Abstract:
A system for measuring the convergence alignment may include an optical system arranged to preferentially image and magnify the regions of a display screen outside the area normally viewed by users. That area may include convergence targets which may be associated with each corner of the display. That information may be provided as a unified image to an imaging sensor which may thereafter be utilized to analyze the information and if desired, make appropriate corrections.

Description:
BACKGROUND 
     The invention relates to aligning images of a projection system, such as a liquid crystal display (LCD) projection system, for example. 
     Referring to FIG. 1, a reflective liquid crystal display (LCD) projection system  5  typically includes an LCD display panel (LCD display panels  22 ,  24  and  26 , as examples) for each primary color that is projected onto a screen  10 . In this manner, for a red-green-blue (RGB) color space, the projection system  5  may include an LCD display panel  22  that is associated with the red color band, an LCD display panel  24  that is associated with the green color band and an LCD display panel  26  that is associated with the blue color band. Each of the LCD panels  22 ,  24  and  26  modulates light from a light source  30  to form red, green and blue images, respectively, that add together to form a composite color image on the screen  10 . To accomplish this, each LCD display panel  22 ,  24  or  26  receives electrical signals that indicate the corresponding modulated beam image to be formed. 
     More particularly, the projection system  5  may include a beam splitter  14  that directs a substantially collimated white beam  11  of light (provided by the light source  30 ) to optics that separate the white beam  11  into red  13 , blue  17  and green  21  beams. In this manner, the white beam  11  may be directed to a red dichroic mirror  18  that reflects the red beam  13  toward the LCD panel  22  that, in turn, modulates the red beam  13 . The blue beam  17  passes through the red dichroic mirror  18  to a blue dichroic mirror  20  that reflects the blue beam  17  toward the LCD display panel  26  for modulation. The green beam  21  passes through the red  18  and blue  20  dichroic mirrors for modulation by the LCD display panel  24 . 
     For reflective LCD display panels, each LCD display panel  22 ,  26  and  24  modulates the incident beams, and reflects the modulated beams  15 ,  19  and  23 , respectively, so that the modulated beams  15 ,  19  and  23  return along the paths described above to the beam splitter  14 . The beam splitter  14 , in turn, directs the modulated beams  15 ,  19  and  23  through projection optics, such as a lens  12 , to form modulated beam images that ideally overlap and combine to form the composite image on the screen  10 . 
     However, for purposes of forming a correct composite image on the screen  10 , the corresponding pixels of the modulated beam images may need to align with each other. For example, a pixel of the composite image at location ( 0 , 0 ) may be formed from the superposition of a pixel at location ( 0 , 0 ) of the modulated red beam image, a pixel at location ( 0 , 0 ) of the modulated green beam image and a pixel at location ( 0 , 0 ) of the modulated blue beam image. Without this alignment, the color of the pixel at location ( 0 , 0 ) may be incorrect, or the color may vary across the pixel. 
     At the time of manufacture of the system  5 , the LCD display panels  22 ,  24  and  26  typically are mounted with sufficient accuracy to align the pixels of the modulated beam images. One way to accomplish this is to approximate the correct position of the LCD display panels  22 ,  24  and  26  and thereafter use the LCD display panels  22 ,  24  and  26  to attempt to form a white rectangular composite image onto the screen  10 . If the LCD panels  22 ,  24  and  26  are not properly aligned, then red  42 , green  44  and/or blue  46  color borders may be detected around the perimeter of a white image  40  that is formed on the screen  10 , as depicted in FIG.  2 . However, when the LCD panels  22 ,  24  and  26  are properly aligned, the color borders  42 ,  44  and  46  do not appear, and an enlarged white image  40  appears on the screen  10 , as depicted in FIG.  3 . 
