated by means of a subroutine (flow chart step 108).
At first, the a~gle calculated will not be more than the maximum allowed (flow chart step 110), and so the pro~
gram tests to see if the brightness is too low (flow chart step 114). If it is too low, then the ray angle in flow chart step 106 is incremented (arrow 113) and the program resumes from flow chart step 106. If not, then the trans-mission loss is calculated (flow chart step 114), using a transmission calculation subroutine (flow chart step 116).
If the resulting light transmission is too low (flow chart step 118), the ray angle in flow chart step lOZ is incremented (arrow 119), and the program resumes from flow chart step 1060 If not, the program calculates the slope angle and length of a lenticule element necessary to give the desired brightness and ray angle tflow chart step 120) A
2D Then a transmission calculation subroutine ~flow chart step 122) is employed to calculate the light trans-mission once again. If the transmission is too low ~flow chart step 124), the ray angle in flow chart step 106 is ; I.ncremented (arrow 125) and the program resumes from flow chart step 106~ If not~ then the coordinates of the endpoint of the lenticule pro~ile element are calculated (flow chart step 126) and the program increments (arrow 127) the point on the lenticule profi:Le in flow chart step 104 and resumes ~ from that stepO
After man~ calculation loops, ~he angle calculated in 10w chart step 106 is more than the maximum allowed (see flow chart step 110), which means that the program has ........... .completed its appointed tasksl and it escapes from the loop .~. ~,~
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arrow 128). After performing a few final calculations (flow chart step 130: normalizing the coordinates of the lenticule profile elements to fit the desired lenticule pitch, adjusting signs, and equalizing the X-a~is steps) and writing the lenticule coordinates to the output file (flow chart step 132), it ends.
These steps are then repeated for each different lenticule profile at each different location on the projector side of the screen.
A5 indicated in Fig. 7, the viewer-side lenticule profiles are calculated by first reading a set of input parameters (flow chart step 150). These parameters include a first lenticule screen location, the screen-to-projector distance, the lens--to-screen distance, the screen index of refraction, the desired shape of the brightness distribution (e.g. linear), the desired half-brightness angle, the desired lenticule period (i.e. the lenticule spacing), and the X-axis increments at which one wishes to calculate the slope angles ; of successi~e lenticule profile elements (i.e. the resolution ~20 of the profile calculation).
Then from these parameters a set of initial condi-;tions is calculated (flow chart step 152), and an initial point on the lenticule pxofile is chosen (flo~ chart step :
154) at which to calculate the slope and length of an initial lenticule profile element. For this point and these condi-tions a starting lenticule profile elements slope is chosen (flow chart step 1563.
A~t flrst, the slope chosen will not be more than the maximum allowed ~flow chart step 158), and so khe program ~tests to see if total internal reflection results (flow chart step 160j. If so, then the slope an~le in flow chart step-156 is incremented (arrow 161) and the program resumes ^ from flow chart step 156. If not, then the refraction angle j r/l~/ .
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is calculated (flow chart step 162) and a light transmission calculation is perEormed, using a transmi.ssion calculation subroutine (flow chart step 164).
If the resulting light transmission is below a selected minimum (flow chart step 166, the slope angle in flow chart step 156 is incremented (arrow 167), and the program resumes from flow chart step 156. If not~ the desired brightness at the viewing angle under consideration is calculated by means of a brightness calculation sub-routine ~flow chart step 168), and the lenticule element length necessary to produce the desired brightness is then calculated (flow chart step 170).
If the brightness is below a selected minimum (flow chart step 172), the slope angle in flow chart step 156 is incremented (arrow 173) and the program resumes from flow chart step 1560 If not, then the coordinates of the endpoint of the lenticule profile element are calculated (flow chart step 174) and the program increments the point on the lenticule profile in flow chart step 154 and resumes from~that point.
: ~ After many calculation loops, the incremented.
angle in flow chart step 156 exceeds the maximum allowed ~: (see flow chart step 158), which means that the program has :~; completed its appointed tasks, and it escapes from the loop arrow 176). After performing a few final calculations (flov chart step 178: calculatlng the last coordinate of ~the lenticuIe and adjusting the coordinates to equalize the X-axis steps) and writing the ~enticule coordinates to the output file (flow chart:step 180), it endsO
~30~ These steps are then repeated for each different lenticule profile at each different location on the viewer :: .
:; side of the screen.
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The result is an economical. single-sheet type of rear project:ion screen which cornhines therein -lhe co:Llimating and the horizontal and vertical light distributing functi.ons, and which is advantageously compensated for cosine power fall-o:Ef oE the incident i.mage liyht intensity. This ~creen i9 also, for t:he first time, compensated for the reflection loss gradient over a range of off-axis viewing positions, over both vertical and horizontal angular viewing ranges~ And also for the .Eirst time, compensat:ion for the reflection loss gradient is achieved by means of a sequence of lenticule profile changes as a function of one or more screen coordinates.
: The described embodiments represent the preferred form of the invention, but alternative embodiments may be lmagined which would come within the novel teachings herein.
Accordingly, these embodiments are to be considerecl : as merely illustrative, and not as limiting the scope of the following claims.
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t Docket 999 1 16~9~3 Single sheet screens are leqs expensive and le~s rPflective, but the design constraints are more severe because they have only two surfaces on which k place lenticular arrays.
Some oE the single sheet designs have a Fresnel ield lens on one side for collimation, and a vertical rectilinear lenticular array on the other side for horizontal distri-bution. Sincethat takes up all the available surfacPs, ~creens of thiq type often rely upon a light~diffusing ti.e. translucent rather than transparent) layer to sprPad the image light vertically.
. The use of diffusion for this purpose, however, has its disadvantages. ~iffusion hy i~s nature cannot be confined to the vertical direction, and so it affects the distribution of light in the horiæontal direction as well.
Diffusion is also a less efficient method of image,light distribut.ion than re~raction, owing to the significant amount of backward reflection, and also some absorption, attributable to the diffusion layer. In addition'ambient light is reflected hack to the viewer degrading contrast. ~Xe amount of d.iEfusion which occurs is. also diffieult to eontrol.
If the diffusion element is applied as a surface co~ting, uniform thickness is difficult to achieve. Such ::~ coatings also tend to fill in the valleys between the ridges of a lenticular array. If diffusion is achieved by molding the screen with a rough surface texture, then the mold must be carefully maintained ~o preserve its surface characteristics over a large number of pressings.
Furthermore, some of the resin may adhere to the rough surface of the mold, which reduces the ability of the ~creen to diffuse light, and also makes its removal from the ~ld mor~ difficult. Another appro;ch to diffusion is the use -'' of light-dispersing pigment granules or other optically active particles mixed with the screen resin before pressing.
