Abstract:
The disclosed embodiments relate to a system and method for compensating for spoke light in a video unit ( 10 ). More specifically, there is provided a method comprising measuring a first light level during a non-spoke time of a color wheel ( 14 ) to generate a non-spoke light level; and setting a spoke light compensation value based on the measured non-spoke light level. There is also provided a video unit ( 10 ) comprising a light source ( 12 ) configured to generate a first light level during a non-spoke time of a color wheel ( 14 ), a photodiode assembly ( 26 ) configured to measure the first light level to generate a non-spoke light level, and a processor ( 20 ) configured to set a spoke light compensation value based on the non-spoke light level.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to projecting video images onto a screen. More specifically, the present invention relates to a spoke light recovery techniques in a video projection unit.  
       BACKGROUND OF THE INVENTION  
       [0002]     This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.  
         [0003]     Digital Light Processing (“DLP”) is a display technology that employs an optical semiconductor, known as a Digital Micromirror Device (“DMD”) to project video onto a screen. DMDs typically contain an array of at least one million or more microscopic mirrors mounted on microscopic hinges. Each of these mirrors is associated with a point on the screen, known as a pixel. By varying the amount of light that is reflected off each of these mirrors, it is possible to project video onto the screen. Specifically, by electrically actuating each of these hinge-mounted microscopic mirrors, it is possible to either illuminate a point on the screen (i.e., “turn on” a particular micromirror) or to leave that particular point dark by reflecting the light somewhere else besides the screen (i.e., “turn off” the micromirror). Further, by varying the amount of time a particular micromirror is turned on, it is possible to create a variety of gray shades. For example, if a micromirror is turned on for longer than it is turned off, the pixel that is associated with that particular micromirror will have a light gray color; whereas if a particular micromirror is turned off more frequently than it is turned on, that particular pixel will have a darker gray color. In this manner, video can be created by turning each micromirror on or off several thousand times per second. Moreover, by sequentially shining red, green, and blue at the micromirrors instead of white light, it is possible to generate millions of shades or color instead of shades of gray.  
         [0004]     As stated above, the shading of a particular pixel may be partially determined by the length of time that the micromirror corresponding to that pixel is either turned on or turned off. This shading can be quantified using a measurement referred to as the least significant bit (“LSB”). For example, DMDs are typically configured to display  256  shades from off (0 LSBs) to all on (256 LSBs) with each shade between 0 and 255 becoming successively brighter. It is possible to create a variety of different color shades by combining various LSBs of red light, green light, and blue light (i.e., primary colors of light). For example, one color shade may be formed from 30 LSBs of red light, 150 LSBs of green light, and 85 LSBs of blue light, another shade from 212 LSBs of red light, 156 LSBs of green light, and 194 LSBs of blue light, and so forth. Because the three colors of light are shined sequentially and rapidly, a viewer sees a single shade of light formed from the three different colors of light.  
         [0005]     One technique for generating the sequential stream of colored light is with a color wheel. A color wheel typically includes six color filters arrayed red, green, blue, red, green, blue around the circumference of a wheel. By shining white light at the circumference of the color wheel and rotating the color wheel, it is possible to generate a sequential stream of red, green, and blue light. However, the colored light may become briefly inconsistent when the colored light transitions between primary colors. Due to this variance in color, the light generated during these transitions, which are referred to as spoke times may not be employed.  
         [0006]     In certain circumstances, however, a technique known as spoke light recovery (“SLR”) maybe employ to use light generated during spoke times. In particular, if the shade of the red light, green light, and blue light components of a pixel are each above a threshold LSB value (e.g., 150) the light generated during the spoke times can be employed. Although SLR can boost the light output for certain shades of light, this boost in light output can create a sudden increase in light output when a video display switches from a non-SLR shade to an SLR shade. Conventional SLR systems compensate for this boost in light output decreasing the non-spoke light by a fixed amount when SLR is employed. However, as light sources age, the amount of light that the light source generates may change, and a fixed compensation cannot adjust for these changes.  
         [0007]     An improved method and system for spoke light compensation is desirable.  
       SUMMARY OF THE INVENTION  
       [0008]     Certain aspects commensurate in scope with the disclosed embodiments are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.  