     Unfortunately, conventional techniques that are used to align the LCD display panels  22 ,  24  and  26  may consume a considerable amount of time in the manufacture of the projection system  5 . Furthermore, such factors as aging and thermal drift may cause the LCD displays panels  22 ,  24  and  26  to fall out of alignment during the lifetime of the projection system  5 . 
     Thus, there is a continuing need to address one or more of the problems stated above. 
     SUMMARY 
     In one embodiment, a system for measuring convergence alignment of a projected image of a projection display includes an optical system adapted to create separate images of at least two spaced locations on the projected image. An image sensor is arranged to capture the separate images. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an LCD projection system of the prior art. 
     FIG. 2 is an illustration of images formed by LCD display panels of the system of FIG. 1 when the display panels are not aligned. 
     FIG. 3 is an illustration of an image formed by LCD display panels of the system of FIG. 1 when the display panels are aligned. 
     FIG. 4 is a schematic depiction of a projection system in accordance with one embodiment of the present invention. 
     FIG. 5 is a front elevational view of the screen shown in FIG.  4 . 
     FIG. 6 is a perspective view of one embodiment of the prism that may be used in the embodiment shown in FIG.  4 . 
     FIG. 7 is a view corresponding to the image received by the sensor in the embodiment shown in FIG.  4 . 
     FIG. 8 is a schematic diagram of a light valve according to an embodiment of the invention. 
     FIGS. 9,  10  and  11  are illustrations of alignment scenarios between two modulated beam images that are formed by display panels of the projection system of FIG.  8 . 
     FIG. 12 is an illustration of a display panel according to an embodiment of the invention. 
     FIG. 13 is an electrical schematic diagram of the projection system of FIG. 4 according to an embodiment of the invention. 
     FIG. 14 is an illustration of a portion of a pixel map. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 4, an image capturing system  400  is incorporated into a projection display  402 . The projection display  402  may be of any form. For example, in one embodiment of the present invention, a light valve  404  may receive input video and project that video through a projection lens  57  onto a folding mirror  408  which reflects the image onto a projection mirror  410  and then onto a screen  59 . The images projected onto the screen  59  are viewable from outside the housing  420 . 
     The image capturing system  400  includes a digital sensor  414  which may be a complementary metal oxide semiconductor (CMOS) sensor or another digital sensor such as a charge coupled device (CCD) sensor. The image capturing system also includes a lens  416  and optical system  418 . The optical system  418  is adapted to selectively capture an image of the portions of the screen  59  proximate to convergence targets positioned outside of the viewable portion of the display. 
     In one embodiment, the screen  59  may be mounted into the housing  420  so that all the user sees is the housing and a portion of the projection screen  59 . Viewable only from inside the housing  420 , are convergence targets  425 , as shown in FIG.  5 . The convergence targets  425  may be of a variety of conventional types. They may be situated outside the viewable display portion  426  in the peripheral region  428 . The peripheral region  428  is hidden from a user outside the housing  420  due to the intervention of a portion  421  of the housing  420  which covers the outside surface of the region  428 , as shown in FIG.  4 . 
     Each target  425  may provide information about the convergence of the displayed color planes. In a sense then, the convergence targets are test patterns for measuring convergence alignment of the display. They may have images on them or they may simply receive samples of the light from the display. 
     Referring to FIG. 6, the optical system  418  may include a pyramidal prism  424  including four sides  422 . Each side or facet  422  is optically aligned with one of the convergence targets  425  in one embodiment of the invention. Thus, in one embodiment, each facet preferentially captures an image of each corner of the display screen  59  including a convergence target  425 , and further including adjacent portions of the peripheral region  428  outside of the viewable portion  426 . 
     Referring to FIG. 7, an example of an image  401  captured by the image capturing system  400  is illustrated. It includes magnified versions  425   a  of the convergence targets  425  together with proximate quadrants  426  of the display actually viewed by the user. Since it captures the convergence targets  425 , the system  400  also captures portions of the region  428  not viewable by the user which include the target  425 . In this way, magnified images of the corner regions may be obtained so that the resolution of the imaging sensor  414  is conceptually moved to the corners. A plus-shaped region  430 , shown in FIG. 5, may be excluded from the image  401  to improve the resolution of the convergence targets  425 . 
