US2301254A - Stereoscopic method and apparatus - Google Patents

Description

NOV. 10, 1942. c w C R STEREOSCOPIC METHOD AND APPARATUS Filed July 7, 1958 4 Sheets-Sheet l IN V EN TOR.

BY ATTORNEY .Nov. 19, 1942. c w CARNAHAN STEREOSGOPIC METHOD AND APPARATUS Filed July 7, 1958 4 Sheets-Sheet 2 INVENTOR.

Nov. 10, 1942. c. w. CARNAHAN Nml. 10), 1942. c w CARNAHAN 2,301,254

STEREOSCOPIC METHOD AND APPARATUS Filed July 7, 1958 4 Sheets-Sheet 4 WWW WWW

IN V ENTOR.

BY %F iaA ATTORNEY Patented Nov. 10, 1942 2,301,254 s'raanoscorro METHOD AND APPARATUS Chalon W. Carnahan, St. Marys, Pa., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application July 7, 1938, Serial No. 217,866

22 Claims.

This invention relates to stereoscopic systems and more especially to systems for projecting or reproducing images stereoscopically.

A principal object of the invention is to provide a method of recording and receiving a stereoscopic view of a televison subject on a single surface.

Another principal object of the invention is to provide an improved television reproducing screen for reproducing television images stereoscopically or with apparent relief.

A feature of the invention refers to an improved method and apparatus for scanning a televised scene or subject.

Another feature of the invention relates to a television reproducing screen made up of a phirality of strips of dichroic polarizing material, alternate strips acting on the light passing therethrough to polarize it at right angles to the polarization of the light passing through the intervening strips.

Another feature relates to a television system comprising a line structure of metallic coating On adjoining surfaces of two prisms joined together by a cement of the same refractive index as that of the material of which the two prisms are made.

A further feature relates to a method of reproducing or projecting a stereoscopic television image on a large screen.

A still further feature relates to the novel organization, relative location and interconnection of parts whereby an improved stereoscopic tele- Vision system is produced.

Other features not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention will be disclosed herein as embodied in a typical television system applying cathode-ray tubes with or without the application of intermediate films, it will be understood that this is done merely for explanatory purposes and not by way of limitation. Accordingly other well-known forms of television methods, as the supersonic wave method or mechanical methods with rotating or vibrating mirrors or with perforated discs may be adapted to the application of the invention.

In the drawings, Fig. 1 represents an improved method of providing alternate operating and off voltages for two television transmitting cathoderay tubes according to one feature of the invention.

Figs. 2, 3 and 4 are wave diagrams explanatory of the method of operation of certain parts of Fig. 1. I

Fig. 5 is a schematic diagrammatic representation of a television reproducing arrangement according to the invention.

Fig. 6 illustrates the method of making the dichroic screen made up of strips polarizing the transmitted light alternately inplanes parallel and at right angles to the direction of the strips.

Fig. '7 shows a method of recording two stereoscopic views of the same scene or object at the transmitting end, either on a photoelectric screen of a cathode-ray transmitting tube or on an intermediate moving picture film.

Fig. 7a is an enlarged view of part of Fig. 7.

Fig. 8 shows an alternate method of reproducing a stereoscopic picture of a televised scene or subject adapted to the use of a television projection system.

Fig. 9 illustrates the method of applying either sequential or interlaced scanning in connection with the invention.

The record of the original image may be produced either on a film or on the photo-sensitive cathode of an iconoscope or an image dissector.

Fig. 7 shows one preferred method of forming this record for television transmission. A coating of metallically reflecting lines 65 is deposited on the surface of prism 59. The part of the recording system shown in the figure acts as a synthesizer on recording surface 64, of the two stereoscopic views of the object 54 as seen by the objective lenses 55 and 56. Surface 64 may be either a photographic film or the screen of an "iconoscope or similar television scanner. The light rays L entering through objective 55 are totally reflected at surface 66 of prism 51 and a part L1 is reflected by the metallized line structure 65 on prism 59 through the end surface 61 of prism on to the recording surface 64. The prisms 59- and 60 are cemented together by a transparent cement of the same refractive index as that of the glass of which the prisms themselves are made. Therefore, that part of the light rays L2 which passes between the metal strips is not reflected but passes through in.

the direction it arrived at the surface 65 until it meets the wall 63 of prism 59. Here th light rays L; are absorbed by the black coating 63. The light rays L1 arriving at the recording surface 64 reflected by the metallic line structure produce an image of a line structure similar and parallel to that on surface 60.

