EP1568216A1

EP1568216A1 - Method for electronic adjustment of the geometry in a videoprojector used in back projection and a videoprojector utilizing the method thereof

Info

Publication number: EP1568216A1
Application number: EP03777039A
Authority: EP
Inventors: Domenico Toffoli
Original assignee: SIM2 Multimedia SpA
Current assignee: SIM2 Multimedia SpA
Priority date: 2002-12-06
Filing date: 2003-12-04
Publication date: 2005-08-31
Also published as: WO2004054251A1; AU2003286296A1; ITTO20021069A1; TWI250374B; TW200419295A

Abstract

Method and videoprojector using such a method for adjusting the geometry of an image (2) produced starting from a digital video signal projected on a screen (1) by a videoprojector, in particular used in back projection, comprising the steps of: - entering a mode provided for electronic adjustment of the geometry of the image (2); - controlling, through control elements associated to the videoprojector, the electronic adjustment means that operate distortions on the digital video signal to be projected; to - bringing each apex of the image (2) to coincide with a respective apex of the screen (1) by means of the distortions operated by said electronic adjustment means on the digital video signal.

Description

METHOD FOR ELECTRONIC ADJUSTMENT OF THE GEOMETRY IN A VIDEOPROJECTOR USED IN BACK PROJECTION AND A VIDEOPROJECTOR UTILIZING THE METHOD THEREOF

DESCRIPTION

The present invention relates to a method for adjusting the geometry in a videoprojector, in particular used in back projection, as well as to a videoprojector utilizing such a method. The simultaneous use of mechanical miniaturization and technologies peculiar to semiconductors has led to the manufacture of small electromechanical systems, such as DMD (Digital Micromirror Device), LCD (Liquid Crystal Display), and LCoS (Liquid Crystal on Silicon), which are widely utilized in the manufacture of small light-weight videoprojectors ensuring excellent quality images. Videoprojectors can be used either in a frontal projection or back projection configuration, e.g. household maxi-screens, consisting of one single videoprojector or a so-called videowall, i.e. video walls formed by several back projectors arranged in a horizontal and vertical approach for obtaining a considerable large screen. In a back projector, the image is projected on a panel, such as a DMD device, focused by an optical system and sent either directly or by means of a mirror to a screen consisting of a Fresnel lens.

In frontal projection, both the user and light source are located on one same side with respect to the screen, whereas in back projection they are on opposite sides.

When the image formed on the panel is displayed on the screen, it is generally affected by geometric distortions, such as rotation around the vertical and/or horizontal axis, a vertical and/or horizontal trapeze, a wrong centering on the screen and either an excessive or poor size of said image. These distortions are basically due to various manufacturing frame tolerances of the back projection system, of the positioning device of the videoprojector, of the screen and relevant fastening, of the mirror position, of the lens-panel alignment of the videoprojector, etc. The most obvious effect of the above distortions is caused by the sides and apexes of the image rectangle, which do not coincide with those of the screen rectangle. In order to obtain a correct position of the image on the screen of a back projector, the videoprojector must be free to perform at least six adjustments, i.e. three shifts along the three orthogonal axis x y z, and three rotations, one around each axis x y z, respectively. Since the videoprojector is located on the opposite side of the screen with respect to the image being displayed, the image position has to be adjusted at least by two people, one person operating on the videoprojector manually at the back of the apparatus, e.g. tightening and/or loosening worm screws, the other giving useful adjustment instructions while looking directly at the screen. As a result, this is quite a complex operation demanding a long expensive performance, such as in the event of four or more videoprojectors needing adjustment, e.g. in the case of video walls. According to the Italian Patent IT1308864 the above drawbacks have been solved through implementation of a setup device with six independent mechanical adjustments actuated by motors and operated by means of a remote control, through which a single installer is able to adjust the image on the screen placing himself in front of it. However, this system based on mechanical adjustments has still some significant drawbacks, such as a high cost and the weight of the supporting base, which comprises three movable plates. Recently, other adjustment systems have been suggested, which are based on integrated circuits processing the image electronically, such as LEHK-3C of LIESEGANG ELECTRONICS and sxW1 of SILICON OPTIX. In order to obtain a satisfactory geometric correction of the image on the screen, these systems require several adjustments, which have to be repeated several times due to their being interdependent to each other, so that adjustment performance requires a long complex operation. It is the object of the present invention to provide a method for electronic adjustment of the geometry, particularly in back projection systems, which obviates to the above drawbacks and ensures a fast safe correct positioning of the image on the screen, with considerable shorter times and lower costs for adjustment operations.