         [0009]     The disclosed embodiments relate to a system and method for compensating for spoke light in a video unit. More specifically, there is provided a method comprising measuring a first light level during a non-spoke time of a color wheel to generate a non-spoke light level; and setting a spoke light compensation value based on the measured non-spoke light level. There is also provided a video unit comprising a light source configured to generate a first light level during a non-spoke time of a color wheel, a photodiode assembly configured to measure the first light level to generate a non-spoke light level, and a processor configured to set a spoke light compensation value based on the non-spoke light level. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Advantages of the invention may become apparent upon reading the following detailed description and upon reference to the drawings in which:  
         [0011]      FIG. 1  is a block diagram of a video unit configured to calculate a spoke light compensation value in accordance with embodiments of the present invention;  
         [0012]      FIG. 2  is a diagram of a color wheel in accordance with embodiments of the present invention;  
         [0013]      FIG. 3  is a diagram of photodiode assembly configured to calculate a spoke light compensation in accordance with embodiments of the present invention; and  
         [0014]      FIG. 4  is a flow chart illustrating an exemplary routine for calculating a spoke light compensation in accordance with embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0015]     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.  
         [0016]     Turning initially to  FIG. 1 , a block diagram of a video unit configured to calculate a spoke light compensation value in accordance with embodiments of the present invention is illustrated and generally designated by a reference numeral  10 . In one embodiment, the video unit  10  may comprise a Digital Light Processing (“DLP”) projection television. In another embodiment, the video unit  10  may comprise a DLP-based video or movie projector. In still another embodiment, the video unit  10  (with modifications) may be a liquid crystal diode (“LCD”) projection television or other form of projection display.  
         [0017]     The video unit  10  may comprise a light source  12 . The light source  12  may comprise any suitable form of lamp or bulb capable of projecting white or generally white light  28 . In one embodiment, the light source  12  may include a metal halide, mercury vapor, or ultra high performance (“UHP”) lamp. In one embodiment, the light source  12  is configured to project, shine, or focus the white light  28  into one static location as described further below.  
         [0018]     As illustrated in  FIG. 1 , the exemplary video unit  10  also comprises a color wheel  14  aligned in an optical line of sight with the light source  12 .  FIG. 2  is a diagram of the color wheel  14  in accordance with embodiments of the present invention. The color wheel  14  may comprise a variety of color filters  40   a,    40   b,    42   a,    42   b,    44   a,  and  44   b  arrayed as arcuate regions on the color wheel  14 . Specifically, in the illustrated embodiment, the color wheel  14  comprises color filters  40   a,    40   b,    42   a,    42   b,    44   a,  and  44   b  configured to convert the white light  28  into one of the three primary colors of light: red, green, or blue. In particular, the illustrated embodiment of the color wheel  14  comprises two red color filters  40   a  and  40   b,  two green color filters  42   a  and  42   b,  and two blue color filters  44   a  and  44   b.    
         [0019]     It will be appreciated that in alternate embodiments, the specific colors of the filters  40   a,    40   a,    42   a,    42   b,    44   a,  and  44   b  may be altered or the number of filters may be altered. For example, in one alternate embodiment, the color wheel  14  may comprise only one red color filter  40   a,  one green color filter  42   b,  and one blue color filter  44   a.  In this embodiment, the arcuate regions occupied by the color filters  44   a,    44   b,  and  44   c  may be approximately twice as long (as measured along the circumference of the color wheel  14 ) than the color filters  40   a,    42   b,  and  44   a  depicted in  FIG. 2 . In still other embodiments, the color filters  40   a,    40   b,    42   a,    42   b,    44   a,  and  44   b  may occupy either more or less of the surface area of the color wheel depending on the configuration and function of the video unit  10 .  
         [0020]     In addition, the color wheel  14  may comprise boundaries between each of the filters  40   a,    40   b,    42   a,    42   b,    44   a,  and  44   b.  These boundaries are known as spokes  46   a,    46   b,    48   a,    48   b,    50   a,  and  50   b  due to their resemblance to the spokes of wheel. For example,  FIG. 2  illustrates three types of spokes: the yellow (i.e., red-green) spokes  46   a  and  46   b,  the cyan (i.e., green-blue) spokes  48   a  and  48   b,  and the magenta (i.e., blue-red) spokes  50   a  and  50   b.    
         [0021]     Turning next to the operation of the color wheel  14 , each of the filters  40   a,    40   b,    42   a,    42   b,    44   a,  and  44   b  is designed to convert the white light  28  generated by the light source  12  into colored light  30 . In particular, the color wheel  14  may be configured to rapidly spin in a counterclockwise direction  51  around its center point  52 . In one embodiment, the color wheel  14  rotates  60  times per second. As described above, the light source  12  may be configured to focus the white light  28  at the color wheel  14 . On the opposite side of the color wheel from the light source  12 , there may be an integrator  15 , which is also referred to as a light tunnel. In one embodiment, the integrator  15  is configured to the evenly spread the colored light  30  across the surface of a Digital Micromirror Device (“DMD”)  18 . As such, those skilled in the art will appreciate that most, and possibly all, of the light that will be reflected off the DMD  18  to create video will pass through the integrator  15 .  