     The imaging system  400  need not correct for chromatic aberration since all that is desired is to determine the degree and direction of chromatic aberration. The lens  416  may provide sufficient magnification so that more than one sensor pixel is associated with each projected pixel of interest. This improves the resolution of the location of each of the three color planes. As a result, it is easier to determine if there is misalignment. 
     The sensor  414  may include a color filter array (CFA) to separate the colors. The convergence pattern contribution of the red color stimulates the red CFA color pixels and so on. Post processing of the color data provides information for correction of chromatic aberration and provides the actual displacement of each color about the beam or about a reference color. 
     Once the displacement has been measured, electromechanical, optical, electronic or any other means may be used to provide convergence alignment. Imaging each of the four corners allows a highly accurate determination of offset, tilt and magnification errors. 
     In embodiments which are contained essentially in a housing as illustrated, focus adjustments for the optics system  400  may be unnecessary since the distances are all fixed. Thus, the system continues to monitor the convergence targets during an initial set-up phase and thereafter to accurately sense any convergence errors which may arise, in one embodiment of the invention. In other embodiments focus adjustments may be applied as needed. 
     While a variety of different techniques may be utilized to correct any convergence errors that are detected by the system  400 , an example of one technique is described hereinafter. This does not in any way suggest or imply that the present invention is in any way limited to any specific technique for correcting convergence errors. 
     More particularly, FIG. 9 illustrates two modulated beam images  63  and  65 , each of which is formed by a different display panel  60  of the light valve  404  modulating an incident beam of light of a particular color band. Each pixel  67  of the beam image  63  is located approximately ½ pixel from the corresponding pixel  67  of the beam image  65 , i.e., the beam images  63  and  65  are “½ pixel” out of alignment. Thus, the pixel  67  at location ( 0 , 0 ) of the image  65  is approximately ½ pixel away from the pixel  67  at location ( 0 , 0 ) of the image  63 . To cause the two beam images  63  and  65  to converge, actuators  62  (see FIG. 8) may be used to reposition the display panel  60  that generated the beam image  63 , reposition the display panel  60  that generated the beam image  65  or reposition both of the display panels  60 . As illustrated, the rows (and columns) of pixels  67  of the beam image  63  are parallel to the rows (and columns) of pixels of the beam image  65 . Thus, translational movement (and not rotational movement, described below) of one or more display panel(s)  60  may be used to cause the beam images  63  and  65  to converge. 
     In some embodiments, the actuators  62  may be used to perform a maximum alignment of up to approximately one pixel, hereinafter called a fine, or local, adjustment, for purposes repositioning display panel(s) to align the boundaries of pixels. However, before calibration, some modulated beam images may be located further apart, as illustrated in FIG.  10 . For example, a pixel  67  at location ( 0 , 0 ) of a modulated beam image  71  may be located several pixels away from a pixel at location ( 0 , 0 ) of a modified beam image  69 . For this scenario, in some embodiments, the actuators  62  may be used to locally align the beam images  69  and  71  so that the pixels (regardless of their locations) of the beam images  69  and  71  are locally (but not globally) aligned. For example, due to this local alignment, the pixel at location ( 3 , 3 ) of the beam image  69  may be aligned with the pixel at location ( 0 , 0 ) of the beam image  71 , i.e., the boundaries of the pixels are aligned. 
     In some embodiments, coarse, or global, alignment may be performing by remapping pixels of one or more display panels  60 , as described below. This remapping, in turn, may align the pixel at location ( 0 , 0 ) of the beam image  71 , shown in FIG. 10, by remapping pixel locations of the display panel that forms the beam image  69 , for example. For this to occur, extra pixels (also called “pixel cells” or “pixel elements”) of the display  60  that forms the beam image  69  may be used. 