The space left between theilluminated lines just described is filled in on recording surface 64 by that part R1 of the light rays R entering through objective 56 from the object 54 in a way similar to that explained in detail for the light rays L. In this way the two views as seen by the two objectives are projected on the surface 64 as an interleaved line structure.

If the recording surface 64 is the light sensitive screen of a cathode-ray tube the line structure is scanned, preferably but not necessarily by the interlaced scanning method.

An arrangement similar to the one described above is used, according to the invention, in reproducing at the receiving end, say for projection from a projection type cathode-ray tube. The interleaved image at the fluorescent screen of this tube is first separated by the prisms into the two original images, the separated images are transmitted through two dichroic filters, which are oriented at right angles to each other with respect to their polarizing properties, then combined again at the viewing screen in the same interleaved manner as explained above for the recording. The large screen picture obtained in this manner is observed by the audience by means of spectacles 5| (Fig. 5), in which dichroic screens polarizing at right angles to each other admit to each eye only the correlated image of the interleaved surface on the screen, which is proper for the respective eye for producing the stereoscopic view of the original scene. Fig. 8 illustrates the projection stereoscopically from an intermediate film record similar to the record 64 (Fig. 7). The rectangle R. in this figure represents schematically the apparatus of Fig. 7. Light from the source 68 is made parallel by the lens 69 and passed through the film 10 on which the interleaved positive picture of the original subject or scene is printed. The light rays passing through the set of alternating strips on the film on which, say, the view of the object 54 as seen by the objective 55 is printed, is guided by prisms I9, 80 and 11 through lens I2 and dichroic screen N, which has the proper orientation with respect to its polar properties corresponding to the orientation of one of the dichroic screens, say, 52 of the spectacles worn by the observers. The strip picture projected with light polarized by dichroic screen 14 arrives at the projection screen 16. The light passing through theother set of strips in the film is guided similarly by prisms I9 and 18 through lens 13 and dichroic filter 15 to the viewing screen 16. The polar orientation of the filter I5 is at right angles to that of filter 14. In this way the image at the screen 16 is built up of bands or strips of which one set of alternate ones reflects light polarized at right angles to that of the other set of strips. The distribution of the two sets of polarized images between the right and left eye of the observer is finally carried out by the dichroic screens .52 and 53 in the goggles as described above. The screen 16 is preferably of such material and surface structure by reason of which the polarization of the reflected light is substantially maintained in the same plane as the incident light, at least for reflection through an angle of about 20 degrees from the normal to the surface of the screen.

For reception on a direct viewing fluorescent screen, an alternate method is used according to the invention, in which the fluorescent screen on the cathode-ray receiving tube is equipped with a dichroic filter, make up of parallel stripes, passing alternately, horizontally and vertically polarized light. The manufacture of this type of striped'filter will be described later.

Either sequential or interlaced scanning may be applied in connection with the described system of stereoscopic television. The scanning at the transmission end must follow the lines of the image produced by the two objectives. At the receiving end, it has to follow the lines of the striped dichoric filter, in case of cathode-ray tube projection or direct viewing cathode-ray tube for reception, the scanning corresponding to the one used in transmission is applied in the exposure of the positive film.

The choice between the two systems of scanning is immaterial in the systems described above, and the selection between the two may be made according to convenience. Interlaced scanning is preferred, according to the invention, if it is desired to record the two images at the transmitting end with two cathode-ray transmitting tubes rather than with one. The application of two tubes in place of one may be advantageous at the transmitting end with the light available from the original scene or subject to be televised is very weak.

In the system described above, viz. in the "prism system with the metallically reflecting line coating, more than half the light that is available for transmitting is lost in the prism system. As explained in detail above, this is due to the fact that in addition to the losses from rejecting one half of the light arriving at the metal coated line structure, there are losses in the glass prism due to absorption and some reflection at the intersurfaces.