         [0022]     Because the integrator  15  is fixed and the color wheel  14  rotates, the light that will enter the integrator  15  can be illustrated as a fixed area  54  that rotates around the color wheel  14  in the opposite direction from the color wheel&#39;s direction of rotation. For example, as the color wheel  14  rotates in the counterclockwise direction  51 , the fixed area  54  rotates through each the filters  40   a,    40   b,    42   a,    42   b,    44   a,  and  44   b  in the clockwise direction  53 . As such, those skilled in the art will recognize that the colored light  30  entering the integrator  15  will rapidly change from red to green to blue to red to green to blue with each rotation of the color wheel  14  as the fixed area  54  passes through each of the color filters  40   a,    40   b,    42   a,    42   b,    44   a,  and  44   b.  In other words, because the light source  12  is stationary, the counterclockwise rotation of the color wheel  14  causes the fixed area  54  to rotate in a clockwise direction  53  through the colors of the color wheel. In alternate embodiments, the color wheel  14  itself may rotate in the clockwise direction  53 . Those skilled in the area will appreciate that the size and shape of the fixed area  54  is merely illustrative. In alternate embodiments, the size and shape of the fixed area  54  may be different depending on the optical design of the system.  
         [0023]     However, as the fixed area  54  passes though each of the spokes  46   a,    46   b,    48   a,    48   b,    50   a,  and  50   b,  the color of the colored light  30  entering the integrator  15  is not consistent. In particular, as the fixed area  54  crosses the edge of one particular spoke  46   a,    46   b,    48   a,    48   b,    50   a,  and  50   b,  the colored light  30  entering the integrator  15  will comprise two different colors of light. These times (when two different colors of light are entering the integrator  15 ) are referred to as spoke times. In further example, the percentage of red light will decrease and the percentage of green light will increase as the fixed area  54  moves across the spoke  46   a  into the green filter  42   a  until the colored light  30  entering the integrator  15  consists entirely of green light (i.e., the fixed area  54  crosses completely out of the red filter  40   a  and wholly into the green filter  42   a ). The color of the colored light  30  will then remain a consistent green color until the fixed area  54  crosses the spoke  48   a.    
         [0024]     Because the color of the colored light  30  entering the integrator  15  is not consistent during the spoke times, conventional DLP systems may be configured to turn off all of the micromirrors on the DMD  18  during the spoke times. However, the video unit  10  may be configured to utilize a colored light generated during the spoke times in the proper circumstances by employing a spoke light recovery (“SLR”) technique. SLR enables the video unit  10  to employ the light generated during the spoke times for a particular pixel if the shade of that particular pixel includes a red, green, and blue light levels that are each above a threshold least significant bit (“LSB”) level. In one embodiment, the video unit  10  is configured to employ SLR for a particular pixel if the red, green, and blue light corresponding to that pixel are each greater then or equal to 150 LSBs. Further, to facilitate smoother transitions from non-SLR to SLR and vice versa, the video unit may be configured to subtract some portion of the light generated during the non-spoke times to compensate for the additional light output during the spoke times. This compensation factor is referred to as the spoke light compensation value. As will be described further below with regard to  FIGS. 3 and 4 , the video unit  10  may be configured to dynamically calibrate its spoke light compensation value.  
         [0025]     Returning now to  FIG. 1 , the video unit  10  may also comprise a digital light processing (“DLP”) circuit board  16  arrayed within an optical line of sight of the integrator. The DLP circuit board  16  may comprise the DMD  18  and a processor  20 . As described above, the DMD  18  may comprise a multitude of micromirrors mounted on microscopic, electrically-actuated hinges that enable the micromirrors to tilt between a turned on position and turned off position. In the illustrated embodiment, the DMD  18  is also coupled to the processor  20 . In one embodiment, the processor  20  may receive a video input and, as described in greater detail below, direct the micromirrors on the DMD  18  to turn on or off, as appropriate to create the video image. In alternate embodiments the processor  20  may be located elsewhere in the video unit  10 .  
