Patent Abstract:
A system and method for displaying an image are provided. In one embodiment, the method includes receiving a data stream representing a frame of an image. The data stream may indicate a first color pixel cluster corresponding to a first color and a second color pixel cluster corresponding to a second color. The first color pixel cluster and the second color pixel cluster may be displayed. The first color pixel cluster may be different from the second color pixel cluster.

Full Description:
This application is a division of application Ser. No. 12/236,379, filed Sep. 23, 2008 (now U.S. Pat. No. 8,237,731), the entirety of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     This relates generally to display systems and, more particularly, to display systems employing data reduction by grouping pixels. 
     Spatial light modulators are devices that may be used in a variety of optical communication and/or video display systems. In some applications, spatial light modulators may generate an image by controlling a plurality of individual elements that control light to form the various pixels of the image. One example of a spatial light modulator is a digital micromirror device (“DMD”), sometimes known as a deformable micromirror device. At least some spatial light modulators are illuminated completely in one color at a time. For example, a spatial light modulator may first be illuminated in red light and then it may be illuminated in green light. Because each color is done individually, the more time that is devoted to a particular color or to an additional color necessarily reduces the time available for display of the remaining colors. For example, in a three-color system the spatial light modulator may only be illuminated in red light less than one-third of the time. 
     Each pixel of light on the screen is a combination of different colors (e.g., red, green and blue). To display the image, the spatial light modulator relies on the user&#39;s eyes to blend the different colored lights into the desired colors of the image. For example, an element of the spatial light modulator responsible for creating a purple pixel will only reflect the red and blue light to the display surface. The pixel itself is a rapidly, alternating flash of the blue and red light. A person&#39;s eyes will blend these flashes in order to see the intended hue of the projected image. 
     Data received from a video source may control operation of a spatial light modulator. Processing this data may require considerable bandwidth and storage capacity. 
     SUMMARY 
     A system and method for displaying an image are provided. In one embodiment, the method includes receiving a data stream representing a frame of an image. The data stream may indicate a first color pixel cluster corresponding to a first color and a second color pixel cluster corresponding to a second color. The first color pixel cluster and the second color pixel cluster may be displayed. The first color pixel cluster may be different from the second color pixel cluster. 
     Technical advantages of some embodiments of the present disclosure may include the ability to reduce the amount of data processed by an image data processing system without significantly reducing image quality by grouping pixels. By reducing data according to the teaching of the present invention, some electronic components that drive a modulator may be eliminated or their capacity may be reduced. For example, an image data processing system may require less expensive or fewer memory chips. It may also consume less power and operate with less frame buffer storage capacity. 
     Other technical advantages of the present disclosure may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and for further features and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of one embodiment of a portion of a video display system implementing pixel grouping, in accordance with particular embodiments; 
         FIG. 2  is a block diagram of an image data processing system, in accordance with particular embodiments; 
         FIG. 3A  illustrates a single pixel cluster, in accordance with particular embodiments; 
         FIG. 3B  illustrates a double pixel cluster, in accordance with particular embodiments; 
         FIG. 3C  illustrates a quad pixel cluster, in accordance with particular embodiments; 
         FIG. 3D  illustrates double and triple pixel clusters; and 
         FIG. 4  illustrates a sequence for mapping clusters of image data in separate subframes, in accordance with particular embodiments. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a block diagram of one embodiment of a portion of a video display system implementing a pixel grouping display of an image. In this example, video display system  10  includes three light sources  12 , optics  14 , modulator  16  and display surface  18 . In example embodiments, these components may work together to display an image having a particular pixel pattern including grouped or clustered pixels on display surface  18 , as described in greater detail below with respect to  FIGS. 2-4 . Light beams  20  from any of three light sources  12  pass through optics  14  and emerge as projected beam  22 . Projected beam  22  may be projected toward modulator  16 . 
     Modulator  16  may then direct a portion of projected beam  22  towards a light dump along off-state light path  24  and/or a portion of projected beam  22  towards display surface  18  along on-state light path  26 . In certain embodiments, modulator  16  may be illuminated by only one light source  12  at a time. 