     As an example, for a desired resolution of 1024 horizontal pixels by 768 vertical pixels (i.e., for a 1024×768 display), the display panel  60  may have 1034 horizontal pixels by 778 vertical pixels, i.e., ten extra pixels in both the vertical and horizontal directions. In this manner, a block  75  (FIG. 12) of the pixels may be active and thus, may be used to form the modulated beam image. The remaining pixels  77  may be inactive, or permanently turned off, due to the application of a mapping function to correct global misalignment. To accomplish this, the mapping of the pixels on the display panel  60  are adjusted accordingly to shift the block  75  of active pixels horizontally, vertically or in both directions. 
     Thus, in FIG. 10, the pixels of the display  60  that generated the beam image  69  may be remapped so that the pixels of the display that form pixels  67  of the beam image  69  that do not globally converge with the beam image  71  are turned off. Therefore, the pixels of the display panel  60  that form the beam image  69  may be remapped to effectively shift the block of active pixels of the display panel  60  down by four rows and to the right by three columns to globally align the beam images  69  and  71 . 
     Referring back to FIG. 8, in some embodiments, the light valve  404  may include prisms  52  (prisms  52   a ,  52   b ,  52   c  and  52   d , as examples) that direct an incoming beam of white light (formed from red, green and blue beams) from a light source  63  to the display panels  60 , as described below. In particular, the prism  52   a  receives the incoming white beam of light at a prism face  52   aa  that is normal to the incoming light and directs the beam to a prism face  52   ab  that is inclined toward the face  52   aa . The reflective face of a red dichroic mirror  54   a  may be mounted to the prism face  52   ab  or to the prism face  52   ca  by a transparent elastomeric adhesive layer  56   a  that aids in positioning the display panels  60   b  and  60   c , as further described below. 
     The red dichroic mirror  54   a  separates the red beam from the incoming white beam by reflecting the red beam so that the red beam exits another prism face  52   ac  of the prism  52   a  and enters a prism face  52   ba  of the prism  52   b . The prism faces  52   ac  and  52   ba  may be mounted together via a transparent elastomeric adhesive layer  56   c  that aids in positioning the display panel  60   a . The prism  52   b , in turn, directs the red beam to the incident face of the display panel  60   a  that is mounted to another prism face  52   bb  of the prism  52   b  that is inclined toward the prism face  52   ba . The display panel  60   a  modulates the incident red beam, and the modulated red beam follows a similar path to the path followed by the incident red beam. However, instead of being directed toward the light source  63 , a beam splitter  55  directs the modulated red beam through projection optics  57  (a lens, for example) that forms an image of the modulated red beam on a screen  59 . 
     The remaining blue and green beams (from the original incoming white beam) pass through the red dichroic mirror  54   a . The opposite face of the mirror  54   a  is attached to a prism face  52   ca  of the prism  52   c , an arrangement that causes the blue and green beams to pass through the red dichroic mirror  54   a , pass through the prism face  52   ca  of the prism  52   c , travel through the prism  52   c  and pass through a prism face  52   cb  (of the prism  52   c ) that forms an acute angle with the prism face  52   ca . The reflective face of a blue dichroic mirror  54   b  is mounted to the prism face  52   cb  or to the prism face  52   da . As a result, the blue dichroic mirror  54   b  reflects the blue beam back into the prism  52   c  to cause the blue beam to exit another prism face  52   cc  of the prism  52   c . The incident face of the display panel  60   b  is mounted to the face  52   cc  and modulates the incident blue beam. The modulated blue beam, in turn, follows a path similar to the path followed by the incident blue beam. The beam splitter  55  directs the modulated blue beam through the projection optics  57  to form an image of the modulated blue beam on the screen  59 . 
     The green beam passes through the blue dichroic mirror  54   b  and enters the prism  52   d  through a prism face  52   da  that may be mounted to the other face of the blue dichroic mirror  54   b  via a transparent elastomeric adhesive layer  56   b . The resiliency provided by the adhesive layer  56   b , in turn, aids in positioning the display panel  60 , as further described below. The green incident beam exits another prism face  52   db  of the prism  52   d  to strike the incident face of the display panel  60   c  that is mounted to the prism face  52   db . The display panel  60  modulates the incident green beam before reflecting the modulated green beam along a path similar to the path followed by the incident green beam. The beam splitter  55  directs the modulated green beam through the projection optics  57  to form an image of the modulated green beam on the screen  59 . The three modulated beam images form a color composite image on the screen  59 . 
     For purposes of adjusting the position of one or more of the display panels  60 , as further described below, the prisms  52   b ,  52   c  and  52   d  may be moved by the actuators  62  to reposition the display panels  60  that are attached to the prisms  52 . In some embodiments, for this to occur, the prism  52   a  may be securely mounted to a chassis (not shown) of the light valve  404 , and the other prisms  52   b ,  52   c  and  52   d  may move with respect to the prism  52   a . More particularly, the actuator  62   a  may be mounted between and contact the prism faces  52   ac  and  52   ba . In some embodiments, the actuator  62   a  may also be mounted near the edges of the prism faces  52   cc  and  52   ba . Because the prism  52   a  may be secured to the chassis of the light valve  404  and because the adhesive layer  56   a  provides a resilient bond between the prisms  52   a  and  52   b , the expansion or contraction of the actuator  62   a  causes the display panel  60   a  to rotate in the plane of the diagram. This rotation, in turn, causes the image to translate. In some embodiments, these motions, in turn, may be controlled to locally adjust the modulated red beam image on the screen  59  by adjusting the voltage that is applied to the piezoelectric actuator  62   a , for example. 
     Other actuators  62  may be used to cause both translation and rotation of the other display panels  60  in a similar manner. For example, the actuator  62   b  may be positioned between and contacting the prism faces  52   ab  and  52   ca . In this manner, expansion and contraction of the actuator  62   b  causes rotation and therefore image translation of the display panel  60   b  and thus, may be used to move both the modulated blue and green beam images. 
     Movement of the prism  52   c  by the actuator  62   b  may also cause movement of the prism  52   d  and thus, movement of the display panel  60   c . However, the position of the display panel  60   c  may be adjusted by the actuator  62   c  that may be positioned between and contact the prism faces  52   cb  and  52   da . In this manner, expansion or contraction of the actuator  62   c  may be used to adjust the position of the display panel  60   c  and thus, align the modulated blue beam image with the modulated red and green beam images. 
     Other arrangements are possible. For example, in other embodiments, actuators  62  (not shown) may be used to cause, for example, rotation of a particular display panel  60  about a plane that is orthogonal to the plane of the diagram. 
     The light valve  404  may include a parabolic mirror  65  to collimate rays of light from the light source  63 . The light source  63  may be an arc lamp, for example. The light valve  404  may also include a condensing lens  61  to direct the white beam to the beam splitter  55 . The beam splitter  55 , in turn, may direct the white beam to a polarizer  49  that polarizes the white beam before the beam strikes the prism face  52   aa.    
     The above-described solutions to alignment of the modulated beam images address both pixel translation and rotation. However, rotationally alignment of the modulated beam images may be accomplished in other ways as described below. 
     In general, the effects of rotational misalignment between two modulated beam images  100  and  102  may be very noticeable as depicted in FIG.  11 . As shown, each of the beam images  100  and  102  may have dark lines in between adjacent pixel rows and pixel columns due to the nature of the display panel  60 . Therefore, when the two beam images  100  and  102  are rotated relative to each other, certain parts of the composite image may be partially transparent because the dark lines nearly align with each other in these parts, and other parts of the composite image may be nearly opaque as the dark liner are close together in these parts. Although the beam images  100  and  102  are both translationally misaligned and rotationally misaligned by 1°, the rotational misalignment may be perceptually the most apparent. 
     There are several ways to rotationally align the modulated beam images. For example, the display panels  60  may be securely mounted to the faces of the prisms  52  a during assembly of the system  402 . During the mounting, the convergence targets  425 , for example, may be observed to physically position the display panels  60  correctly to cause beam convergence. 
     Referring to FIG. 13, the projection display  402  may include the electrical system  200  that may be part of a computer system, part of a stand-alone projector, part of a television, or part of a computer monitor as just a few examples. In particular, the electrical system  200  may include a Video Electronics Standards Association (VESA) interface  202  to receive analog signals from a VESA cable  201 . The VESA standard is further described in the Computer Display Timing Specification, v.1, rev. 0.8 that is available on the Internet at www.vesa.orgstandards.html. The analog signals from the cable  201  indicate images to be formed on the display and may be generated by a graphics card of a computer, for example. The analog signals are converted into digital signals by an analog-to-digital (A/D) converter  204 , and the digital signals are stored in a frame buffer  206 . A timing generator  212  may be coupled to the frame buffer  206  and regulate a frame rate at which images are formed on the screen  59 . A processor  220  (one or more microcontroller(s) or microprocessor(s), as examples) may be coupled to the frame buffer  206  via a bus  208 . 
     The processor  220  may process the data stored in the frame buffer  206  to, as examples, transform the coordinate space used by the graphics card into the coordinate space used by the display panels  60 , remap the color space used by the graphics card into the color space used by the display panels  60  and cause the data to conform to the gamma function of the display panels  60 . The end product of these operations is a set of RGB values for each pixel of the image. In this manner, the R values are used to form the intensity values of the pixels of the red display panel  60   a , the G values are used to form the intensity values of the pixels of the green display panel  60   c  and the B values are used to form the intensity values of the pixels of the blue display panel  60   b.    
     As described above, not all of the pixels of a particular display panel  60  may be used. Instead, a map  215  may be stored in a mapping memory  216  that indicates the desired mapping. The map  215 , in turn, may be used by an address generator  214  that generates signals indicative of pixel addresses for pixels of the display panels  60 . Referring to FIG. 14, as an example, for a particular display panel  60 , N locations  252  (locations  252   1 ,  252   2 ,  252   3 , . . .  252   N ) of the map  215  may sequentially indicate the mapping for the uppermost row of a pixel image, beginning with the location ( 0 , 0 ) of the pixel image. As shown, location ( 0 , 0 ) of the pixel image maps into location ( 3 , 3 ) of the display panel  60 , location ( 1 , 0 ) of the pixel image maps into location ( 4 , 3 ) of the display panel  60 , location ( 1 , 1 ) of the pixel image maps into location ( 5 , 3 ) of the display panel  60 , etc. 
     Referring back to FIG. 13, among the other features of the system  200 , the system  200  may include a display panel interface  222  that is coupled to the bus  208  and drives the display panel voltages to form the images on the display panels  60 . A global translation calibration interface  218  (an electromechanical user interface or a serial bus interface, as examples) may be electrically coupled to the address generator  214 . In this manner, the calibration interface  218  may modify the map  215  in response to the global translation indicated by the controls (a computer or a control knob, as examples) that are coupled to the interface  218 . A local translation interface  230  (an electromechanical user interface or a serial bus interface, as examples) may be, for example, coupled to a voltage regulator  231  to selectively control the voltages that are applied to the different piezoelectric actuators  62 . 
     The sensor  414  may be coupled to the processor  220  through the bus  208  and the interface  232 . Thus, the misalignment information detected by the sensor  414  may be analyzed by the processor  220  which then can provide appropriate commands for global or local translation calibrations, in one embodiment of the present invention. 
     While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.