A further object of the present invention is to provide a videoprojector for use in back projection, which utilizes the above adjustment method and has the same advantages. In order to achieve such aims, it is the object of the present invention to provide a method and a videoprojector incorporating the features of the annexed claims, which form an integral part of the description herein.

Further objects, features and advantages of the present invention will become apparent from the following detailed description and annexed drawings, which are supplied by way of non limiting example, wherein:

- Fig. 1 shows schematically the adjustment method of the geometry of the image projected on a screen, according to the invention;

- Fig. 2 shows a second embodiment of the adjustment method of the geometry of the image, according to the invention; - Fig. 3 shows a further embodiment of the adjustment method of the geometry of the image, according to the invention;

- Figg. 4a, 4b, 4c, 4d, 4e, 4f and 4g show a schematics of the possible intermediate steps used for adjusting the geometry of the image, according to the invention. According to the present invention, adjustment of the geometry of the image projected on a screen by a videoprojector used in back projection is obtained through the electronic processing of the digital signal of the image with the parameters acquired following an appropriate procedure as further described, in order to obtain its projection on the screen free of distortions and/or alterations. The peculiarity of the present adjustment method is based on the procedure being implemented, which ensures an immediate easy compensation of the distortion operating a restricted number of keys of the standard remote control provided with the product without requiring a particular capacity or special experience from the operator. Referring to Fig. 1 , reference 1 indicates a rectangular screen on which the image is projected by a videoprojector not shown here; reference 2 represents an image projected distorted on the screen 1 due to geometry distortions, as said distorted image 2 is projected with its apexes A', B', C, D' not coinciding with the relevant apexes A, B, C, D of the screen 1.

The adjustment method according to the present invention provides the following steps. First of all, a digital video signal is required.

Then the "Geometry Adjustment" mode of the videoprojector is entered according to common procedures, such as pressing a special key on the remote control or recalling the menu on the screen and scanning it with a cursor until "Geometry Adjustment" is reached. Pressing a special key on the remote control of the videoprojector, e.g. marked with the symbol "+" or writing "go on", the adjustment mode is operatively entered and a luminescent indication 3 consisting of one or more alphanumerical or graphic characters shows up near an apex of the image 1 , e.g. apex A' of Fig. 1 , instructing the operator where correction has to be started. Now, adjustment is performed actuating the directional keys High, Low, Right, Left, provided on the videoprojector or remote control, bringing the apex A' to coincide with the apex A of the screen 1 to a maximum extent. As said above, this is possible because the video signal is digitalized through a change circuit of the pre-distorted image form, so as to bring the apex A to coincide with the apex A.

Pressing the key + again, the luminescent indication 3 is displaced to another angle of the image, e.g. apex B', which is brought to coincide with the apex B actuating the directional keys as above. Also this adjustment is obtained by means of the distortions introduced by the above electronic adjusting means on the digital image to be projected.

Always using the key "+" and the four directional keys, the operation is repeated for the apexes C and D', which are brought to coincide with the apexes C and D, respectively. It should be noticed how in order to obtain the adjustments independently from each other and adjust the image only once for each apex, i.e. in one single operation cycle, the apexes must be corrected according to a predetermined order as directed by the luminescent indication 3. The circuit for deforming the digital image will in fact perform the subsequent distortions without altering the results of the previous distortions. Once the adjustment in the four apexes A, B, C, D, has been performed, the data related to said adjustment, i.e. the parameters for processing the image 2 and adapt it to the screen 1 are stored in a non volatile memory inside the videoprojector and they will be recalled for every subsequent activation of the videoprojector. Data storage may occur automatically when exiting the "Geometry Adjustment" mode or following an instruction from the operator. In order to perform optimal adjustments, the image 2 being formed on the screen 1 must be smaller than the active surface of the screen 1 itself; actually, should the image 2 have the same size of the screen 1 , a portion of its contents would fall out of the screen 1 when enlarging the image and go lost. The same drawback may occur when correcting a trapeze distortion, centering and rotation. Should a portion of the image 2 fall out of the screen 1 and be no longer visible as represented in the dotted area near the apexes C and D' of Fig. 1 , adjustment can be facilitated providing the image with appropriate indicating signals generated inside the videoprojector. To this purpose, four respective lines indicated with references a, b, c, d in Fig. 2 can be inserted parallel to each one of the four sides of the image. Should the apex C require adjustment, the keys would be actuated to increase the visible portion of the line a, whose dotted portion falls out of the screen. The four lines a, b, c, d may obviously also be joined to form a quadrilateral. Figg. 4a, 4b, 4c, 4d, 4e, 4f and 4g represent schematically the adjustments used for correcting the image 2 being formed on the panel for its subsequent projection on the screen free from distortions and alterations. The above adjustments are obtained processing the digital image of the panel, such as obtained with the DMD technology consisting of lines and pixel columns, according to known procedures as briefly recalled hereafter. For simplicity's sake the same references used for the projection of the image 2 on the screen 1 in Fig. 1 and 2 are maintained, even if the image process occurs at panel level, as said above. First of all, the apex has to be defined wherefrom the adjustment will start; in Fig. 4a, it has been arbitrarily chosen to start from the apex indicated with A'. Therefore, in Fig. 4a, the apexes indicated with A', B', C and D' represent the image 1 to be adjusted, which is displayed on the screen 2, whereas the apexes A, B, C and D represent the correct image desired, i.e. coinciding with the screen apexes. The apex A' is brought to coincide with the apex A operating a shift of the whole image, i.e. the positioning of the apex A' entails equal shifts for the apexes B', C and D'. In order to further facilitate the adjustment, these shifts can be partially compensated as illustrated hereafter. Since the apex A' has been chosen as the start point, all the following adjustments from Fig. 4b to Fig. 4g must occur in such a way so as to leave the position of the apex A' unchanged.