     Light sources  12  may comprise any of a variety of different types of light sources, such as, for example, a metal halide lamp, a xenon arc lamp, an LED, a laser, etc. Each light source  12  may be capable of generating a respective light beam  20 . Each light beam  20  may be of a different color (e.g., red, green, blue, yellow, cyan, magenta, white, etc.) or one or more colors may be repeated (e.g., there may be two red beams, one blue beam and one green beam). For example, in  FIG. 1  light source  12   a  may be a red laser, light source  12   b  may be a green laser, and light source  12   c  may be a blue laser. While only three light sources  12  have been depicted, other embodiments may include additional light sources and/or additional colors. The additional colors may, for example, be used to create certain effects or to manipulate the color space. 
     Optics  14  may comprise a lens and/or any other suitable device, component, material or technique for bending, reflecting, refracting, combining, focusing or otherwise manipulating light beams  20  to produce projected beam  22 . An active area may be a portion of modulator  16  that maps to the visible area of display surface  18  driven by modulator  16  (e.g., light incident on the active area may be directed along on-state light path  26  towards display surface  18 ). It may be appreciated that video display system  10  may also include additional optical components (not explicitly shown), such as, for example, lenses, mirrors and/or prisms operable to perform various functions, such as, for example, filtering, directing, reimaging, and focusing beams. For example, some embodiments may use separate optics for each light source  12 . 
     Modulator  16  may comprise any device capable of selectively communicating, for example by selective redirection, at least some of the light from projected beam  22  along on-state light path  26  and/or along off-state light path  24 . In various embodiments, modulator  16  may comprise a spatial light modulator, such as, for example, a liquid crystal display (LCD) modulator, a reflective liquid crystal on silicon (LCOS) modulator, an interferometric modulator, or a microelectromechanical system (MEMS) modulator. In particular embodiments, modulator  16  may comprise a digital micromirror device (DMD). 
     The DMD may be a MEMS device comprising an array of tilting micromirrors. The number of micromirrors may correspond to the number of pixels of display surface  18 . From a flat state, the micromirrors may be tilted, for example, to a positive or negative angle to alternate the micromirrors between an “ON” state and an “OFF” state. In particular embodiments, the micromirrors may tilt from +10 degrees to −10 degrees. In other embodiments, the micromirrors may tilt from +12 degrees to −12 degrees, or from +14 degrees to −14 degrees. 
     To permit the micromirrors to tilt, each micromirror may be attached to one or more hinges mounted on support posts and spaced by means of an air gap over underlying control circuitry. The control circuitry may provide electrostatic forces based, at least in part, on image data received from an image source (e.g., a Blu-ray disc™ player or cable box). The electrostatic forces may cause each micromirror to selectively tilt. Incident light illuminating the micromirror array may be reflected by the “ON” micromirrors along ON-state light path  26  for receipt by display surface  18  or it may be reflected by the “OFF” micromirrors along OFF-state light path  24  for receipt by a light dump. The pattern of “ON” and “OFF” mirrors (e.g., light and dark mirrors) forms an image that may be projected onto a display screen  18 . 
     Display surface  18  may be any type of screen able to display a projected image. For example, in some embodiments display surface  18  may be part of a rear projection TV. In particular embodiments, display surface  18  may be a screen used with a projector, or even simply a wall (e.g., a wall painted with an appropriate color or type of paint). 
     In an alternate embodiment, video display system  10  may comprise a single light source  12 . Light source  12  may be projected through a color wheel that may sequentially filter the light of light source  12  into two or more colors. The color wheel may include colors red, green, and blue. It may work in conjunction with the light beam  20  to alternatively direct two or more different colors of light beam  20  toward modulator  16  at predetermined time intervals. Given these predetermined time intervals, modulator  16  may then proportionately mix each of the colors in order to produce many of the other colors within the visible light spectrum. 
     In another alternate embodiment, modulator  16  may be the final display surface viewed by the user, for example in a viewfinder display application. 
       FIG. 2  illustrates an image data processing system  40  in accordance with an embodiment. Image data processing system  40  may include formatter  52 , buffer  54 , and modulator  16 . Image data processing system  40  may receive image data from a video source and process it such that micromirrors on modulator  16  display an image corresponding to the video source data. 