As is well known, the two stereoscopic views of an object may be taken on two entirely separated surfaces, as is usually done in conventional stereoscopic photographs, say, side by side. When this principle is transferred to the two mosaic screens of, say, two iconoscopes, it is evident that means have to be provided to alternately bias the two iconoscopes for oil and on operating conditions. The alternating bias which must be provided must be a very good approximation to a rectangular time voltage curve, as the reproduced picture will otherwise show an undesirable increase of brightness along the lines. Furthermore, there is a maximum frequency which can be transmitted by any transmission and amplifier system, and it is, therefore, desirable, to employ the lowest available frequency for the fundav mental frequency of the rectangular voltage time curve. If this is done, the approximation to the rectangular shape of this curve is relatively better than with any higher fundamental frequency, because of highest frequency which can be passed by the system is a higher harmonic of the fundamental. As is well known from the theory of Fourier series, a sharp change in direction requires these high harmonics.

reception. If a second intermediate film i used (is In the arrangement, according to the invention cribed below, these two requirements are fulfilled by using a multivibrator and by the application of interlaced scanning.

manner, it .is preferred, in accordance with the invention, to employ a pair of grid-controlled tubes which are arranged to pass platecurrent at regularly recurrent spaced intervals, one tube being blocked while the other tube is passing current.

Thus as shown in Fig. 1, the television impulses generated by dissector l are applied to the control-grid 4 of a suitable grid-controlled tube-5 which is preferably, although not necessarily, of the screen grid type comprising an electronemitting cathode 6, a control-grid t, a shieldgrid 1 and a plate electrode 8. Likewise the television impulses from dissector 2 are applied to the control-grid 9 of a similar grid-controlled tube ill having an electron-emitting cathode H, a control-grid 9, a shield-grid l2, and a plate electrode E3. The grid l is connected to cathode 6 through the grid-biassing resistors M, It and thence to ground through the steady D. C. biassing source it, it being understood that the oathode 6 is grounded as indicated. A similar gridbiassing circuit is provided for tube ill traceable from the grid 9 through bias resistors ll, 88,

biassing source it to ground, the cathode i i likewise being grounded. The plate electrodes ii and i3 are connected to a suitable source of a steady plate potential it through. a resistor 20. The shield-grids i and i2 are connected to an intermediate point of the D. 0. supply source l9 through suitable resistors 2 i 22 in the wellknown manner. The parameters of the above described grid-biassing circuits for each of the tubes 5 and iii, are chosen so that normally both tubes are classed to their plate current cut-off. In order to render the tubes 5 and lil alternately effective in passing plate current, there is provided a pair of grid-controlled tubes 23, 2t, which are interconnected with a source of alternating current 25 by a multivibrator circuit arrangement. For this purpose, the plate electrodes 26,27, are connected through their individual resistors 28, 29, to a source of steady plate potential 30. The control-grids M, 32, are connected to their respective cathodes 33, 34 through leak resistors 35, 36. The plate 25 is connected through condenser 37 to control-grid 32 and plate 2! is likewise connected through condenser 38 to control-grid M. The controLgrid Si is also connected through condenser 39 to the alternating current source 25.

In case of sequential scanning as distinguished from interlaced scanning, source 25 may be synchronized with the line frequency of dissector l and 2 so that source 25 produces a signal at onehalf of the line scanning frequency. The plate 26 of tube 23 is connected through condenser 60 to a point between the resistors l t and It. Likewise the plate 25 is connected through condenser ii to a point between the resistors ll and 88. By reason of the multivibrator connection between the source 25 and the tubes 23, 24, these latter tubes are alternately effective in passing plate currents. In other words, the voltage conditions on the plates 23 and 21 are 180 out of phase as represented respectively by the curve A of Fig. 2 and the curve B of Fig. 3 and the frequency of the waves A and B is one-half of the line scanning frequency represented by curve of Fig. 4. Consequently, the potential of the points i2, 43, will likewise be 180 out of phase. Likewise, the biassing potential on the grids 6 and 9 at any given instant, will be determined by the biassing circuits above described as well as by the potential applied through the condensers M, M. Therefore when grid 8 is biassed below cut-off, the grid 9 is biassed above cut-off. Consequently tube 5 will pass the amplified television currents from dissector I to the amplifier M during a given I scanned line of the subject 3, and when the next 7 line of the subject 3 is scanned by device 2, the tube i0 is blessed below cut-off and the tube 5 is blessed above cut-01f so that the amplified output of tube alone is applied to the amplifier it. By this arrangement therefore, the devices 1 and 2 can scan the subject 3 continuously, however, the impulses from the devices I and 2 are alternately eflective in controlling the amplifier 34 and since the alternations are synchronized with the line scanning frequency, the net result is that one linear element of the subject 3 is scanned and its response is amplified by tube 5, the next linear element is scar'med by device 2 is amplified by tube l0, and so on until all the linear elements of the subject are scanned. It will be understood of course that the television scanners are adjustable so that the width of the scanning spot of each scanner is equal to the width of each interleaved strip of'the stereoscopic record being scanned and the number of line scanning traverses of the scanners is equal in length and number to the length and number of each of the stereoscopic views of the record.