It is important, when using this approach, to make sure that the diffusion material is dis-tributed uniformly across the screen, or non-uniform brightness distributions may occur, causing poor image quality. On the other hand, if the diffusion material is distributed throughout the thickness of the screen, as is usually the case, the focal -plane of the projected image is not distinct, which results in loss of image sharpness. Another problem is that the presence of the diffusion material may affect the molding and handling characteristics of the resin.
The present invention relates to a projection screen for use with projection means located rearwardly of the screen for displaying an image to a plurality of observers located at viewing positions which are on the front side of the screen and dispersed in a direction parallel to the screen; the projection means defining an axis; the screen including at least one array of substantially rectilinear lenticuies having respective light-refracting cross-sectional shapes adapted to redirect light arriving from the rear side of the screen so that an image formed on the screen by the light is visible at the dispersed positionsj the .
respective cross-sectional shapes of the lenticules varying as a function of their distance from the axis in such manner that, for each position within a selected angular viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from the axis than is directed to that viewing position from those lenticules which are closer to the axis, so as to at least partially compensate for the lmage light rearward reflection loss gradient; the lenticule cross-sectional shapes being defined by a succession of mg~o ~ ~ ~
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lenti.cule profile elements; the slope angle, lengtll and position of each of the len-ticu]e profile elements ~eing determined by an algori-thm which calculates the light transmission provided by each of the lenticule profile elements, and adjusts the slope angles, lengths and positions thereof to achieve the reflection loss gradient compensation.
In its method aspect, the invention relates to a method of manufacturing a projection screen for use with projection means located rearwardly of the screen for disp].aying an image to a plurality of observers located at viewing positions which are on the front side of the screen and dispersed in a direction parallel to the screen;
the projection means defining an axis; the screen including at least one array of substantially rectilinear lenticules having respective light~refracting cross-sectional shapes adapted to redirect light arriving from the rear side of the screen so that an image formed on -the screen by the light is visible at the dispersed positions;the respective cross-sectional shapes of the lenticules varying as a function of their distance from the axis in such manner thatj for each position withi.n a selected angular viewing range, a greater Eraction of the ,incident image light is directed to that viewlng position from those lenticules which are further from the axis than is directed to that ~: :
~ :viewing position from those lenticules which are closer : :
to the axis, so as to at least partially compensate for the image light rearward reflection loss gradient; the lenticule cross-sectional shapes being defined by a 30~ succ~ession of lenticule profile elements; the method comprising the steps of: calcuLati,ng the light transmission provided by each of the lenticule profile elements; and adjusting the slope angle, length and position of each ,~`
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of the lenticu]e profile elements in a manner to alterthe light -transmission to achieve the reflection loss gradient compensation.
Thus, the present invention contemplates a single-sheet ~or two-surface) screen design which does not employ diffusion for vertical distribution. It employs a fully transparent, non-diffusive material which is formed into a sheet having a vertically running, horizontally dispersing rectilinear lenticular array on one surface, and a horizontally running, vertically dispersing rectilinear lenticular array on the other surface. Since there is no other surface left on which to form a field lens, the collimating function is built into the refractive characteristics of the two lenticular lenses. Since the angle of incidence of the image light varies from 0~ at the axis of the projection system to progressively larger angles with increasing distance from the axis, the collimating function requires the refractive properties of the lenticules to vary as a function of screen position.
20 ~ Hence their cross-sectional shape changes from lenticule to lenticule across the surface of the screen.
Change of lenticule shape as a function of .
screen coordinate was employed by the prior art for thls purpase~in a number of spiral or circular Fresnel field lens ~ : :
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mg/~o - 4b -:, , Docket 999 designs and also in some rectilinear lenticular arrays. Some prior art rectilinear lenticular arrays also change the lenticule cross-sectional shape as a function of screen coordinate for another purpose, i.e., in order to compensate for the cosine power fall-off in image light intensity as a function of angle of ray divergence, which results from the inherent characteristics of the projector focussing lenses.
It appears, however, that no prior art screen varies the lenticule cross~sectional shape as a function of screen coordinate in a manner to compensate even partially for the fact that the reflection losses are greaker at greater distances from . . .
the projection axis. It is especially important to do this in a ~creen of the present type, because thé use of two orthogonal distributive lenticular arrays would otherwise produce unacceptable brightness gradients in both the vertical and hori-zontal directions due to the reflection differential across the height and width of ~he screen.
The problem of reflection loss gradient has been recog~
nized in Strong et al., U. S. Patent No. 2,200,646. That ~0 reférence, however, is not concerned with one or more angular ranges of viewing positions. It is only concerned with a linear range of viewing positions extending along the axis~ with only tha perpendicular distance from the screen as a variable para-meter. In Strong the projected image is used only as a cinema backdrop, and thus there is only one "observer", i.e., a movie camera which is always set up in some axial position, rather than a plurality of ~npredictable human observers who may take viewing positions above, below, or to either side of the axis. Therefore, -5~
~ Docket 999 I 1 ~72~
the brightne~s gradient i5 eliminated only for axial viewing positions at various perpendicular distances ~rom the screen. No compensa~ion i5 provided or a range o~ off-axis viewing positions dispersed in any direction parallel to the screen, such as horizontally and vertically.
If that screen design were used in a projection TV system, all viewers would have to take up single-file positions directly on the axis, otherwise the brigh~ness of the pro-jected image-would vary vertically or horizontally or both.
Moreove~, the Strong patent uses the same lenti-cule cross-sectional shap`e at each location. The limited degree of compensation for differential reflection which ; ~ is described in ~h~ patent results solely from th~ fact that the light reaching a given axial viewing position, from any two lenticules having different screen coordinates, læ refracted ~rom different facets of the lenticule pro-fileO Thus, no use is made of the concept of lenticule ' shape change for the purpose of compensating reflection `-' differentials. ~ , In the present invention, the lenticules vary as a \ - -function o screen coordinate in such manner that reflection ;-differentials are at least partly compensated for each one of a selected range of viewing positions extending in at least one direction parallel to the screen, ~ , vertically and/or ~orizontally. The variation is such that, for each viewing position within the selected hori ontal and/or vertical viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from the axis than is dlrected to that viewing position from -those lenticules which are closer to the axis.
Docket 999 9 ~
This compensates at least partially for the gxeatex image light loss due to rearward reflection ~uffered by those lenticules which are further from the axis, as compared to those lenticules which are closer to the axis.
In the preferred form of the invention, both the vertical and horizontal lenticular arrays are so compen-sated. Thus, at any viewer position within a selected horizontal viewing angle and a selected vertical viewing anyle, the observer willsee a projected image field which is uniform in brightness from top to bottom and from left to right.