     Modulator  16  may operate by a pulse width modulation (PWM) scheme. Generally, the incoming video image data signal is digitized into samples using a predetermined number of bits for each element. The predetermined number of bits is often referred to as the bit depth, particularly in systems employing binary bit weights. Generally, the greater the bit depth, the greater the number of colors (or shades of gray) modulator  16  can display. 
     Image data  42  may be received from a video source. Image data  42  may include multiple bit groups  42   1 - 42   n . Each bit group  42   1 - 42   n  may be used by image data processing system  40  to control micromirrors of modulator  16  to allow modulator  16  to display a frame of an image. Each bit group  42   1 - 42   n  may correspond to a single micromirror of the array of micromirrors of modulator  16 . Thus, bit group  42   1  may provide information to modulator  16  to direct the control of a single micromirror for a single color during a single frame of image data. In one embodiment, the color may be green. Thus, bit group  42   1  may control a single micromirror of modulator  16  that will direct the illumination of green light on a single pixel of display  18  during a single frame. 
     Bit groups  42   1 - 42   n  may each be comprised of a series of bits  44 . For example, bit group  42   1  may include eight bits  44 , making a byte. In alternative embodiments, each of bit groups  42   1 - 42   n  may include fewer than eight bits or more than eight bits. For example, bit groups  42   1 - 42   n  may include six or four bits. Four bits may be sufficient to display text. Each bit  44  may have a corresponding bit plane value  46  associated with it. The higher the bit plane value  46 , the greater the amount of time a pixel associated with that bit is illuminated with a particular color during the frame. More significant bits  48  may be displayed a longer amount of time during the frame (e.g., may set a micromirror to an “ON” state for a longer amount of time), while less significant bits  50  may be displayed a shorter amount of time during the frame. In particular embodiments, more significant bits may correspond to those bits with a bit plane value of seven or eight, and less significant bits  50  may correspond to bits with bit plane values of six or less. 
     Formatter  52  may receive image data  42  and translate it into commands that can be understood by modulator  16 . Formatter  52  may be any suitable processing device, for example, an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). In accordance with embodiments, formatter  52  may process image data  42  such that the amount of data flowing through image data processing system  40  to modulator  16  may be reduced. This reduction of data flow may allow the bandwidth of associated data buses to be reduced and may also allow buffer  54  to operate with less random access memory (RAM). In accordance with an embodiment, image data processing system  40  may operate with fewer or slower or lower cost memory chips due to the ability to process less data to display an image. In addition, the size or speed or cost of the formatter circuitry can be reduced. This reduction in data may be accomplished while continuing to maintain the quality of an image. 
     With conventional image display systems, image data  42  may be processed such that all of the bits  44   1  of a single bit group  42   1  are used to control only a single one of the micromirrors of modulator  16 . In accordance with particular embodiments, image data  42  may be modified such that groups or clusters of more than one micromirror of modulator  16  and the display of corresponding pixels are controlled by the same bits  44   1  of a single bit group  42   1 . Pixels, micromirrors and other similar devices, such as a portion of a liquid crystal cell, are herein referred to generally as pixel elements. Thus, by processing image data  42  to allow multiple micromirrors to be controlled by data that would normally control a single micromirror, data flow through image processing system  40  may be reduced. For example, the same amount of data that would be necessary to control one row of micromirrors/pixels may be used to control two adjacent rows of micromirrors/pixels. In this manner, data flow through image processing system  40  may be reduced to half. 
     As discussed below in conjunction with  FIGS. 3A-3C  and  4 , this grouping of pixels may be accomplished in various ways. In one example, clustering is performed according to data corresponding to certain ones of the primary colors used to generate the color of the pixel during a given frame (e.g., red, green, and blue). Reduction of data usage may also be accomplished by loading bits having lower bit plane values in clusters. However, bits  44  with higher bit plane values should be loaded for each distinct pixel element because the effect of a change in their value is much more significant than those with lower bit plane values  46 . By loading bits in this manner, bits  44  associated with lower bit plane values may control a corresponding group of micromirrors/pixels. In addition, pixel clusters may be displayed in a first subframe of an image frame. A second pixel cluster corresponding to the same image as the first pixel cluster may be displayed in a second subframe. This display in the second subframe may be offset from the display in the first subframe to create an on-chip smoothing, as discussed in greater detail below. 
       FIGS. 3A ,  3 B, and  3 C, each illustrates different pixel clusters which make up pixel patterns in accordance with embodiments. As used herein, one or more than one pixel may make up a pixel cluster.  FIG. 3A  illustrates display  65 . Display  65  includes pixel array  60 . Pixel array  60  may include M columns by N rows of pixels. Modulator  16  shown in  FIGS. 1 and 2  may include an array of micromirrors corresponding to pixel array  60 .  FIG. 3A  illustrates a single pixel cluster  64 . 
     Image data may be received by image data processing system  40  for display on display  65 . Image data  42  may correspond to a frame of a frame sequential color image or video sequence. Image data  42  may also direct the display of certain colors of the image. For example, image data  42  may direct the display of different shades (lightness quantities) and/or different combinations of each of the colors green, red, and blue. In accordance with embodiments, pixels  62  may be grouped into particular pixel clusters depending upon the color that image data  42  represents. For example, image data  42  that represents the color green may be loaded to image data processing system  40  in accordance with a 1×1 single pixel cluster and corresponding display resolution resulting in single pixel cluster  64 . That is, when display  65  displays a green portion of an image, it may have an image resolution made up of an array of 1×1 pixel clusters  64  forming a single pixel pattern across display  65 . This corresponds to a conventional approach. 
     Data reduction may be achieved in connection with display  65  showing red or blue portions, for example, of an image frame. Thus, when image data  42  is loaded into image data processing system  40  that corresponds to the colors red or blue, the pixels may be grouped into double pixel clusters  68   a , a group of which may form double pixel pattern  66  as shown in  FIG. 3B . Accordingly, image data  42  needed to display red and blue on display  65  may be reduced to half. By maintaining the green image data as a single pixel pattern and allowing the red and blue data to be displayed in a double pixel pattern, data processed by image data processing system  40  may be reduced while maintaining image quality. This particular pixel pattern  66  in  FIG. 3B  is offset, as described in greater detail below. 
     Other embodiments may allow red data to be reduced by half, resulting in a double pixel pattern  66 , while blue data is reduced four times, resulting in quad pixel pattern  70  shown in  FIG. 3C . That is, in certain embodiments, a single image frame may display green data as a single pixel pattern with an array of 1×1 pixel clusters. The same image frame may display red data in a double pixel pattern  66  with 1×2 pixel clusters  68   a , and in the same image frame, blue data may be displayed in quad pixel pattern  70  resulting in 2×2 quad pixel clusters  72 . 
       FIG. 3D  illustrates other pixel clusters in accordance with embodiments. Double pixel cluster  68   b  may be similar to double pixel cluster  68   a  but oriented in a horizontal direction. Triple pixel clusters  69   a  and  69   b  are clusters of three adjacent pixels and may be configured in the orientations shown. 
     The groupings of the pixel clusters may be offset as double pixel pattern  66  as shown in  FIG. 3B . This offset may allow the image to be displayed without visible lines running horizontally through the image that may otherwise result if the grouping is merely done by grouping rows 1 and 2 as a first group and rows 3 and 4 as a second group. This grouping without an offset may result in a line visible on the image between rows 2 and 3. Offsetting, such that a first pixel cluster  68   a  corresponds to column 1, pixels 2 and 3 and a second pixel cluster  68   a  corresponds to column 2, rows 1 and 2, may avoid unwanted horizontal lines through an image. The offset may be a single pixel as shown. 
     Colors may be selected for data reduction based on the luminance and/or the amount of time the color is to be displayed per frame. For example, a green LED may be the least efficient so it may need to be left on the longest. Red may be more efficient than green, and blue may be more efficient than red. Green, red, then blue may also be the order of luminance or perceived brightness of the colors. When loading the pulse width modulation data, due to the luminance and the amount of time the color needs to remain ON during the frame, it may be possible to load more bits in green than red, and more bits in red than blue. Accordingly, data reduction in accordance with an embodiment of the present disclosure may include a single pixel pattern may correspond to green, a double pixel pattern may correspond to red, and a quad pixel pattern may correspond to blue. However, other patterns and other colors may be used. 
     As is well known with display systems employing frame sequential color, during a single image frame the display of the colors may be divided into percentages of time the color is illuminated on display  65  to effect the appearance of a chosen color for that pixel for that frame, such as purple. For example, green may use approximately 50% of the time of the frame, red may use approximately 30% of the time of the frame, and blue may use approximately 20% of the time of the frame. Because green may be on for half of the frame time, there may be more time to load more data. This may correspond to the ability to load data corresponding to each pixel for green and being able to reduce the amount of data by grouping the pixels for red and blue. The teachings of the present invention could be used with more than just green, red and blue colors. For example, other color fields may be narrowband colors (e.g., orange) or combinations of single colors such as, for example, cyan which is a combination of green and blue. 
     After the image data  42  is processed to allow data reduction, it may be stored in buffer  54  before it is transmitted to modulator  16 . Because the data is reduced before it is stored in buffer  54 , buffer  54  may be allowed to have less capacity, and thus be cheaper, resulting in an overall less expensive image display system  40 . 
     In accordance with another embodiment, overlapping images of the same color may be loaded with different pixel groupings based on bit plane value  46 . For example, less significant bits  50  may be loaded in groups, while more significant bits  48  may be loaded one at a time. This may result in a 1×1 pixel cluster for more significant bits, which may correspond to bit plane values  46  of 7 and 8, in one example. Data in bit planes 7 and 8 may correspond to progressively longer duration pixel state settings. In a binary weighting scheme, each bit plane may correspond to approximately twice the time of the next shorter bitplane, but other weightings are frequently used. Bit plane values  46  of six or less may be less significant bits, and may be loaded in groups of four bits as depicted in  FIG. 3C  showing quad pixel cluster  72 . 
     When grouping is done by bit plane in accordance with an embodiment, bits with bit plane values of 7 and 8 may control a single micromirror of modulator  16  and corresponding pixel  62 , while less significant bits corresponding to bit plane values of 1 through 6 may control a group of micromirrors corresponding to pixel clusters  68   a  and  72 . These groupings may be double pixel cluster  68   a  as shown in  FIG. 3B  or quad pixel cluster  72  as shown in  FIG. 3C . More significant bits may correspond to a single pixel because the loading time of the more significant bits is higher than the load time for the less significant bits. 
     The data reduction techniques described herein may be combined with more conventional data reduction techniques, such as reducing bits per pixel. For example, data reduction techniques described herein may be combined with the data corresponding to six bits or four bits per pixel resulting in even more data reduction. Moreover, pixel grouping is not limited to double or quad pixel grouping, but rather any suitable number of pixels may be grouped. For example, certain embodiments may employ data reduction by grouping three pixels. 
       FIG. 4  illustrates a sequence  78  that may be followed to produce on-chip smoothing of the display, such as SmoothPicture™ technology used with Texas Instruments products, using pixel groupings in accordance with embodiments of the present disclosure. Conventional smoothing technology, which employs an optical actuator to display two or more pixel fields sequentially with different offsets to increase effective image resolution, is well known in the art. 
     Display  84  may be comprised of pixel array  90 . Pixel array  90  may include M columns and N rows of pixels  92 . In order to create a virtual smoothing effect, a first pixel cluster or superpixel  86  may comprise four pixels that are grouped and controlled with corresponding image data in accordance with embodiments. A first superpixel  86  may be displayed in a first subframe  80  of a corresponding image frame. The image frame may comprise first subframe  80  and second subframe  82 . At a subsequent point in time, a second superpixel  88  corresponding to the same image of first superpixel  86  may be displayed in second subframe  82 . The display of second superpixel  88  may be offset a full pixel from the display of first superpixel  86 . This sequential display of a second superpixel  88  offset from a first superpixel may create a virtual smoothing effect. In accordance with an embodiment, a similar result may be accomplished merely by loading a second superpixel  88  offset in a second subframe  82  offset from a first superpixel  86  in a first subframe  80 . A pixel array  90  of on-chip smoothing sequence  78  may be a diagonal (sometimes referred to as a diamond) array as illustrated in  FIG. 4 . In an alternate embodiment, pixel array  90  may be an orthogonal array as illustrated in  FIGS. 3A-3C . 
     It should be understood that various modifications may be made to the described embodiments without departing from the spirit and scope of the invention as defined by the appended claims.

Technology Classification (CPC): 6