Preferably, and in accordance with the invention, source is synchronized by the frame frequency rather than by half the line frequency, and interlaced scanning is applied rather than sequential scanning. This insures, as explained above, an improved approximation to the rectangular shape of the voltage time curve for the ofi and operating bias of the two iconoscopes.

After suitable amplification in the amplifier M, the television currents may be transmitted over any well-known transmission channel such as a wire channel, a radio channel or the like to any well-known form of television receiver indicated schematically in Fig. 5 by the numeral 65. For the details of such a receiver, reference may be had to Fender and McIlwain, Electrical Engineers Handbook, third edition, V, l5-25, John Wiley 8; Sons, New York, 1936.

In the well-known manner, the output of the receiver is used to control the production of a light spot of varying intensity and this spot is moved over a suitable reproducing screen in synchronism with the scanning spots of the devices I and 2 at the transmitter. For purposes of iilustration, the device for producing the moving light spot in Fig. 5 is represented schematically by a cathode-ray tube 46 by means of which the received television currents are converted into the original image on the end wall or screen A! of the tube. Ordinarily, the image on the screen 41 would be viewed by an observer directly. In accordance with the present invention, the light image reproduced on screen M is projected or passed through another screen 68 made up of a plurality of successive linear strips 49, 50, of any well-known dichroic light polarizing material, such as for example as Polaroid. It will be understood of course that there will be the same number ofstrips 49, 50, as the number of linear elements scanned in the original subject.

The strips 69 and are arranged sothat alternate strips polarize the light passing therethrough at right angles, for example the strips 49 may be arranged to polarize horizontally the light passing therethrough, while the strips 50 polarize vertically the light passing therethrough. The observer views the screen 48 through a pair of dichroic light polarizing filters which may, for example be mounted in a'spectacle frame 5|. The filter 52 mounted in the left portion of the spectacle frame is arranged to pass light polarized in a horizontal plane, that is, the light passed by strips 49; while the filter 53 in the righthand part of the spectacle frame passes light polarized in the vertical frame, that is, the light passed by strips 50. It'will be understood of course, in accordance with well-known television principles, that the complete subject at ithe transmitter and at the receiver is scanned a certain minimum number of times per second in accordance with the persistency of vision, for example, the subject may be scanned completely sixty times per second. Consequently, the observer viewing the screen 48 through the filters 52, 53, sees the image first through one eye and then through the other. Because of these displaced images, corresponding to the 'scannings by devices I and 2 at the transmitter which are stereoscopically or angularly placed with respect to the subject 3, the observer is given the impression of depth or relief in the. image reproduced screen 43. It will be understood that the number of linear elements scanned and consequently the number of strips 49, 50, employed in the reproducing section are such that each alternate set of strips when' illuminated givea satisfactory complete image of the subject.

The dichroic screen 48 of which alternate strips 49 and 50 are passing light polarized parallel and at right angles respectively to the direction of the'strips may be made in a number of ways. A preferred way will now be described in connection with Fig. 6.

Generally, the proper orientation of the dichroicmaterial to secure a high and uniform degree of plane polarization of the transmitted light is accomplished by using some asym-.