         [0026]     The colored light  30  that reflects off a turned on micromirror (identified by a reference numeral  34 ) is reflected to a projecting lens assembly  24  and then projected on to a screen  28  for viewing. On the other hand, the colored light that reflects off of a turned off micromirror (identified by a reference numeral  32 ) is directed somewhere else in the video besides the screen  26 , such as a light absorber  22 . In this way, the pixel on the screen  26  that corresponds to a turned off micromirror does not receive the projected colored light  30  while the micromirror is turned off.  
         [0027]     As illustrated in  FIG. 1 , the video unit  10  may also include a photodiode assembly  26 . In one embodiment, the photodiode assembly  26  may be mounted in the overscan region of the video unit  10 . In alternate embodiments, however, the photodiode assembly  26  may be located in other suitable locations within the video unit  10 . As illustrated in  FIG. 1 , the photodiode assembly  26  may be communicatively coupled to the processor  20 . As such, in one embodiment described in greater detail below, the processor  20  may be configured to initiate and/or control a spoke light compensation calibration routine (see  FIG. 4 ) and to receive and/or calculate a spoke light compensation value.  
         [0028]      FIG. 3  is a diagram of the photodiode assembly  26  in accordance with one embodiment. As will be described further below, the photodiode assembly  26  may be configured to execute a spoke light compensation calibration routine to calculate a spoke light compensation value for the video unit  10  to use when SLR is employed. As illustrated in  FIG. 3 , the photodiode assembly  26  may include a red photodiode  68   a,  a green photodiode  60   b,  and a red blue photodiode  60   c.  As will be appreciated, the photodiodes  60   a, b,  and  c  may be configured to convert received light into a voltage based on the brightness of the light. In particular, the red photodiode  60   a  may be configured to detect red light and to convert the detected red light into a voltage based on the brightness of the detected red light. Similarly, the photodiode  60   b  and  60   c  may be configured to convert detected levels of green light and blue light respectively into voltages.  
         [0029]     The voltages produced by the photodiode  60   a, b,  and  c  may be transmitted to operational amplifiers  62   a,    62   b,  and  62   c,  which may amplify the voltages. The amplified voltages can then be transmitted to an analog/digital converter  64 , which converts the analog voltages produced by the photodiodes  60   a, b,  and  c  and amplified by the operational amplifier  62   a, b,  and  c  into digital values. The analog/digital converter  64  may then output the digital values to a comparison circuit  66 , which is configured to determine spoke light compensation values  68  for red light, green light, and blue light based on as will be described further below with regard to  FIG. 4 .  
         [0030]     Turning next to  FIG. 4 , a flow chart of an exemplary spoke light compensation calibration routine  70  in accordance with one embodiment is illustrated. In one embodiment, the routine  70  may be performed by the video unit  10 . As illustrated in  FIG. 4 , the routine  70  may begin by illuminating the photodiode assembly with red, green, and blue spoke light, as illustrated in block  72 . Next, the photodiode assembly  26  may read voltages from the photodiodes corresponding to the brightness of the red, green, and blue spoke light, as indicated in block  74 . Once read, the video unit  10  may store the voltages corresponding the spoke light from the photodiodes in a memory located within the photodiode assembly  26 , on the DLP circuit board  16 , or in another suitable location within the video unit  10 , as indicated in block  76 .  
         [0031]     The video unit  10  may also illuminate the photodiodes within the photodiode assembly  26  using non-spoke light, as indicated by block  78 . As the photodiodes in the photodiode assembly  26  are illuminated, the photodiode assembly  26  may read the corresponding voltages from the photodiodes  60   a,    60   b,  and  60   c,  as indicated in block  80 . Next, the comparison circuit  66  may compare the voltages corresponding to the non-spoke light to the stored voltages of the spoke light, as indicated in block  82 .  
         [0032]     If the voltages corresponding to the non-spoke light do not match the stored voltages corresponding to the spoke light (block  84 ), the video unit  10  may adjust the non-spoke light level and repeat blocks  78 - 84  until the voltage corresponding to the non-spoke light matches the stored voltage from the spoke light to within a margin of error, as indicated in block  86 . For example, if the non-spoke light voltage was greater than the spoke light voltage, the video unit  10  may decrease the spoke light level (i.e., decrease the non-spoke LSBs). Similarly, if the spoke light voltage is greater than the non-spoke light voltage, the video unit  10  may increase the non-spoke LSBs to increase the amount of non-spoke light.  
         [0033]     Once the two voltages match, the video unit  10  may set the spoke light compensation value equal to the light level (e.g., the LSBs) of the non-spoke light, as indicated in block  88 . Once set, the spoke light compensation value can be employed when the video unit  10  uses SLR.  
         [0034]     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.