Fig. 4b is representing the horizontal bending, which leaves the positions of the apexes A and B unchanged and will shift the side comprised between the apexes C and D' horizontally.

This adjustment is obtained shifting the pixels that form the image horizontally: shifting changes linearly from a maximum for the pixels arranged on the side C- D' to zero for the pixels arranged on the side A-B. The Fig. 4c is representing the vertical bending, which leaves the positions of the apexes A and D unchanged and will shift the side between the apexes B' and C vertically. Adjustment is obtained shifting the pixels of the columns that form the image vertically: shifting changes linearly from a maximum for the pixels of the column coinciding with the side B'-C to zero for the pixels on the column placed on the side A-D. Fig. 4d is illustrating the horizontal perspective that leaves the apexes A, B and D unchanged and will shift the apex C horizontally. This adjustment is obtained by adding, i.e. interpolating, or detracting, i.e. reducing, pixels to or from the lines linearly from top to bottom: the line coinciding with the side A-B is not changed, whereas the line coinciding with the side C'-D is subject to a major pixel change.

Interpolation and detraction techniques are known in the handling field of digital video signals, so a detailed description is not required. Analogously, Fig. 4e is representing a vertical perspective leaving the apexes A, B and D unchanged and shifting the apex C vertically. In this event, pixels are added to, i.e. interpolated, or removed, i.e. detracted from the columns linearly from top to bottom: the column coinciding with the side A-D is not changed, whereas the column coinciding with the side B-C is subject to a major pixel change.

Fig. 4f is representing a change of the horizontal dimension of the image, which is obtained increasing, i.e. interpolating (for the enlargement) or decreasing, i.e. detracting (for the reduction) one same number of pixels for each line of the image, but maintaining a fixed starting line, so that the side between the apexes A and D is not shifted.

Finally, Fig. 4g is representing a change of the vertical dimension of the image, which is obtained increasing, i.e. interpolating (for the enlargement) or decreasing, i.e. detracting (for the reduction) one same number of pixels for each column of the image, but maintaining a fixed starting line at the top, so that the position of the apexes A and B remains unchanged. As mentioned above, the adjustments of the Figg. 4b, 4c, 4d, 4e, 4f and 4g leave unchanged the position of the apex A chosen for starting the adjustment. Obviously, should a different starting apex be chosen, the adjustments of the Figg. 4b, 4c, 4d, 4e, 4f and 4g would be appropriately changed, in order to avoid interaction with the position of the chosen apex.

As a first adjustment step, the apex A' is shifted to its correct position A actuating the shift as illustrated in Fig. 4a; this adjustment entails, as said above, a movement of the other three apexes. The apex B' adjacent to A' is brought to the position B using the vertical bending of Fig. 4c for the vertical shift and horizontal enlargement of Fig. 4e to shift it in the horizontal direction. As said, the adjustment of the apex B' does not produce any movements of the apexes A and D, whereas it will shift the apex C. The apex D', also adjacent to A, is brought to the position D through the horizontal bending of fig. 2 for its horizontal shift, and the vertical enlargement of Fig. 4g for its vertical shift. Adjustment of the apex D does not produce any shift for the apex B, but it will shift the apex C. Finally, the apex C\ opposite to the starting apex A', is brought to the position C using the horizontal perspective of Fig. 4d for its horizontal shift and the vertical perspective of Fig. 4e for its vertical shift. Adjustment of the apex C does not produce any effect to the other apexes. Therefore, when performing adjustment of the apexes in the following order: 1 ) pre-selected apex, in the example A'

2) apexes B' and D' adjacent to A'

3) apex C opposite to A' the adjustment of the geometry of the image is corrected performing one single adjustment to each apex, since the adjustment of one apex does not affect the position of the apexes previously adjusted. Since the apexes B' and D' have an equivalent effect on the position of the other apexes, it is irrelevant whether adjusting one first and then the other. However, the adjustment of an apex involves a movement of the apexes to be subsequently adjusted; therefore, a partial movement compensation can be introduced for the apexes subsequently adjusted to remain basically unmoved when adjusting an apex. In particular, when the apex A' is shifted, all apexes B', C and D' undergo a practically equal shift contrary to the one applied to the apex A', thus remaining nearly still; analogously, the adjustment of the apex B' produces an equal shift contrary to the apex C; the same applies for the adjustment of the apex D'. Practically, while performing this compensation the operator will only see the movement of the apex being adjusted, which simplifies his task further. It is obvious that many changes can be made to the adjustment method as well as to the videoprojector using such a method object of the present invention, without departing from the novelty principles of the inventive idea. For example, as represented in Fig.ure 3, indication of the apex to be corrected can be obtained by means of a small quadrilateral indicated with reference 4, in which the angle of interest is pointed out by a luminescent reference 5. If the quadrilateral 4 is placed in a central area of the image 2, indication of the apex to be corrected will never fall out of the screen, i.e. it is always visible, making the adjustment easier.

Indication of the apex to be corrected may also be in writing, such as "upper right angle", "lower left angle", and so on. The adjustment method described above may also be implemented in videoprojectors not used in back projection. The simple method adopted is in fact advantageous also for use in videoprojectors having a frontal configuration.

* * * * *

Claims

1. A method for adjusting the geometry of an image (2) produced starting from a digital video signal projected on a screen (1 ) by a videoprojector, in particular used in back projection, comprising the steps of:

- entering a mode provided for electronic adjustment of the geometry of the image (2);

- controlling, through control elements associated to the videoprojector, the electronic adjustment means that operate distortions on the digital video signal to be projected;

- bringing each apex of the image (2) to coincide with a respective apex of the screen (1 ) by means of the distortions operated by said electronic adjustment means on the digital video signal.

2. A method for adjusting the geometry according to claim 1 , characterized in that the adjustment parameters for each apex are stored in a non volatile memory and used at every subsequent activation of the videoprojector.

3. A method for adjusting the geometry according to claim 1 , characterized in that the distortions introduced by said electronic adjustment means on the digital video signal bring each apex of the image (2) to coincide with a relevant apex of the screen (1 ), operating only once for each apex according to a predetermined order.

4. A method for adjusting the geometry according to claim 1 , characterized in that the adjustment angle in the image (2) is indicated by one or more alphanumeric characters.

5. A method for adjusting the geometry according to claim 1 , characterized in that the adjustment angle in the image (2) is indicated by one or more graphic characters.

6. A method for adjusting the geometry according to claim 4 or 5, characterized in that said characters are placed near the apex to be adjusted.

7. A method for adjusting the geometry according to claim 1 , characterized in that said adjustment means comprise four instructions.

8. A method for adjusting the geometry according to claim 7, characterized in that said instructions are sent to the videoprojector by means of a remote control.

9. A method for adjusting the geometry according to claim 1 , characterized in that the image (2) contains signals being generated inside the videoprojector, being apt to facilitate the adjustment.

10. A method for adjusting the geometry according to claim 9, characterized in that said signals consist of lines parallel to the sides of the image (2).

11. A method for adjusting the geometry according to claim 1 , characterized in that the videoprojector utilizes DMD (Digital Micromirror Device) technology.

12. A method for adjusting the geometry according to claim 1 , characterized in that the videoprojector utilizes LCD (Liquid Crystal Display) technology.

13. A method for adjusting the geometry according to claim 1 , characterized in that the videoprojector utilizes LCoS (Liquid Crystal on Silicon) technology.

14. A method for adjusting the geometry according to claim 1 , characterized in that the adjustment apex is indicated by an alphanumeric or graphic signal placed near the center of the image.

15. A videoprojector, in particular used in back projection, characterized in that the adjustment of the geometry is performed according to the method of one or more of the previous claims.