The foregoing background discussion;and brief description of the invention, as well as its features and advantages, will be more fully understood by reference to the following detailed description of the preferred .
embodiment of the invention, when read in conjunction with the following drawings.
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- Brief Description ~2~0 of the Drawin~s Fig. 1 lS a top plan view, schematic in nature, j~ ; of a rear projectlon system employing a lenticular screen n accordance with this invention.
Fig. 2 is a side elevational view, schematic in na~ure, of the same projection system.
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Fi.g. 3 is a perspective view of a f~agmen-t of a single-slleet rear projection screen which is employed in the projection system of Figs. 1 and 2, and which has respective lenticular arrays on opposite faces thereof.
Fig. 4. is in the nature of a horizontal cross-section, and shows the light refracting cross~sectlonal profiles of an incomplete but representative number of lenticules se].ected from a vertically extending, horizontally distributing array formed on the front 1.~ (viewer) side of the rear projection screen of Figs.
1 through 3~
Fig. 5 is in the nature of a vertical cross-section, and shows the light-refracti.ng cross-sectional profiles of an incomplete but representat.ive number of lenticules selected from a horizontally extending, vertically distributing array formed Oll the rear (projector) side of the rear projection screen of Figs. 1 through 3.
Fig. 6 is a flow ehart summarizing a computer program for calculating the profiles of the lenticules on the proieetor slde of the lenticular sereen of this inventionO
Fig. 7 is a flow ehart summarizing a computer ;: program for ealculating the profiles of the lentieules :
- ~ ~ on the ~iewer side of the lentieular sereen of this invention.
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F:L9S. 1, 2 and 3 are intended to represellt the invention in a qualitative fashion only, as patent drawings usually do, and therefore are not dra~n -to scale.
Figs. 4 and 5, on the other han.d, which are profile diagrams of screen lenticules used in Figs through 3, are drawn substantially to scale in order to represent quantitatively, and wi-th precision, a typical sequence of lenticule cross-sectional shapes i.n accordance with this invention. Scales are provided in inches along the axes of these drawings, and the specific dimensions indicated are for a particular embodiment of the invention which is preferred. The illustrated proiles exemplify the nature of the changes in the cross-sectional shapes of the lenticules across -the screen, and also the rates of such changes, for a particular set of screen dimensions ana a particular set of enyineering objectives and design parametars;
but the scope of protecti.on to be afforded thi.s invention ;~20 of course extends to any set of design conditlons.
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Detailed Description of the Preferred Embodiment ~ ~ O -As seen in Figs. 1 through 3, an upright rear projection screen 10 in accordance with this inventiQn preEerably comprise~
a single sheet 11 formed of plastic material by any conventional process, such a compression-molding, casting~ or roller extrusion.
The invention, however, could just as well be used with two or more such sheets bonded together face-to-face in order to form a unitary str.ucture having only one foxward facing surface and one rearward acing surface, because in that case the bonded sheet would in effect have only two air inter~aces at which undesirable forward ox rearward reflec~ions can take ~lace.
The invention could be applied to multiple sheet screen designs .
also~ but that would not be preferable because then there would be four or more air interfaces at which reflection losses could occur. ~ ~
Any of the conventional light-transmitting polymers which are ordinarlly used in the art to Porm rear projection screens will be satisfactory for this purpose; but, since diffusion is not relied on for light distribution in this invention, best results will be obtained~with a fully ~xansparent material having 20~ no~plgment granu~es or other optically active substances incor-porated~therein. It also~follows that the suxface of the sheet 10 sho~Id be smooth (untextured~ on a ~ublenticular scale, and no~dif~usion coatin~ should be employed. But the invention, if :
desired~ may be employed with an opaque dark coating (not shown) ; distribu~ed, in a pattern known to~the art, so as to form a black surround to reduce the reflection o~ am~ient light incident UpQn the front (viewer) surface of the screen, and thus improve the contrast (or optical signal-to-noise ratio).
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--10-- , ,: , ' , , Docket 999 I ~ ~7298 A projector 16 on the rear side of the screen 10 has a generally horizontal optical axis17, which inter-~ects the screen at an axial point designated 0,0 because lt forms the origin of a system of x, y rectangular coor-dinates useful or designating lenticule positions on either side of the screen lQ. Normally, but not necessarily, the projection system would be arranged so that the origin is at the geometric center of the screen. The rectangular coordinates of which we will speak are oriented horizontally (x) and vertically (y) respectivel~, and both of them .~
numerically increase in ~ositive and ne-~ative directions from the origin as is conventional.
The sheet 11 has only two ~urfaces avail~ble on which to form lenticular arrays: a front surface 12 facing viewers A through F, and a rear surface 14 facing projector 16. A-vertically~running array 18 of parallel rectilineax lenticules 18.1, 18.2, etc. is formed on the front screen surface 12 for the purpose of horizontally distrihuting the~image light supplied by projector 16 20~ ` to viewers A, B, a~ndC who are at locations dispersed horizontally over a range~extending~to both sides of axis~17; i.e., these viewers are seated at different azimuth p~ositions relative to screen 10. A horizontally running array 20 of parallel rectilinear lenticules 20.1, 20.2, .
etc.-is formed on~the rear surface 14 for the purpose of vertically distributing the image light supplied by projec~or 16~to viewers D, E, and F who are a~ locations dispersed vertically over a~range extending both above and below axis 17; ~ , these viewers are people of different sizes : ' .
~ sitting in chairs of different heights located at different -Docket 999 ~
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distances from the screen. The lenticules may be conveniently formed by compression molding, as is conventional in the art.
The use of such lenticular arrays for vertical and/or horizontal distribution of image light is old, as i5 the concept of a scxeen comprising a single sheet.
The range of horizontal light distribution exceeds the range o~ vertical distribution,because there is not as mu~h angular difference vertically between the heads of .
seated viewers as there is horizontally between chair locations.
It is an inherent ~roperty of pro~ection screens that the - overall brightness o-f a projected image has a profile which un-avoidably decreases with increasing angle of view, relative to the screen axis, in the vertical and horizontal directions.
Conventionally, the useful angular range is arbitrarily-defined as that which is bounded by the half-brightness fall-off angles.
In a typical design the vertical half-brightness fall-off need only be of the order of 8 above and below the axis, whereas the horizontal half-brightness fa~l-off should be of the order of 22.5 leEt and right of the axis in order to optimize viewer ~20 ~ocatLons and screen brightnes6.
