Abstract:
A projection system includes a light source, a display panel and a first circuit. The light source is adapted to generate light, and the display panel includes pixels to modulate at least a portion of the light to produce a modulated beam image. The pixels are formed from groups of subpixel cells, and the display panel is adapted to reorganize the groups to shift positions of the pixels. The first circuit is coupled to the display panel to reorganize the groups.

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 display 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 abeam 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 display 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 ; temporarily mount 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  to test the alignment of the display panels  22 ,  24  and  26 . Referring to FIG. 2, if the LCD display panels  22 ,  24  and  26  are not properly aligned, then the resultant red  40 , green  42  and blue  44  modulated beam images do not align, an alignment problem that may be apparent throughout the entire composite image. However, when the LCD display panels  22 ,  24  and  26  are properly aligned, the modulated beam images align and are not detectable from the composite image, as depicted in FIG.  3 . 
     Unfortunately, aligning the LCD display panels  22 ,  24  and  26  to cause beam convergence may require a high degree of accuracy in the assembly of the system  5 . Furthermore, such factors as aging and thermal drift, may cause the LCD display panels  22 ,  24  and  26  to fall out of alignment during the lifetime of the system  5 . 
     Thus, there is a continuing need to address one or more of the above-stated problems. 
     SUMMARY 
     In one embodiment of the invention, a projection system includes a light source, a display panel and a first circuit. The light source is adapted to generate light, and the display panel includes pixels to, modulate at least a portion of the light to produce a modulated beam image. The pixels are formed from groups of subpixel cells, and the display panel is adapted to reorganize the groups to shift positions of the pixels. The first circuit is coupled to the display panel to selectively cause the display panel to reorganize the groups. 
     In another embodiment, a method includes modulating beams of light with display panels to form a first modulated beam image and a second modulated beam image. The display panel includes display pixels, and the display pixels are associated with image pixels of the first and second modulated beam images. Without moving any of the display panels, the positions of some of the display pixels are changed to move the first modulated beam image with respect to the second modulated beam image. 
     In another embodiment, a method includes generating light and using pixels to modulate at least a portion of the light to produce a modulated beam image. At least two subpixel cells are grouped together to form each display pixel. The grouping of the subpixel cells is changed to shift positions of the display pixels. 
     In yet another embodiment, a display panel includes subpixel cells and a switch circuit. The switch circuit is adapted to form display pixels by grouping the subpixel cells and change the grouping of the subpixel cells to shift positions of the pixels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram of a 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 panels are not aligned. 
     FIG. 3 is an illustration of an image formed by LCD panels of the system of FIG. 1 when the panels are aligned. 
     FIG. 4 is a schematic diagram of a projection system according to an embodiment of the invention. 
     FIG. 5 is an illustration of an alignment scenario between two images projected by display panels of the projection system of FIG.  4 . 
     FIG. 6 is an illustration of the arrangement of subpixel cells of the display panel according to an embodiment of the invention. 
     FIG. 7 is a schematic diagram of circuitry of the display panel according to an embodiment of the invention. 
     FIG. 8 is an illustration of a display panel according to an embodiment of the invention. 
     FIG. 9 is an illustration of portions of two modulated beam images before alignment. 
     FIG. 10 is an illustration of portions of the two modulated beam images after alignment. 
     FIG. 11 is an electrical schematic diagram of the projection system of FIG. 4 according to an embodiment of the invention. 
     FIG. 12 is an illustration of a portion of a pixel map. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 4, an embodiment  50  of a projection system in accordance with the invention has electrical features to cause the convergence of modulated beams images (modulated red, green and blue images, for example) that collectively form a composite image on a screen  59 . In particular, in some embodiments, during calibration, the projection system  50  may use these electrical features to selectively rotate and translate the modulated beam images that are formed by display panels  60  (display panels  60   a ,  60   b  and  60   c , as examples) without physically altering the positions of the display panels  60 . As a result, at the time of manufacture, the display panels  60  may be mounted without a high degree of precision. Furthermore, during the lifetime of the projection system  50 , the positions of the beams may be re-calibrated without remounting or repositioning the display panels  60 . In some embodiments, the projection system  50  may be a liquid crystal display (LCD) projection system, and the display panels  60  may be reflective LCD display panels. Other arrangements are possible. 
     More particularly, FIG. 5 illustrates two modulated beam images  63  (represented by solid lines) and  65  (represented by dashed lines), each of which is formed by a different display panel  60 . Each pixel  67  of the beam image  63  is located 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 cartesian coordinate location (0,0) of the image  65  is 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, the projection system  50  may generate internal signals (described below) that may be applied to one or both of the display panels  60  that generate the images  63  and  65  to cause the display panel(s)  60  to shift the modulated beam image(s) to adjust beam convergence. 
     Each pixel  67  of a modulated beam image may be formed from a corresponding pixel  46  (see FIG. 6, described below) of a display panel  60 , and the position of the pixel  46  may be shifted by ½ pixel (for example) in response to the internal signals. As an example, FIG. 6 depicts a portion  61  of a display panel  60  and illustrates that, in some embodiments, each pixel  46  of the display panel  60  may be formed from a group (a group of two, for example) of subpixel cells  48 . In this manner, the display panel  60  may be controlled via the internal signals to selectively group the subpixel cells  48  to form the pixels  46 , a flexibility that permits shifting of the positions of the pixels  46 , as described below. 
     In some embodiments, the subpixel cells  48  may be arranged in a rectangular array of rows and columns, and each pixel  46  may be formed from two adjacent subpixel cells  48  of the same column. Thus, as depicted in FIG. 6, a particular pixel  46   a  may be formed from subpixel cells  48   a  and  48   b , each of which forms ½ of the pixel  46 . In response to the assertion of a signal (called SPLIT, described below), all pixels  46  that are in the same column as the pixel  46   a  may be effectively shifted in a downward direction by ½ pixel. In this manner, the assertion of the SPLIT signal causes the subpixel cells  48  of the column to reorganize, or regroup, so that the pixel  46   a  becomes the pixel  46   a ′. The pixel  46   a ′ includes the subpixel cells  48   b  and  48   c  and does not include the subpixel cell  48   a.    
     Many other embodiments are possible. For example, in response to the assertion of the SPLIT signal, a column of pixels  46  may be shifted in an upper direction by ½ pixel, or a row of pixels  46  may be shifted to the right by ½ pixel or shifted to the left by ½ pixel. Also, more than two subpixel cells  48  may form each pixel  46 . Furthermore, in some embodiments, the shifts may cause less or more than a ½ pixel shift. For example, in other embodiments, each pixel  46  may be formed by four subpixel cells  48 , and as a result, each pixel  46  may be shifted by ¼ pixel in response to the assertion of the SPLIT signal. In some embodiments, the number of subpixel cells  48  that are used to form each pixel  46  may be limited by an inter-pixel gap  42 , a minimum spacing to ensure the subpixel cells  48  do not short out. 
     As described below, the shifting of a particular column of pixels  46  may be controlled by an associated SPLIT signal, where the notation denotes the coordinate position of the column. As an example, in some embodiments, when the SPLIT 100  signal is asserted (driven high, for example), the pixels  46  of column  100  may be shifted in a downward direction by approximately ½ pixel. 
     The above-described techniques may be used to adjust for fine, or local, adjustment of the pixel positions i.e., an adjustment that is approximately less than one pixel in a particular direction. However, more coarse, or global, adjustments may be desired, i.e., adjustments greater than about one pixel may be desired. In some embodiments, these global adjustments may be performed by remapping pixel positions, as described below. For example, two modulated beams may be rotated with respect to each other, as depicted in FIG. 9, by a row  62  of pixels of a modulated beam image being rotated with respect to a row  64  of pixels of another modulated beam image. To cause the modulated beam images to converge, the columns of one of the beam images may be subdivided into segments, and these segments may be selectively shifted (as described above) and remapped (as described below) to cause beam convergence. 
     For example, referring to FIG. 10, using the rows  62  and  64  to illustrate the rotation, the row  62  may be conceptually divided into segments  66  (segments  66   a ,  66   b  and  66   c , as examples) that are selectively shifted down and remapped to substantially align the rows  62  and  64 . In this manner, the shifting and apparent rotation of the row  62  is performed by the shifting and rotation of the pixels  46  of the display panel  60  that form the row  62 . Although each segment  66  of the row  62  may have the same slope both before and after alignment, local and global shifting of the segments  66  in the vertical direction may be used to substantially aligns the two rows  62  and  64 , as described below. 
     The local realignment of a particular segment  66  may be accomplished by shifting the pixels  46  that form the segment  66  in a downward direction by ½ pixel using the technique of selectively regrouping subpixel cells  48 , described above. The global realignment of the segment  66  may be accomplished by remapping the coordinates of the pixels  46  that form the segment  66 . For this to occur, the display panel  60  may include extra subpixel cells  48  in addition to the number of subpixel cells that are used to furnish the desired image resolution. 
     Referring to FIG. 8, as an example, the display panel  60  may include a block  75  of active pixels (that are currently being used to form an image) and inactive pixels  77  (i.e., that are turned off pixels) that may become part of the active block  75  due to remapping. Thus, the block  75  of active pixels  46  is driven by electrical signals that represent a pixel image and the needed modulation. To define which pixels  46  form the active block  75 , the projection system  50  may apply a mapping transformation to transform coordinates of an image space in which the pixel image is defined to coordinates that identify the active block  75 . The mapping transformation, in turn, may globally reposition the modulated beam image that is formed by the display panel  60 . 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 each direction. 
     Referring back to FIG. 10, as an example, the above-described techniques may be applied to substantially align the rows  62  and  64 . For this example, each pixel  46  is assumed to be formed from two subpixel cells  48 , and the alignment error may be kept under ¼ pixel, as described below. In particular, the pixels  46  that form the segment  66   a  of the row  62  may be shifted down by ½ pixel by asserting the appropriate SPLIT signals. This shift causes the leftmost pixel of the segment  66   a  to be shifted down by ¼ of a pixel from the corresponding pixel of the row  64  and causes the rightmost pixel  46  of the segment  66   a  to be located ¼ pixel above the corresponding pixel  46  of the row  64 . The next segment  66   b  of the row  62  is apparently rotated by remapping the pixels  46  that form the segment  66   b  down by one pixel  46  and by not shifting the pixels  46  of the segment  66   b . As a result, the leftmost pixel of the segment  66   c  is located ¼ of a pixel down from the corresponding pixel of the row  64 , and the rightmost pixel of the segment  66   c  is located ¼ of a pixel up from the corresponding pixel of the row  64 . The next segment  66   c  is formed by asserting the appropriate SPLIT signals for the corresponding pixels  46  and by remapping the corresponding pixels  46  down by one row. The next segment  66   d  is formed by remapping the pixels down by two pixels and not shifting the pixels. 
     Thus, to summarize the rotation techniques used in this example, the above-described sequence may be repeated to effectively rotate the row  62 : every two segments  66 , the corresponding pixels  46  are remapped down one additional pixel, and the SPLIT signals are asserted for every other segment to shift the positions of the pixels  46  of the segment  66  by ½ pixel. 
     Referring back to FIG. 4, in some embodiments, the projection system  50  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 adhesive layer. 
     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 adhesive layer. 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 the 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 . 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 adhesive layer. 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   c  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 . 
     The projection system  50  depicted in FIG. 4 is an example of one of many possible embodiments of the invention. Other projection systems, prism arrangements and optical systems are possible. 
     Referring to FIG. 7, the display panel  60  may include the following circuitry, a portion of which is depicted in FIG.  7 . In particular, the display panel  60  may include row lines  71 , column lines  73  and split lines  77  (each receiving a different SPLIT signal) to selectively activate the pixels  46  and selectively group the subpixel cells  48  to form the pixels  46 . In this manner, each pixel  46  may be uniquely addressed by the assertion of one of the row lines  71  and one of the column lines  73 . As an example, the split line  77  and the column line  73  shown in FIG. 7 receive SPLIT N  and COL N  signals, respectively; one of the row lines  71  shown in FIG. 7 receives a ROW M  signal; and the other row line  71  receives a ROW M+1  signal. 
     The split lines  77 , in turn, control the grouping of the subpixel cells  48 . More particularly, the optical output signal of each subpixel cell  48  may be controlled via an associated electrode plate  54  (plates  54   a ,  54   b ,  54   c  and  54   d , as examples), and electrode plates  54  of the same pixel  46  are electrically coupled together to group form the subpixel cells  48  for that pixel  46 . The grouping of the subpixel cells  48  is controlled by switch circuits  49  (switch circuits  49   M  and  49   M+1 , as examples), each of which is associated with three electrode plates  54 . Except for the plates  54  that are associated with the subpixel cells  48  at the edge of the display panel  60 , each electrode plate  54  is associated in common with two switch circuits  49 , an association that permits the shifting, as described below. 
     As an example, the switch circuit  49   M  is associated with three electrode plates  54   a ,  54   b  and  54   c ; and the switch circuit  49   M+1  is associated with the electrode plate  54   c , the electrode plate  54   d  and another electrode plate (not shown). Thus, the switch circuits  49   M  and  49   M+1  are both associated with the electrode plate  54   b . In this manner, when the SPLIT N  signal is deasserted (driven low, for example), the switch circuit  49   M  directs a voltage from the associated row line  71  to the electrode plates  54   a  and  54   b  to activate the subpixel cells  48  that are coupled to the electrode plates  54   a  and  54   b . However, when the SPLIT N  signal is asserted (driven high, for example), the switch circuit  49   M  directs the voltage from the associated row line  71  to the electrode plates  54   b  and  54   c , an action that shifts the associated pixel  46  by ½ pixel. 
     In some embodiments, the switch circuit  49   a  may include an n-channel metal-oxide-semiconductor (nMOS) field effect transistor  59  that has its drain-source path coupled between the electrode plates  54   a  and  54   b , and its gate coupled to a signal called SPLIT N # that is the inverse of the SPLIT N  signal. The electrode plate  54   b  is coupled to a capacitor  52  that stores a charge indicative of a voltage that is supplied by the row line  71  when the column line  73  is asserted. The coupling of the row line  71  to the capacitor  52  occurs due to an nMOS transistor  50  that has its drain-source path coupled between the row line  71  and the capacitor  52 . The gate of the transistor  50  is coupled to the column line  73  to selectively cause the transistor  50  to conduct. The electrode plate  54   b  may be selectively coupled to the plate  54   c  via the drain-source path of a nMOS transistor  60 . The gate of the transistor  60  is coupled to the split line  75  and thus, is selectively activated by the SPLIT signal. The other switch circuits  49  may have a design similar to the switch circuit  49   M . 
     Referring to FIG. 11, the projection system  50  may include the following electrical system  200  that may be part of a computer system, for example, or part of a stand-alone projector. 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.org/standards.html. These analog signals indicate images to be formed on the display  59  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 central processing units (CPUs), microcontrollers or microprocessors, 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 may be used to form the intensity values of the pixels of the display panel  60   a , the G values may be used to form the intensity values of the pixels of the display panel  60   c  and the B values may be used to form the intensity values of the pixels of the 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 transformation. The map  215 , in turn, may be used by an address generator  214  that generates the pixel addresses for pixels of the display panels  60 . Referring to FIG. 12, as an example, for a particular display panel  60 , P locations  252  (locations  252   1 ,  252   2 ,  252   3 , . . .  252   P ) of the map  215  may sequentially indicate the mapping for the uppermost row  300  of a pixel image, for example, beginning with a pixel  302   0  of the row  300  that is at location (0,0). As shown, the pixel  302   0  at location (0,0) maps into the pixel  46  at location (3,3) of the display panel  60 ; the pixel  302   1  at location (1,0) maps into the pixel  46  at location (4,3) of the display panel  60 ; the pixel  302   2  at location (2,0) maps into the pixel  46  at location (5,3) of the display panel  60 ; etc. 
     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  in response to signals that are furnished by the frame buffer  206  and the address generator  214 . A 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 desired calibration that is indicated by the interface  218  in the following manner. In particular the address generator  214  may include a split register  217  that may indicate, for example, the number of pixel columns that are in each split/unsplit group of pixels  46 . For the example depicted in FIG. 10, each split/unsplit group includes two segments  66 , i.e., twenty-four pixel columns. The address generator  214  may also include an offset register  219  to indicate how many pixel columns are in each mapping. For the example depicted in FIG. 10, twenty-four pixel columns are in each mapping. Thus, if no rotation is needed, the offset register  219  may indicate the total number of pixel columns. The address generator  214  furnishes the SPLIT signals and modifies the map  215  in accordance with the values stored in the offset  219  and split  217  registers. 
     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.