. metrical property of the material to align the particles. If the asymmetry is one of physical dimensions, e. g. as in the crystals of herapathite, which are needle shaped, the unoriented crystal mass mixed in a viscous cellulosic matrix may be extruded through a long narrow tube causing the needle-like crystals to be aligned in the direction of the fiow lines of the matrix. If the asymmetric property is a large molecular magnetic or electric moment, the mixture of dichroic material and matrix either during or after deposition on the supporting base, is subjected to suitably directed magnetic or electric fields, whichinteract with the individual molecular moments to align the crystals in'the preferred direction with respect to the fields. Generally, dichroic materials show all of the above mentioned properties, and alignment by liquid fiow is to be preferred because of its greater convenience.

One way of making the screen 48 would be to cut e. g. the strips 49 parallel to the direction of flow of one sheet of dichroic material deposited on :Sat surface by the flow method described above. The strips 50 may then be cut out of another sheet at right angles to the lines of fiow. Finally alternate strips are cemented parallel to and touching each other on a suitable transparent carrier plate.

Considering the narrowness of the strips, which is of the order of .008" to .040", the cutting andcementing of a screen according to the described method may be inconvenient. According to the invention, therefore, one sheet 82 of the liquid dichroic material is deposited (see Fig. 6) on a suitable transparent matrix 8| provided with rectangular grooves of the desired width and distance between the grooves, from the nozzle 84. This sheet is deposited parallel to the direction of the grooves. A sheet 82 of periodically variable thickness viz. of the thicknesses AB and AC respectively is thus formed on the matrix 8|. Before or after the dichroic material has dried, the layer thickness AB is removed leaving the grooves 83 filled with the polarized material, while the strips between th grooves are free from,

dichroic material. The second half of the dichroic linear screen is made by depositing in a similar way on a matrix 8| dichroic material from an appropriate nozzle, this time, however, at right angles to the direction of the grooves in the matrix. After removing the excess material as before on the first half, the two halfscreens are cemented together in the manner indicated in Fig. 6.

What I claim is: V

1. In a stereoscopic system, means to form an interleavedstereoscopic record of an image com-' prising a prism having one,face provided with a plurality of spaced linear reflecting strips, means to form two separate sterecsccpic views of the image,- means to project one of said views on said prism face at such an angle that only spaced linear elements are reflected by said reflecting strips, and means to transmit the other of said views through the spaces between said strips, a receiving surface, and means to project upon said surface the reflected image strips and -the transmitted image strips to form a single interleaved strip stereoscopic image.

2. A system according to claim 1 in which television scanning means are provided to scan said interleaved image on said receiving surface.

3. A system according to claim 1 in which the said means on the said one of said prism faces consists of a series of spaced metallic reflecting strips.

4. A system according to claim 1 in which television scanning means are provided to scan said interleaved image and the width of the scanning spot of the television scanner is adjustable to the width of each of the interleaved strips of the image.

5. A stereoscopic system comprising a prism having alternate linear strips which are light transmitting and light reflecting, means to project upon said strips corresponding sets of light strips each set of light strips representing a corresponding stereoscopic spaced-strip image of a single subject whereby av single complete view of the subject is broken up into two simultaneous specially separated views each corresponding to one of said sets of light strips, and means to pass light simultaneously from said separate views through respective dichroic filters arranged to polarize in mutually perpendicular planes the light passing therethrough.

6. A stereoscopic system according to claim 5 in which the polarized light passed by said filters is projected on a screen having a surface whereby the light reflected therefrom is maintained in substantially the same polarized plane as the incident light at least for reflection through an angle of 20 degrees from the normal to the surface thereof.

7. A system according to claim 1 in which said receiving surface consists of a viewing screen, said screen having associated therewith dichroic polarizers for producing a single stereoscopic image on said screen with alternate strips having the light polarized in one plane and the intervening strips having the light polarized in a plane at right angles to said one 'plane.

8. In a stereoscopic system, means to form a single interleaved strip stereoscopic record repand passing the polarized lights through correresenting different stereoscopic aspects of an image comprising a pair of prisms having opposed surfaces cemented together by a cement I having the same refractive index as that of the prisms, means disposed on one of said cemented surfaces for composing an interleaved strip image of two separate stereoscopic views of a subject or scene, and means to project said single interleaved image on a receiving surface.

9. In stereoscopic television apparatus, means to form two separate images representing spaced stereoscopic views of a subject and to combine said views into a single interleaved strip view, a television scanner for scanning each of said interleaved strips, and means including a single television reproducer and a dichroic filter screen for reproducing said image stereoscopically. I

l0. Apparatus according to claim 9 in which the television reproducer includes the fluorescent screen of a cathode-ray tube.