Since the angular range of vertical distribution is the smaller of the two, the horizontally running, vertically di~-tributing array 20 has less re-entrant groove area. Preferably, ~ ~ ~ then, lenti~cule array 20 is chosen to ~e located on the rear sur-;~ face 14 so as to minimize the rearward reflection of image light from re-entrant areas. The black surround coating, if used, is located on the ront surface, which permit~ the use of a thlcker and therefore stronger screen, and allows a grea~er thickness ; tolerance and a grea1ter tolerance for inaccuracies in the deposi-tion pattern of the black coating. This is because the coating _ / c;? _ Docket 999 . :
ha~ gaps which mus~ be located at the foci of the opposite lenticules 20, and these foci are smaller and/or can be located further from the lenticules 2p when the latter have a smaller angular light spread.
It is old in this art to vary the light-refracting ¢ross-sectional shapes of lenticules 18,1, 18.2, etc. and/or 20 1, 20.2, etc. for certain purposes as a function of the ~istance of the lenticules from origin 0;,0. Thus, image rays such as 22 which s~rike at or near the horizontal extreme~ of the screen 10 have a larger angle of incidence ~ measured .. . . ... ~ . . - ~ . - , -relative to a screen-normal line 28, than those rays which strike at or near the axis 17. The same may be said or rays 24 which strike at or near the vertical extremes. The ~rior art, accordingly, varied-the light-refracting cross~sectional shapes of these lenticules as a ~unction of horizontal and vertical ~creen~coordinates so as to refract the image rays more at screen locations more distant ~rom the origin, and less at screen .
locations less ~istant from the origin. This serves to collimate the lmage rays without the need for a separate field lens ~20 ~ such a circular or spiral Fresnel, an important consideration in a single-sheet screen deslgn which has no room ~; for a separate field lens. The present invention, in oommon with the prior art, varies the lenticule pro~iles in arrays 18 and 20 in this manner and for this purpose.
' ~ ~ ' .
_ ~3_ ~ :
.
Docket 999 ~ 1 ~7298 Additionally, any off-axis ray (such as 22 and 24) suffers a loss in intensity which is ~ function of a power of the cosine of the diveryence angle 0 between that ray and the axis 17, a fact which results rom the inherent characteristics of the focussing lens assembly 26 of pro- ~
jector 16. The prior art has compensated for this efect hy varying the shape of the lenticules as a function of vertical and/or horizontal s~reen coordinate so that more image li~ht is refractedto any given viewer position by those lenticules 18 or 20 which are further away from the axis 17 than is rerac-ted thereto by those lenticules 18 or .
20 which are closer to the axis. In common with the prior art, this invention also varies the lenticule shapes in both arrays or -this purpose.
As recognized in the Strong patent, there is yet another pararneter which varies as a unction of screen coordinate. The rays (such as 22 and 24) which are further from the axis 17 have a higher angle of in~idence ~ than those nearer the axis, and as a result the fraction of the imag~ light which is lost because of backward reflection from the air interEaces (front and back surfaces 12 and 14 of the sheet 11~ is gre~tex as distance from the axis 17 increases.
If this is uncorre~ted, an observer at any viewing position will notice that the projected image is brighter at the center of screen 10 (origin 0,0) ~han it is at any location above, below or on either side thereo. Even if the compensation scheme of Strong et al. is employed, the same problem is encountered for all viewing positions which are off-axis.
Strong, as noted, does not suggest changing the lenticule --1'1-- ~
, Docket 999 7~9~
profile as a function of screen coordinate, and uses a con-stant lenticule profile to compen~ate only for axial Yiewing positions.
In accordance with this invention the lenticule profile (i.e., the cross-sectional shape which determines its refractiv~'characteristics) varies as a function of distance from the origin 0,0 in such manner that the reflection loss gradient is at least partly~compensated. The profile varia-tion QCCurs in all four rectangular coordinate directions leading away from'~he origin 0,0: i.e., up,~down, left and right; or +y, -y, -x and ~x. The purpose of the profile variation isto insure that, at any given viewing position wlthin a selected angular viewing range, an observèr will see an imageframe on the screen 10 which appears more nearly uni-formly-bright from side to side and also from top to bottom.
Moreover, the angularviewing range withi~ which this desirable result is o~tained should not be limited to a linear locus (suchas the screen axis 17~ as the prior art did;-but .
~ should constitute a solid angle extending above, below and ~ on both sides of the axls, so that a large fraction of the space in front o~ screen 10 is available for viewing on a ,. . .
c~m~ensated basis~ ' The design objective of the invention is to insure that, for any given position within the angular viewing range, the ~raction of the incident'image light which is refracted to that position becomes larger as the absolute value of the lenticule screen location coordinate increases, i.e., as the positive or negative value of x or y increases, for lenticule arra~s 18 and20. The pro~ile variation of lenticule ar-ray 1~ sompensh~es at least partly for the horizoncal reElection Docket 999 ~ ~ ~72~8 gradient, so that observers A, B and C all see an image frame which app~ars more nearly uniformly bright rom side to aide;
while the profile variation of lenticule array 20 compensates for ~he vertical reflection gradient, so that obse~vers D, E and F all see an image frame which appears more nearly uniformly bright from top to bottom.
By way of example, lenticule 18.1 loses by rearward reflection more of the.image light incident thereon .. :. . . .
than does len~icule 18.2. The foxmer is more remote from axis 17 than is the latter; therefore the angle of incidence ~ of the incident liyht (measured relative to screen normal :~ 28) is larger for lenticule 18.1 than it is or lenticule 18.2; and the physical laws of xeflection require that the - fraction of the incident radiation which is reflected from the air-screen interfaces increases, and the frac~ion ~: which crosses those interfaces decreases, for increasing : ~ value of ~ The same i5 txue for the other array 20;
; for example, when lenticule 20.1 is compared with lenticule ~ ; ~0 2.
Consequently, if lenticules 18.1 and 18.2 were :shaped so that they both refracted toward an~ given observer ;positlon A, B or C, the same fraction of the image l~ght il which succeeds in cxossing the reflecting interfaces, , then a stronger signal would come to that position from ~ lenticu1e 18.2 than from lenticule 18.1, because the formex has : ~ more interface-crossing light available to it. The portion ::: ' : .
of the image which an ob~exver at any position A through C
: receives from lenticule 18.1 would then appear dimmer than :~ the por-tion received by that observer fxom lenticule 18.2.
Thus, a portion of the image within a vertical band at the _ ~ 6 -..~;,. . .
Docket 999 .. . .
0dge of the screen 10 correspondi.ngto lenticule 18.1 would be dimmer than the adjacent v~rtical bandcorresponding to lenticule 18.2. For the same reasons, a similar brightness di~erential would appear between any other pair of vertical lenticules in array 18 which:havedifferent absolute values of the x screen coordinate, and any pair of hoxizontal lenticules in array 20 which have different absolute y coordinate values.
.. .. . . . . . .
The inven~ion, however, introduces a difference in refractive pro~ile between each such pai~ o~ lenticules, and cal~ulates these'different profiles so that a greater fraction of thQavailable image light is directed to any -:
given o~server position such as A, ~ or C by the more remote (higher absolute x coordinate value3 lenticules in array 18 '':
than is directed to that same position by the less remote (lower absolute x coordinate value) lenticules in that array.
: ~ Similarly, a greater fraction of the a.vailable image light i8 directed to any given observer position such as D, E, :~ . or ~ by the more remote (higher absolute y coordinate value) ~20 lenticules in array 20 than is directed to that same position ;by the less remote (lower absolute y coordinate value) lenticules in that array.
Obviously, itis a phys.ical impossibility for .. the more remote lenticules to increase the fraction of the ' aval].able light which they direct toe_~y observer position simultaneously~ because any particular lenticule only has , . ~ .
a finite amount of interface-crossing image light available to it or rèfraction, and it ~ust function within those : supply limits. Therefore, the invent.ion ~elects a particular ~30 vertical angle anda particular'horizontal angle as the Docket 99g .
~ 1 ~7~98 viewing ranges within which the arrays 18 and ~0 will be com-pensated for reflection loss differentials, and accepts the fact that observers taking viewing positions outside those ranges will not see a controlled brightness distribution across the ima~e frameA Once these design limits have been chosen, lenticule array 18 is designed so that each lenticule steals some light from those viewing angles which are outside the horizontal target range, and redistributes the stolen light as necessary to increase the amount which is refracted to viewing positions such as A, ~
and C which are within the horizontal target~ rangeA In similar fashion, lenticule array 20 is designed to steal light from view-ing angles which are outside the vertical target range, and use it to increase the amount refracted to observer locations D, E
and F within the range.
The lenticules which are more remote from ~he axis 17 : must steal the most light, and therefore have the narrowest com ~ ; . pensa~ed viewing angle. Thus, the maximum vertical and horizontal ~ : viewing angles for which full reflection compensation is achiev~d by the most extreme lent1cules (e.g~, 18.1 and 20.1) in each ~20 array must be at least equal to the minimum vertical and hori-zontal viewing angles which are selected as design targets for ths~screen as a whole.
ll The particular sequence of lenticule profiles for each I . .:
; array 18 and 20 which will achieve such reflection compensation depends upon a number of design conditions, such as the desired ~:compensation pro~ile (i.e., how close to uniform brightness one can get for ~he worst viewing positions within the compensated : viewing range), the vertical and horizontal screen dimensions, the spacing of the lenticule5 within each array, the index of refrac- .:
30 . tion of ~he screen material, the distance from projectox to , Docket 999 i ~ 3 ~72~
~creen, the minimum ~xp~cted angular spacing between viewers, the shape of the average or overall screen brightness fall-off profile a5 a function of observer azimuth relative to the screen, the curvature (if any) of the screen, the average screen-to-viewer dista~ce, the desired half-brightness fall-off azimuth angles, and of course, the limits of the ranges of vertical and horizontal viewing angles within which reflection loss compensa-tion is to be accomplished~
Thus, the particular sets of lenticule profiles which are quantitatively illustrated in Figs~ 4 and 5 are applicable only .. . . ..
to a particular preferred set of design conditions, such as a screen material having an index of refraction of 1.4913, a hori-zontal half-brightness fall-off azimuth angle of 22.5 on each side~of the axis, a vertical half-brightness fall-off angle of ~ above and below the axis, horizontal and vertical reflection compensation angular ranges which are selected to be equal to the ; ;; :horizontal and vertical half-brightness fall-off angles respec-tively, and triangular fall-off profiles for both the brightness : ~ v~ariation across the scrëen and the average or overall screen 20~ : brightness as a function of observer azimuth. While the best way to disclose:an invention of this nature is to illustrate such a preferred:embodimeDt to scale, as has been done in Figs. 4 and 5, ; it:will be appreciated that the invention is broadly applicable to all sets of design conditions-, and that the design principles exemplified by l;'.i~s. ~ and S may be generalized to any other condikions.
: ~ The sets of lenticule profiles in Figs. 4 and S are not complete; because ~or brevity they show only a portion of only one l1alf (:Lcft or ricJht, top or hottom) oE a screen; and because _ f C~_ ' 2 ~ ~
for clal ity they include oaly samp'Le pro:Eiles selected at regular in-t.ervals, omi-t~inq -the in~ermedi.ate lenticules between sample points. But those proEiles which are shown are suEficiently representative to indicate enti.re vertical and hori~.ontal halE-screell sequences by providing a basis for interpolat.ion of the in-termediate lenticule profiles;
and the opposi-t.e half-screen sequences are mirror images t'hereof~ Thus, it is only necessary that the profiles which are illus-trated indicate the nature of the changes i0 in lenticule profile, and the rates of those changes, from each sample point to the next.
The calculations required to generate the lenticule prof~les for a screen of any practical size are both complicated and 1:ime-consuming. Therefore, the best mode of perEorming such calculations is by means of a suitably p.rogrammed general purpose digital computer. A print-out ; of the computer program listing used to generate the sets of lenticule profiles exemplified hy Figs. 4 and 5 is found in applicant's corresponding UOS. Patent No. ~,387,959, 2~) issued June 14, ].983. These profile sets incorporate changes in lenticule profile as a function of screen coordinate wllich are designed to partially compensate for the refl.ection loss gradient in accordance with this invention; and in accordance with a preferred embodiment 'they are also designed to compensate for the cosine power fall-off as a function of screen coordinate, and to perform the collimating function as well in order to eliminate the :: :
; need for a separate Fresnel or other type of field lens.
The first of these programs, entitled PROJ4B, is used to calculate the lenticule profiles on the projector side of the screen; and the second, en-titled PROJ3~TAB, is used to calculate the lenticule profiles on the viewer .ng~ - 20 -- .
~ ~ 6729~
slde of the screen. PROJ~ is summarized in flow chart form in Fig. 6, and PF~OJ3ATAB in Fig. 7.
As indica-ted i.n ~ig. 6, the pro~ector-side 1.enticule profiles are calculated by first reading a set of input paxameters (flow chart step 100). These parameters include a first lenticule screen loca-tion, the screen-to-viewer distance, the lens-to-screen distance, the screen index of refraction, the desired shape of the brightness distribution (e.g. linear)~ the desired half-brightness angle, the desired lenticule period (i.e. the lenticule spacing), the X-axis increments at which one wishes to calculate the slope angles of successive lenticule profile elements (i.e. the resolution of the profile calculation), and an initial slope angle.