11. In a stereoscopic apparatus comprising means for forming two separate stereoscopic views representing different aspects of a subject and combining them including a prism, having on one face' a series of spaced reflecting strips, means to project on said reflecting strips one of said separate views for reflecting only alternate lines, means to transmit only alternate lines of the other view through the spaces between the said reflecting strips, and a single receiving surface upon which the transmitted and reflected lines are simultaneously projected and interleaved to form a single image.

12. Stereoscopic apparatus including means to form on the photo-cathode of a cathode-ray tube television transmitting scanner a single stereoscopic interleaved strip image of a subject, means to scan said interleaved strip image to produce television currents representingthe two interleaved stereoscopic images and means to reproduce an image of the subject under control of said currents the last-mentioned means including a single cathode-ray receiving tube having a dichroic filter screen associated therewith, said fllter having interleaved strips corresponding to said interleaved strips of the original stereoscopic image certain of said filter strips polarizing light in one plane, and other of said strips polarizing light in another plane.

13. Stereoscopic television reproducing apparatus comprising a cathode-ray tube television receiver, a screen associated with said receiver comprising alternate strips of dichroic material each strip corresponding to a corresponding strip of the fluorescent screen of said tube and alternate strips polarizing light received thereby in a plane at right angles to the polarization of the light received by the intervening strips.

14. The method of electro-optical transmission which includes the steps of scanning a television scene to produce two series of current impulses representative of stereoscopic views of the subject, translating the currents into a corresponding television image, polarizing the light from alternate strips of said image in one plane and polarizing the light from the intervening strips in a diflerent plane, and passing said polarized light through corresponding polarized viewing filters.

15. The method of electro-optical transmission which includes the steps of projecting a received television image on a light polarizing screen to divide certain elements of the image into light polarized in one plane and to divide other elements into light polarized in a different plane.

sponding polarized filters.

16. Means for reproducing a television image stereoscopically comprising a screen upon which the television image is projected, said screen consisting of a plurality of sets of dichroic light polarizing members certain of said members polarizing in one plane light from corresponding areas of the image and other dichroic members polarizing light from other corresponding areas of the image in a difierent plane, and a pair of light filters, each filter passing light from only one of said sets of members.

1'7. The method of producing a stereoscopic image of a subject which includes the steps of producing on two separate reflectors separate complete images of the subject, reflecting said separate images on to a common reflector having alternate linear light reflecting and light transmitting strips, to produce a single composite stereoscopic image on a receiving surface which image consists of alternate interleaved linear strips.

18. The method of producing a stereoscopic image of a subject which includes the steps of projecting the image on to a surface having alternate linear light reflecting and light transmitting strips, passing the light reflected from the reflecting strips through a correspondingly polarized light filter passing the light transmitted by said light transmitting strips through another correspondingly polarized light filter, and projecting the lights passed by said filters in superposed relation on a receiving surface.

19. Apparatus for producing a stereoscopic image of a subject comprising means to produce two complete stereoscopic images of the subject, a prism having one of its faces provided with alternate linear light reflecting strips and light transmitting strips, means to project said complete images on said prism face so that the light from alternate strips of one of said complete images is reflected from said light reflecting strips and the light from the alternate strips of the other of said complete images is transmitted through said light transmitting strips, and a receiving surface upon which the reflected strips and transmitted strips are interleaved to form a single composite stereoscopic image.

20. Apparatus according to claim 19 in which said rism is formed of two prism sections having opposed surfaces together cemented together with a cement having the same refractive index as that of the prisms.

21. An arrangement for forming an interleaved stereoscopic image of a subject comprising a pair of prisms cemented together, the opposing face of one prism being rovided with spaced linear light reflecting strips, and means to project upon said face a single image representing spaced stereoscopic views of the subject.

22. The method of electro-optical transmission which includes the steps of scanning a television scene to produce television currents representing an interleaved-strip stereoscopic views of a subject, translating the currents into a corresponding television image, polarizing the light from alternate strips of said television image in one plane and polarizing thelight from the intervening strips of said television image in a different plane, and passing said polarized light from all of said strips through corresponding polarized viewing filters.

CHALON W. CARNAHAN.

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