Then from these parameters a set of initial conditions is calculated (flow chart step 102), and a point on the lenticule profile is chosen (flow chart step 104) at which to calculate the slope and length of an initial : ::
: : :
:
:
mg~`~ - 2Oa -~ 1 ~729~
lenticule profile element. For this point and these conditions a s-tarting ray angle to the viewer is calculated (~low chart step 106), and the brightness of the ray is calculated by means of a subroutine (flow chart step 108).
At first, the a~gle calculated will not be more than the maximum allowed (flow chart step 110), and so the pro~
gram tests to see if the brightness is too low (flow chart step 114). If it is too low, then the ray angle in flow chart step 106 is incremented (arrow 113) and the program resumes from flow chart step 106. If not, then the trans-mission loss is calculated (flow chart step 114), using a transmission calculation subroutine (flow chart step 116).
If the resulting light transmission is too low (flow chart step 118), the ray angle in flow chart step lOZ is incremented (arrow 119), and the program resumes from flow chart step 1060 If not, the program calculates the slope angle and length of a lenticule element necessary to give the desired brightness and ray angle tflow chart step 120) A
2D Then a transmission calculation subroutine ~flow chart step 122) is employed to calculate the light trans-mission once again. If the transmission is too low ~flow chart step 124), the ray angle in flow chart step 106 is ; I.ncremented (arrow 125) and the program resumes from flow chart step 106~ If not~ then the coordinates of the endpoint of the lenticule pro~ile element are calculated (flow chart step 126) and the program increments (arrow 127) the point on the lenticule profi:Le in flow chart step 104 and resumes ~ from that stepO
After man~ calculation loops, ~he angle calculated in 10w chart step 106 is more than the maximum allowed (see flow chart step 110), which means that the program has ........... .completed its appointed tasksl and it escapes from the loop .~. ~,~
jr/ ~
, .: ' ' ~ .
~ 3 ~72~
arrow 128). After performing a few final calculations (flow chart step 130: normalizing the coordinates of the lenticule profile elements to fit the desired lenticule pitch, adjusting signs, and equalizing the X-a~is steps) and writing the lenticule coordinates to the output file (flow chart step 132), it ends.
These steps are then repeated for each different lenticule profile at each different location on the projector side of the screen.
A5 indicated in Fig. 7, the viewer-side lenticule profiles are calculated by first reading a set of input parameters (flow chart step 150). These parameters include a first lenticule screen location, the screen-to-projector distance, the lens--to-screen distance, the screen index of refraction, the desired shape of the brightness distribution (e.g. linear), the desired half-brightness angle, the desired lenticule period (i.e. the lenticule spacing), and the X-axis increments at which one wishes to calculate the slope angles ; of successi~e lenticule profile elements (i.e. the resolution ~20 of the profile calculation).
Then from these parameters a set of initial condi-;tions is calculated (flow chart step 152), and an initial point on the lenticule pxofile is chosen (flo~ chart step :
154) at which to calculate the slope and length of an initial lenticule profile element. For this point and these condi-tions a starting lenticule profile elements slope is chosen (flow chart step 1563.
A~t flrst, the slope chosen will not be more than the maximum allowed ~flow chart step 158), and so khe program ~tests to see if total internal reflection results (flow chart step 160j. If so, then the slope an~le in flow chart step-156 is incremented (arrow 161) and the program resumes ^ from flow chart step 156. If not, then the refraction angle j r/l~/ .
, ~ .
~ ~6'~2~3~
is calculated (flow chart step 162) and a light transmission calculation is perEormed, using a transmi.ssion calculation subroutine (flow chart step 164).
If the resulting light transmission is below a selected minimum (flow chart step 166, the slope angle in flow chart step 156 is incremented (arrow 167), and the program resumes from flow chart step 156. If not~ the desired brightness at the viewing angle under consideration is calculated by means of a brightness calculation sub-routine ~flow chart step 168), and the lenticule element length necessary to produce the desired brightness is then calculated (flow chart step 170).
If the brightness is below a selected minimum (flow chart step 172), the slope angle in flow chart step 156 is incremented (arrow 173) and the program resumes from flow chart step 1560 If not, then the coordinates of the endpoint of the lenticule profile element are calculated (flow chart step 174) and the program increments the point on the lenticule profile in flow chart step 154 and resumes from~that point.
: ~ After many calculation loops, the incremented.
angle in flow chart step 156 exceeds the maximum allowed ~: (see flow chart step 158), which means that the program has :~; completed its appointed tasks, and it escapes from the loop arrow 176). After performing a few final calculations (flov chart step 178: calculatlng the last coordinate of ~the lenticuIe and adjusting the coordinates to equalize the X-axis steps) and writing the ~enticule coordinates to the output file (flow chart:step 180), it endsO
~30~ These steps are then repeated for each different lenticule profile at each different location on the viewer :: .
:; side of the screen.
:: ~
.
jr/lll,/ -~ lt 6'~29~
The result is an economical. single-sheet type of rear project:ion screen which cornhines therein -lhe co:Llimating and the horizontal and vertical light distributing functi.ons, and which is advantageously compensated for cosine power fall-o:Ef oE the incident i.mage liyht intensity. This ~creen i9 also, for t:he first time, compensated for the reflection loss gradient over a range of off-axis viewing positions, over both vertical and horizontal angular viewing ranges~ And also for the .Eirst time, compensat:ion for the reflection loss gradient is achieved by means of a sequence of lenticule profile changes as a function of one or more screen coordinates.
: The described embodiments represent the preferred form of the invention, but alternative embodiments may be lmagined which would come within the novel teachings herein.
Accordingly, these embodiments are to be considerecl : as merely illustrative, and not as limiting the scope of the following claims.
:: :
:~ .
,, 1 mg/ ~ - 24 -
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A projection screen for use with projection means located rearwardly of said screen for displaying an image to a plurality of observers located at viewing positions which are on the front side of said screen and dispersed in a direction parallel to said screen;
said projection means defining an axis, said screen including at least one array of substantially rectilinear lenticules having respective light-refracting cross-sectional shapes adapted to redirect light arriving from the rear side of said screen so that an image formed on said screen by said light is visible at said dispersed positions;
said respective cross-sectional shapes of said lenticules varying as a function of their distance from said axis in such manner that, for each said position within a selected angular viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from said axis than is directed to that viewing position from those lenticules which are closer to said axis, so as to at least partially compensate for the image light rearward reflection loss gradient;
said lenticule cross-sectional shapes being defined by a succession of lenticules profile elements;
the slope angle, length and position of each of said lenticule profile elements being determined by an algorithm which calculates the light transmission provided by each of said lenticule profile elements, and adjusts said slope angles, lengths and positions thereof to achieve said reflection loss gradient compensation.
said projection means defining an axis, said screen including at least one array of substantially rectilinear lenticules having respective light-refracting cross-sectional shapes adapted to redirect light arriving from the rear side of said screen so that an image formed on said screen by said light is visible at said dispersed positions;
said respective cross-sectional shapes of said lenticules varying as a function of their distance from said axis in such manner that, for each said position within a selected angular viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from said axis than is directed to that viewing position from those lenticules which are closer to said axis, so as to at least partially compensate for the image light rearward reflection loss gradient;
said lenticule cross-sectional shapes being defined by a succession of lenticules profile elements;
the slope angle, length and position of each of said lenticule profile elements being determined by an algorithm which calculates the light transmission provided by each of said lenticule profile elements, and adjusts said slope angles, lengths and positions thereof to achieve said reflection loss gradient compensation.
2. The screen of Claim 1 which is formed of fully transparent material and comprises a second array of substantially rectilinear lenticules oriented substantially perpendicularly to the first-mentioned array and having respective light-refracting cross-sectional shapes for redirecting said image light in another direction to observers at viewing positions dispersed in a second screen-parallel direction, whereby to obviate the need for diffusion means.
3. The screen of Claim 2 which comprises sheet means having only one forwardly facing surface and only one rearwardly facing surface, one of said lenticule arrays being formed on one of said surfaces and the other of said lenticule arrays being formed on the other of said surfaces.
4. The screen of Claim 2 wherein said respective cross-sectional shapes of said lenticules of said second array also vary as a function of their distance from said axis in such manner that, for each said viewing position within a selected second angular viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from said axis than is directed to that viewing position from those lenticules which are closer to said axis, so to at least partially compensate for the image light rearward reflection loss gradient;
said second array lenticule cross-sectional shapes being defined by a succession of lenticule profile elements;
the slope angle, length and position of each of said second array lenticule profile elements being determined by an algorithm which calculates the light transmission provided by each of said lenticule profile elements, and adjusts said slope angles, lengths and positions thereof to achieve said reflection loss gradient compensation.
said second array lenticule cross-sectional shapes being defined by a succession of lenticule profile elements;
the slope angle, length and position of each of said second array lenticule profile elements being determined by an algorithm which calculates the light transmission provided by each of said lenticule profile elements, and adjusts said slope angles, lengths and positions thereof to achieve said reflection loss gradient compensation.
5. The screen of Claim 4 wherein the lenticules on said rearwardly facing surface run substantially horizontally to distribute the image light over a vertical viewing range, and the lenticules on said forwardly facing surface run substantially vertically to distribute the image light over a horizontal viewing range which exceeds said vertical viewing range in size.
6. The screen of Claim 1 or 4, wherein said variation of cross-sectional shape as a function of distance from said axis is also such that a greater fraction of the incident image light is directed to a given viewing position from those lenticules which are further from said axis than is directed to that viewing position from those lenticules which are closer to said axis, so as to at least partially compensate for the cosine power fall-off of incident image light as a function of the angle of divergence relative to said axis.
7. The screen of Claim 1 or 4, wherein said variation of cross-sectional shape as a function of distance from said axis is also such that the angles of refraction of said lenticules are at least partially compensated for the greater angle of incidence of image light at greater distances from said axis, whereby to perform the collimating function of a field lens.
8. The screen of Claim 1 or 4, wherein said variation of cross-sectional shape as a function of distance from said axis is also such that a greater fraction of the incident image light is directed to a given viewing position from those lenticules which are further from said axis than is directed to that viewing position from those lenticules which are closer to said axis, so as to at least partially compensate for the cosine power fall-off of incident image light as a function of the angle of divergence relative to said axis, and said variation of cross-sectional shape as a function of distance from said axis is also such that the angles of refraction of said lenticules are at least partially compensated for the greater angle of incidence of image light at greater distances from said axis, so as to perform the collimating function of a field lens.
9. A method of manufacturing a projection screen for use with projection means located rearwardly of said screen for displaying an image to a plurality of observers located at viewing positions which are on the front side of said screen and dispersed in a direction parallel to said screen;
said projection means defining an axis;
said screen including at least one array of substantially rectilinear lenticules having respective light-refracting cross-sectional shapes adapted to redirect light arriving from the rear side of said screen so that an image formed on said screen by said light is visible at said dispersed positions;
said respective cross-sectional shapes of said lenticules varying as a function of their distance from said axis in such manner that, for each said position within a selected angular viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from said axis than is directed to that viewing position from those lenticules which are closer to said axis, so as to at least partially compensate for the image light rearward reflection loss gradient;
said lenticule cross-sectional shapes being defined by a succession of lenticule profile elements;
9. A method of manufacturing a projection screen for use with projection means located rearwardly of said screen for displaying an image to a plurality of observers located at viewing positions which are on the front side of said screen and dispersed in a direction parallel to said screen;
said projection means defining an axis;
said screen including at least one array of substantially rectilinear lenticules having respective light-refracting cross-sectional shapes adapted to redirect light arriving from the rear side of said screen so that an image formed on said screen by said light is visible at said dispersed positions;
said respective cross-sectional shapes of said lenticules varying as a function of their distance from said axis in such manner that, for each said position within a selected angular viewing range, a greater fraction of the incident image light is directed to that viewing position from those lenticules which are further from said axis than is directed to that viewing position from those lenticules which are closer to said axis, so as to at least partially compensate for the image light rearward reflection loss gradient;
said lenticule cross-sectional shapes being defined by a succession of lenticule profile elements;
Claim 9...continued.
said method comprising the steps of:
calculating the light transmission provided by each of said lenticule profile elements;
and adjusting the slope angle, length and position of each of said lenticule profile elements in a manner to alter said light transmission to achieve said reflection loss gradient compensation.
said method comprising the steps of:
calculating the light transmission provided by each of said lenticule profile elements;
and adjusting the slope angle, length and position of each of said lenticule profile elements in a manner to alter said light transmission to achieve said reflection loss gradient compensation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US222,836 | 1981-01-06 | ||
| US06/222,836 US4387959A (en) | 1981-01-06 | 1981-01-06 | Rear projection screen |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1167298A true CA1167298A (en) | 1984-05-15 |
Family
ID=22833903
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000390002A Expired CA1167298A (en) | 1981-01-06 | 1981-11-13 | Rear projection screen |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4387959A (en) |
| CA (1) | CA1167298A (en) |
Families Citing this family (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4536056A (en) * | 1981-10-05 | 1985-08-20 | Hitachi, Ltd. | Rear projection apparatus |
| US4512631A (en) * | 1983-04-21 | 1985-04-23 | Rca Corporation | Rear projection television screen incorporating a prism lens |
| JPH0721612B2 (en) * | 1986-07-25 | 1995-03-08 | 大日本印刷株式会社 | Lens sheet for transmission type projection screen |
| JPH0830848B2 (en) * | 1988-04-15 | 1996-03-27 | 株式会社日立製作所 | Multi-screen projector |
| US5448401A (en) * | 1992-12-25 | 1995-09-05 | Sony Corporation | Screen of projection display |
| JPH06205344A (en) * | 1992-12-29 | 1994-07-22 | Sony Corp | Video display device |
| KR100446223B1 (en) * | 1997-01-20 | 2004-11-20 | 다이니폰 인사츠 가부시키가이샤 | Transmissive screen |
| WO1999017159A1 (en) * | 1997-09-26 | 1999-04-08 | Koninklijke Philips Electronics N.V. | Image projection screen |
| JP3537309B2 (en) * | 1998-02-23 | 2004-06-14 | 大日本印刷株式会社 | Lens sheet for transmission screen and transmission screen |
| US6597502B2 (en) | 1998-02-23 | 2003-07-22 | Dai Nippon Printing Co., Ltd. | Rear projection screen with uniformity of luminance |
| US5902030A (en) * | 1998-05-29 | 1999-05-11 | Blanchard; Randall D. | System for displaying images from multiple projectors onto a common screen |
| US7697201B2 (en) * | 2006-05-24 | 2010-04-13 | Seiko Epson Corporation | Screen, rear projector, projection system, and image display unit |
| US7307790B1 (en) | 2006-11-10 | 2007-12-11 | Genie Lens Technologies, Llc | Ultrathin lens arrays for viewing interlaced images |
| US7414790B2 (en) * | 2006-11-10 | 2008-08-19 | Genie Lens Technologies, Llc | Ultrathin lens arrays for viewing interlaced images with dual lens structures |
| US7359120B1 (en) * | 2006-11-10 | 2008-04-15 | Genie Lens Technologies, Llc | Manufacture of display devices with ultrathin lens arrays for viewing interlaced images |
| US7480100B1 (en) | 2007-10-15 | 2009-01-20 | Genie Lens Technologies, Llc | Lenticular devices using sets of lenses to display paired sets of interlaces of images |
| USD735400S1 (en) * | 2013-02-09 | 2015-07-28 | SVV Technology Innovations, Inc | Optical lens array lightguide plate |
| CN116442629B (en) * | 2023-04-28 | 2024-01-26 | 深圳御光新材料有限公司 | Projection film and manufacturing method thereof |
Family Cites Families (28)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1942841A (en) * | 1931-01-19 | 1934-01-09 | Shimizu Takeo | Daylight screen |
| US1970358A (en) * | 1931-01-29 | 1934-08-14 | Electrical Res Prod Inc | Translucent optical projection screen |
| US2207835A (en) * | 1937-12-27 | 1940-07-16 | Thomas W Sukumlyn | Projection screen |
| US2338654A (en) * | 1942-04-08 | 1944-01-04 | Eastman Kodak Co | Projection screen |
| US2531399A (en) * | 1946-04-27 | 1950-11-28 | Farnsworth Res Corp | Television projection system and viewing screen |
| US2529701A (en) * | 1947-05-13 | 1950-11-14 | Rca Corp | Rear projection viewing screen |
| US2567654A (en) * | 1947-08-21 | 1951-09-11 | Hartford Nat Bank & Trust Co | Screen for television projection |
| US2618198A (en) * | 1947-11-22 | 1952-11-18 | Eastman Kodak Co | Projection screen |
| US2726573A (en) * | 1950-08-30 | 1955-12-13 | Rca Corp | Rear projection viewing screen |
| US3523717A (en) * | 1967-02-01 | 1970-08-11 | Gen Electric | Composite back projection screen |
| US3578841A (en) * | 1967-12-15 | 1971-05-18 | William B Elmer | Rear projection screen |
| US3580661A (en) * | 1969-04-10 | 1971-05-25 | Bell & Howell Co | Rear projection viewing screen for close viewing |
| US3712707A (en) * | 1970-02-27 | 1973-01-23 | Gen Electric | Composite back projection screen and method of forming |
| US3672894A (en) * | 1970-04-27 | 1972-06-27 | Gen Electric | Method for making a composite back projection screen |
| CA956819A (en) * | 1971-04-20 | 1974-10-29 | Kiyoshi Miyagi | Projection screen |
| US4078854A (en) * | 1971-10-05 | 1978-03-14 | Canon Kabushiki Kaisha | Stereo imaging system |
| BE792745A (en) * | 1971-12-15 | 1973-03-30 | Freen Ltd | TRANSPARENCY PROJECTION SCREEN |
| JPS5251538Y2 (en) * | 1972-04-25 | 1977-11-22 | ||
| US3782805A (en) * | 1972-11-30 | 1974-01-01 | Qantix Corp | Front projection screen made from a transparent material |
| US3846012A (en) * | 1973-11-14 | 1974-11-05 | Qantix Corp | Transparent front projection screen having concave ridges thereon |
| US3902787A (en) * | 1974-04-17 | 1975-09-02 | Action Films | Rear projection viewing screen |
| US3938876A (en) * | 1974-12-19 | 1976-02-17 | Qantix Corporation | Front projection screen made from a transparent material |
| US3966301A (en) * | 1974-12-19 | 1976-06-29 | Qantix Corporation | Transparent screen having intermittent portions for reducing reflection from ambient light |
| JPS583530B2 (en) * | 1975-02-28 | 1983-01-21 | ソニー株式会社 | rear projector armchair |
| DE2511390C2 (en) * | 1975-03-15 | 1984-03-15 | Agfa-Gevaert Ag, 5090 Leverkusen | Method and device for the production of daylight projection screens as well as daylight projection screen produced according to this method |
| DE2519617A1 (en) * | 1975-05-02 | 1976-11-11 | Agfa Gevaert Ag | PROJECTION SCREEN |
| US4012115A (en) * | 1975-07-10 | 1977-03-15 | Qantix Corporation | Sawtooth shaped front screen |
| US4165154A (en) * | 1976-10-05 | 1979-08-21 | Sanyo Electric Co., Ltd. | Projection screen assembly |
-
1981
- 1981-01-06 US US06/222,836 patent/US4387959A/en not_active Expired - Fee Related
- 1981-11-13 CA CA000390002A patent/CA1167298A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4387959A (en) | 1983-06-14 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |