Abstract:
The invention provides a method and system for reducing distortion in images provided by display systems employing Spatial Light Modulating elements is provided. A method comprises steps of providing a set of pixel values corresponding to pixels of an image to be displayed. The number of pixel values comprising the set is greater than the number of available SLM elements. At least some of the pixel values are adjusted to provide a set of adjusted pixel values. At least a first set of pixels and a second set of pixels are generated from the set of adjusted pixel values. The image is displaying as a matrix of pixels comprising the first set of pixels and the second set of pixels. At least one of the pixels of the first set overlaps at least one of the pixels of the second set and the adjusting step is carried out by adjusting pixel values of the pixel data set to compensate for image distortion due to overlapping pixels of the matrix.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit, under 35 U.S.C. § 365 of International Application PCT/US2005/009621, filed Mar. 22, 2005, which was published in accordance with PCT Article 21(2) on Oct. 6, 2005 in English and which claims the benefit of U.S. provisional patent application No. 60/555,253 filed Mar. 22, 2004. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to Spatial Light Modulation (SLM) display systems, and in particular to filters and filter methods for use in SLM systems. 
     BACKGROUND OF THE INVENTION 
     Spatial Light Modulating (SLM) systems include Digital Light Processing™ (DLP™) systems. DMD and DLP™ are trademarks of Texas Instruments Corporation. Recent developments in SLM technology rely on SLM elements that provide diamond shaped pixels instead of square shaped pixels. Processing techniques for SLM systems include a so called “smooth pixel” processing technique. According to the smooth pixel technique, a displayed image is formed by combining a first set of pixels with a second set of pixels. The second set is displaced from the first set. The combined first and second pixel sets form a displayed image. 
     In one example SLM system, an SLM array comprising a number of SLM elements provides first and second pixel sets for each incoming picture, or frame, to be displayed. The combined pixels from the first and second pixel sets provide more displayed pixels than the number of SLM elements employed to provide the pixel sets. 
     However, a drawback is associated with this technique. Pixels of the first and second pixel sets overlap in the displayed image. At least some of the pixels from the first set effectively overlap at least some of the pixels from the second set. As a result, when the pixel sets are displayed together so as to form an image, light in the regions of overlapping pixels is a combination of light from each of the overlapping pixels. This sometimes results in brighter than intended, or less bright than intended image portions. 
     Thus, some loss of image quality is incurred with this technique as compared to other display techniques. Accordingly, image processing devices and methods are needed that account for distortion due to overlapping pixels in displayed pixel sets of SLM devices. 
     SUMMARY OF THE INVENTION 
     According to various embodiments of the invention methods and systems for reducing distortion in images provided by display systems ( 100 ) employing Spatial Light Modulating (SLM) elements are provided. A method according to one embodiment of the invention comprises steps of providing a set ( 620 ) of pixel values corresponding to pixels of an image to be displayed. The number of pixel values comprising the set is greater than the number of available SLM elements. At least some of the pixel values are adjusted to provide a set of adjusted pixel values ( 678 ). At least a first set of pixels and a second set of pixels are generated from the set of adjusted pixel values. The image is displayed as a matrix of pixels ( 450 ) comprising the first set of pixels ( 410 ) and the second set of pixels ( 430 ). At least one of the pixels of the first set overlaps at least one of the pixels of the second set and the adjusting step is carried out by adjusting pixel values of the set of pixel values to compensate for image distortion due to overlapping pixels of the matrix. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be described below in more detail, with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a display system including an array of spatial light modulation (SLM) elements suitable for implementing various embodiments of the invention. 
         FIG. 2  is a block diagram illustrating in more detail the electronics subsystem of the display system illustrated in  FIG. 1 . 
         FIG. 3  is a block diagram illustrating an SLM system including a pixel filter according to an embodiment of the invention. 
         FIG. 4  is a diagram illustrating relationship between received pixel data, adjusted pixel data and a pixel matrix according to an embodiment of the invention. 
         FIG. 5  is a block diagram of a pixel filter according to an embodiment of the invention. 
         FIG. 6  illustrates an example lookup table suitable for use in the pixel data filter of  FIG. 5  according to an embodiment of the invention. 
         FIG. 7  is a detailed diagram of an embodiment of the pixel data processing device illustrated in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Spatial Light Modulator (SLM) devices find increasing use in a wide range of imaging applications such as video image projection and printing. Typical spatial light modulators include devices such as Liquid Crystal Devices (LCDs) and digital micro-mirror devices (DMDs™). A typical spatial light modulator comprises a two-dimensional array of modulator elements that operate upon incident light in order to form a two-dimensional image on a display surface. LCD based devices use light polarization characteristics in order to modulate each light element in the array. DMD™ based devices use an array of tiny micro-mirrors to modulate individual light elements. Each element in a spatial light modulator array exhibits a variable light intensity in response to a corresponding drive voltage level. In one embodiment of the invention, each element in an SLM array corresponds to at least one pixel of a displayed image. 
       FIG. 1  is a pictorial diagram illustrating an example system  100  including a Spatial Light Modulating (SLM) array  500  suitable for implementing various embodiments of the present invention. System  100  comprises at least one light source  301  coupled to an optical system  400 . Optical system  400  comprises relay and illumination optics  300  and projection optics  200 . Optical system  400  includes at least one array  500  of spatial light modulating elements  502 . According to an embodiment of the invention array  500  comprises a semiconductor-based array of reflective light elements  502 . According to one embodiment of the invention, SLM array  500  comprises a binary Pulse Width Modulated (PWM) array  500  of light switching elements  502 . In one embodiment, elements  502  of PWM array  500  comprise micro-electromechanical system (MEMS) devices, for example, mirrors of a Digital Micromirror Device™ (DMD)™. 
     An electronics subsystem  600  includes an input for receiving a video signal  601  and an output coupled to the SLM array  500 . Electronics subsystem  600  processes incoming video signal  601  so as to provide PWM signals to drive elements  502  of array  500 . The PWM signals control the angle and dwell time of elements  502  of array  500  in accordance with pixel values provided by video signal  601 . Properties, for example, brightness, of pixels displayed on display screen  499  are related to the dwell time of respective corresponding micro-mirror elements  502 . 
     Electronics subsystem  600  receives a video signal  601  from a source of video signals (not shown). Video signal  601  comprises video image data corresponding to video images to be projected and displayed on display device  499 . Electronics subsystem  600  processes video signal  601  and provides a processed video signal  602  to drive array  500 . 
     Optics system  400  comprises at least one relay and illumination optics portion  300 , at least one projection optics portion  200  and at least one light source  301 . Light from light source  301  is transmitted through at least one relay optics portion  300 . Light from relay optics portion  300  is projected onto light reflecting elements  502  of SLM array  500 . 
     According to embodiments of the invention, video signal  601  is provided by at least one of a wide variety of suitable video signal sources. Suitable video signal sources include for various embodiments of the invention are too numerous to recite in total. However, some examples include, but are not limited to, digital versatile disk (DVD) systems, set top boxes, broadcast video sources, Internet video sources, cable video sources, satellite video sources, wireless and telephonic sources, to name but a few. Embodiments of the invention comprise digital video intermediate systems wherein video sources include film, telecines, video masters and the like. 
     Regardless of video signal source, suitable video signals  601  for embodiments of the invention include, among others, analog video signals, digital video signals, component video signals and composite video signals. Suitable signal formats include, among others, National Television Standards Committee (NTSC) format, Phase Alternate Lines (PAL) format, and PAL plus format. Any video format providing pixel values corresponding to pixels of an image to be displayed is suitable for use in various embodiments of the invention. 
       FIG. 2  illustrates functional blocks of the electronics subsystem  600  illustrated in  FIG. 1  according to an embodiment of the invention. Electronics subsystem  600  comprises a receiver  610  for receiving video signal  601 . Receiver  610  is coupled to video processing unit  640 . Video processing unit  640  is coupled to SLM array driver  690 . 
     According to embodiments of the invention, receiver  610  receives video signal  601  at an input. In an example embodiment of the invention, receiver  610  decodes video signal  601  and performs Analog to Digital (A/D) conversion, Luminance-chrominance separation (Y/C separation), and chrominance demodulation of video signal  601  in accordance with conventional video signal receiving and decoding techniques, 
     According to embodiments of the invention, video processing unit  640  further provides video processing functions, for example, progressive scan conversion, and resampling of video signal  601  in accordance with conventional techniques. Video processing unit  640  is coupled to an SLM device driver  690 . SLM device driver  690  provides drive signals for driving elements  503  of SLM array  500 . According to an embodiment of the invention, video processor provides enhanced Chrominance (2C) and Luminance (2Y) signals for use by driver  690  in driving elements  503  of array  500  so as to modulate light in accordance with video signal  601 . 
     Video processing unit  640  includes pixel filter  320  coupled to a pixel group generator  680 . In one embodiment of the invention, pixel group generator  680  is a conventional device providing pixel groups for so called, “smooth pixel” processing techniques. According to one embodiment of the invention, pixel filter  320  is implemented by programming a processor of video processing unit  640  so as to implement pixel processing functions in accordance with the various embodiments of the invention described herein. In alternative embodiments of the invention, functions of pixel filter  320  are provided by hardware without the need for programming a processor. Still other embodiments of the invention implement some functions of pixel filter  320  in hardware while other functions are implemented by a processor programmed for carrying out the other functions. However, as those of ordinary skill in the art will readily appreciate upon reading the specification herein, a wide variety of hardware and software combinations will be suitable for implementing the invention. Therefore, the pixel filter of the invention is not limited to one specific hardware and processor arrangement. 
     According to one embodiment of the invention, receiver portion  610  provides luminance (Y) signals  620  to pixel filter  320  based upon video signal  601 . According to one embodiment of the invention, receiver portion  610  provides chrominance (C) signals  649  to pixel filter  320  based upon video signal  601 . 
     In some embodiments of the invention, video signal processor  640  provides further processing functions including, for example, color space conversion, gamma correction removal, error diffusion, on screen display capability, Red, Green, Blue (RGB) input receiving capability, and user operable image controls. In one embodiment of the invention, driver  690  includes a Field Programmable Gate Array (FPGA). 
     In one embodiment of the invention Field Programmable Gate Array (FPGA)  690  receives RGB video signals from video signal processor  640  and provides PWM control functions, image reformatting, bit plane conversion and DMD drive signal functions based, at least in part, on the RGB video signals. According to embodiments of the invention, system  600  further comprises memory  622  and timing and control circuits  621  for electronics subsystem  600 . 
     As will be readily appreciated by those of ordinary skill in the art processors are commonly embedded throughout systems in a wide variety of configurations and capabilities. Any processor configuration implementing the inventive circuits, systems and methods described herein remain within the scope of the invention. 
       FIG. 3  is a block diagram illustrating an embodiment of the invention. Display screen  499  is arranged with respect to SLM array  500  so as to display an image comprising a matrix  450  of pixels. Matrix  450  comprises at least a first pixel group  410  and a second pixel group  430 . (also illustrated in  FIG. 4 ). According to alternative embodiments of the invention, matrix  450  comprises more than two pixel groups. According to an embodiment of the invention, the number of pixels comprising matrix  450  is greater than the number of elements  502  of SLM array  500  used to provide first and second pixel groups  410  and  430 . 
     As illustrated in  FIG. 3 , light from a light source  301  is transmitted through relay optics subsystem  300 . In one embodiment of the invention, optics subsystem  300  includes a means for providing colored light. According to one embodiment of the invention, optics subsystem  300  includes a color wheel alternately producing red, green and blue light. According to an alternative embodiment of the invention, light source  301  comprises a red light source, a green light source and a blue light source. The colored light is projected onto array  500  and reflected from array  500 . Light reflected from array  500  is provided to display  499  via projection optics subsystem  200 . 
     Elements  502  of array  500  are driven in accordance with pixel values provided by pixel data set  620 . Each pixel of matrix  450  corresponds to a pixel value of incoming pixel data set  620 . Pixel data set  620  is generated based upon video signal  601 . In  FIG. 3  pixel data set  620  is represented by an arrangement of letters A through O. 
     Pixel processor  320  adjusts pixel values of pixel data set  620  and provides adjusted pixel data set  678  to pixel group generator  675 . In  FIG. 3  adjusted pixel data set  678  is represented by an arrangement of letters A′ through O′. Pixel group generator  675  separates adjusted pixel data set  678  into first and second pixel data groups ( 679  and  680 ). In one embodiment of the invention, pixel group generator  675  operates in accordance with a known pixel processing technique such as a “smooth pixel” processing technique. According to smooth pixel processing, an input pixel data set, for example,  620  is separated into first and second pixel data groups. The first and second pixel data groups provide first and second pixel groups comprising a displayed matrix. 
     However, conventional pixel processing techniques do not include pixel filter  320 , nor do conventional systems provide an adjusted pixel data set  678  to a pixel generator  675 . Accordingly, first and second pixel groups  410  and  430  comprising matrix  450  according to the invention provide significant advantages over conventional smooth pixel processing techniques. 
       FIG. 4  illustrates the relationship between pixel data set  620 , adjusted pixel data set  678 , pixel data groups  679  and  680 , pixel groups  410  and  430 , and pixel matrix  450  according to an embodiment of the invention. As illustrated in  FIG. 4 , first pixel group  410  comprises rows h and columns c of adjacent pixels  412 . For convenience, a single indicator  412  indicates individual pixels of group  410 . Second pixel group  430  comprises rows h and columns c of adjacent individual pixels  432 . 
     Pixel groups  410  and  430  are projected onto display screen  499  so as to appear displaced from each other, for example, by a distance d. In one embodiment of the invention, pixel groups  410  and  430  are displaced from each other in a direction substantially in x-direction of the plane of the surface of display screen  499 . 
     In one example embodiment of the invention, second pixel group  430  is displayed spaced from first pixel group  410  by a distance equal to about half of the height of a single pixel. The resulting pixel matrix  450  therefore comprises overlapping pixels. In other words, individual pixels from first pixel group  410 , overlap individual pixels from second pixel group  430 . 
     In one embodiment of the invention, SLM elements  502  comprise diamond shaped elements. Therefore, pixels of matrix  450  comprise substantially diamond shaped pixels (example illustrated in  FIG. 4 ). However, other pixel shapes, e.g. square pixels, are known, and are suitable for some applications of the invention. 
       FIG. 3  illustrates an optical element  210  as one example of conventional means for providing the spacing for pixel groups  410  and  430 . Optical element  210  reflects one of pixel sets  410  and  430  onto screen  499  at a first angle Ø 1 . Optical element  210  subsequently projects the other pixel set at a second angle Ø 2 . This technique has the advantage of providing a matrix  450  with more displayed pixels than the number of available elements  502  on SLM device  500 . In one embodiment of the invention, the number of pixels comprising matrix  450  is about twice the number of available micro-mirrors  502  of SLM device  500 . 
     However, the technique described above results in overlapping pixels. Light from each of the overlapping pixels combines. Therefore, the displayed brightness for a given pixel sometimes fails to correspond to the brightness value provided in pixel data set  620 . In some cases the displayed brightness of overlapping pixels is greater than the intended brightness. In other cases, the displayed brightness of overlapping pixels is less than the intended brightness. 
     According to an embodiment of the invention pixel data set  620  is provided to pixel filter  320 . Filter  320  provides modified pixel data set  678 . Pixel data groups  679  and  680  are formed from modified pixel data set  678 . The pixel values of pixels of pixel data groups  679  and  680  are used to generate pixel groups  410  and  430  respectively. Displayed combined pixel groups  410  and  430  comprise matrix  450 . 
     In accordance with an embodiment of the invention, pixel filter  320  provides adjusted example data set  678  as represented by the following diagram: 
     
       
         
           
             
               
                 
                   A 
                   ′ 
                 
               
               
                 
                   B 
                   ′ 
                 
               
               
                 
                   C 
                   ′ 
                 
               
               
                 
                   D 
                   ′ 
                 
               
               
                 
                   E 
                   ′ 
                 
               
             
             
               
                 
                   F 
                   ′ 
                 
               
               
                 
                   G 
                   ′ 
                 
               
               
                 
                   H 
                   ′ 
                 
               
               
                 
                   I 
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                   J 
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                   K 
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                   L 
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                   M 
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                   N 
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                   O 
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     First pixel data group  679  comprises pixel data labeled A′, C′, E′, G′, I′, K′, M′, O. Second pixel data group  680  comprises pixels labeled B′, D′, F′, H′, J′, ′L, N′. Pixel groups  410  and  430  are generated based on pixel data groups  679  and  680  respectively. Matrix  410  comprises first pixel group  410  and second pixel group  430 . 
     As can be seen from the drawing of matrix  450 , pixels from the first pixel group  410  at least partially overlap pixels of pixel group  430  and vice versa. For example, the G pixel position in the first pixel group  410  is overlapped by the B, F. L and H pixel positions from the second pixel group  430 . This overlap causes intensity distortion of the image represented by matrix  410 . 
     According to an embodiment of the invention, distortion in pixel intensity caused by the overlap is reduced by an image enhancing filter arrangements  320  illustrated in  FIGS. 3 ,  5  and  7 . 
       FIG. 5  illustrates an embodiment of a pixel filter  320  according to an embodiment of the invention. Pixel filter  320  comprises at least one two-dimensional filter that operates on respective pixels of pixel data set  620  in accordance with an array h given by: 
     
       
         
           
             
               
                 
                     
                 
               
               
                 
                   - 
                   α 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   - 
                   α 
                 
               
               
                 β 
               
               
                 
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                   α 
                 
               
             
             
               
                 
                     
                 
               
               
                 
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             wherein β is a scaling factor associated with a pixel of pixel data set  620  from which the intensity distortion is to be removed; and 
             α is a scaling factor for pixels overlapping the pixel of pixel data set  620  from which the intensity distortion is to be removed.
           More particularly, filter  320  adjusts intensity values I of respective pixels of data set  620  by an amount sufficient to compensate for the intensity contribution of pixels overlapping a respective pixel in matrix  450 . For example, in  FIG. 4 , the intensity (I G ) of pixel G in pixel data set  620  is scaled by an amount (β) such that the intensity distortion caused by overlapping pixels B (I B ), F (I F ), L (I L ) and H (I H ) in displayed matrix  450  is reduced. In an embodiment of the present invention, adjusted pixel G′ has an adjusted intensity value I G′  in accordance with the relationship illustrated below:
 
 I   G′ =β( I   G )−α( I   H   +I   L   +I   B   +I   F )  (1)
   
         
             Wherein: 
             β is a scaling factor associated with the pixel G from which the intensity distortion is to be removed; and 
             α is a scaling factor associated with overlapping pixels that are contributing to the intensity of pixel G. 
           
         
       
    
     According to one embodiment of the invention, a relationship between β and α is given by: β=1+4α. This relationship provides unity DC gain. However, the invention is not limited in this regard. In one embodiment of the invention, α is approximately +⅛ and β is approximately 3/2. Selecting these example scaling factors has been found to provide unity DC gain while compensating for distortion in some embodiments of the invention. 
     According to the example above, the pixel data for the example data set  620 , and the adjusted data set  678  is represented as follows: 
     
       
         
           
             
               
                 
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       FIG. 5  is a block diagram illustrating an example filter arrangement  320  representing one of three like filters  320   a ,  320   b ,  320   c  illustrated in  FIG. 3 . Filter  320  implements the relationship described in equation 1 above for each pixel in respective red, green and blue components of component video signal  620 . For convenience, the operation of one filter  320  will be described in relation to an example pixel G. Overlapping pixel groups  410  and  430  as shown in  FIG. 4  are referred to herein as an example for purposes of discussion. However, it will be understood that each of the pixels comprising incoming pixel set  620  are suitable for processing in the same way to remove intensity distortion caused by overlapping pixels. 
     Referring to  FIG. 5 , a pixel filter  320  according to an embodiment of the invention is illustrated. Pixel filter  320  comprises a delay circuit  646 . Delay circuit  646  receives pixel data of pixel data set  620 . Delay circuit  646  delays the received pixel data so as to provide pixel data for a plurality of pixels substantially simultaneously. In the example illustrated in  FIG. 5 , delay circuit  646  provides pixel data for pixels H, L, F and B (overlapping example pixel G in matrix  450 .) to adder  648 . At the same time, delay circuit  646  provides data for example pixel G to a second scaler  652 . Adder  648  provides an output representative of the sum of pixel values for pixels H, L, F and B to a first scaler  651 . First scaler  651  applies a scaling factor α to its input to provide a scaled output. Second scaler  652  applies a scaling factor β to its input to provide a scaled output. The scaled outputs of scalers  651  and  652  are combined by subtractor  653 . The difference output of subtractor  653  represents an adjusted value G′ for example pixel G. According to one embodiment of the invention, the difference output of subtractor  653  is optionally provided to a limiter. In that case, successive output values provided by limiter  654  comprise adjusted pixel data set  678 . 
     According to one embodiment of the invention, a scaling factor for first scaler  655  is adjustable by an adjustment factor X provided by first adjuster,  655 . According to one embodiment of the invention, a scaling factor for the second scaler  652  is adjustable by an adjustment factor Y provided by second adjuster  657 . 
       FIG. 6  illustrates a pixel filter control circuit  700  for implementing an embodiment of pixel filter  320  including adjustable scaling factors. Filter control circuit  700  comprises a look up table  150 . Look up table  150  stores a plurality of selectable XY pairs of adjustment factors for X  154  and Y  156 . Each XY pair of the table corresponds to one of the filter control setting  152  of table  150 . In the example illustrated in  FIG. 6 , eight possible filter control settings, e.g., 0 through 8 are provided. To select scaler adjustment factors X and Y a filter control signal representing one of the eight control settings is provided at filter control input  688  of table  150 , The XY value pair corresponding to the filter control setting selected by input  688  provides adjustment factors X and Y to first and second adjusters  655  and  657 . In that manner, lookup table  150  provides adjustable scaling factors for scalers  655  and  652 . 
     In one embodiment of the invention, the X and Y values of table  150  maintain a given relationship between scaling factors α and β while permitting adjustment of scaling factors α and β. In one embodiment of the invention, the given relationship between α and β is a unity gain relationship given by:
 
β=1+α.
 
       FIG. 7  is a more detailed diagram of one embodiment of the filter illustrated in  FIG. 6 . A video signal representing pixel data set  620  is provided to full line delay registers  803  and  805 . Line delay registers  803  and  805  delay the video signal by an entire line of displayed video according to one embodiment of the invention. For the purpose of the present example, the delays of line delay registers  803  and  805  are chosen according to the principles illustrated by the following example. When the data for pixel M, for example, is presented at input  620 , the output of line delay register  805  will be H and the output of line delay register  803  will be C. As illustrated in  FIG. 7 , the output of line delay registers  805 ,  803  and the original video input signal, e.g., M are coupled respectively to a second bank of delay registers  807 ,  809 , and  800 . The outputs of delay registers  803  and  800  are added by adder  812 . The output of adder  812  is provided to a first input of adder  823 . 
     A second input to adder  823  is provided as follows. An output of delay element  809  is provided to delay element  811 . The output of delay element  811  is provided to one input of adder  813 . The other input to adder  813  is provided by the output of delay element  807 . A sum output of adder  813  is coupled to the second input to adder  823 . 
     According to the example above, the sum H+L+B+F is provided. Pixels H, L, B and F are pixels overlapping pixel G in matrix  450  of  FIG. 1 . This sum represents a sum of pixel intensity values for each of the pixels that overlap pixel G. The sum H+L+B+F is then scaled by a scaling factor α. Scaling is accomplished in one embodiment of the invention as follows. The sum H+L+B+F is provided to multiplier  814 . Multiplier  814  multiplies the sum H+L+B+F accordance with a first multiplier X, indicated at multiplier input  655 . The output of multiplier  655  is provided to divider  651 . In the embodiment illustrated In  FIG. 7  divider  651  divides the output or multiplier  655  by 32. Therefore, the sum (H+L+B+H) output from adder  823  is scaled by a factor of x/32, where 32 is a constant and x/32 comprises scaling factor α. For example if x=4 in  FIG. 7 , then a= 4/32 or ⅛. Accordingly, the scaled sum for pixels in the example above is (⅛) (H+L+B+F). 
     Similarly, a second scaling factor β is applied to pixel data value G by providing data value G to multiplier  804 . The output of multiplier  804  is provided to a ⅛ divider  652 . Therefore, G is scaled by a factor of y/8 comprising scaling factor β. A subtractor  817  provides an output representing the difference between the scaled pixel intensity data value β(G) and the scaled sum of the intensity values of overlapping pixels, i.e., (α) (H+L+B+F). 
     In one embodiment of the invention the output of subtractor  817  is provided to a limiter  654 . Limiter  654  maintains the difference value provided by subtractor  817  within a range of pixel intensity values. According to one embodiment of the invention, various additional delay registers, e.g.,  819  are provided in the filter circuit in  FIG. 7  to allow for circuit settling times. 
     It will be appreciated by those of ordinary skill in the art that various other relationships between β and α, e.g., other than unity gain relationships, are possible. Table  600  is suitable for implementing a wide variety of relationships. The other relationships can readily be accomplished by substituting appropriate values of x y pairs in table  600 . Advantageously the pairs are customizable such that a specific relationship is maintained between β and α for all values of x and y pairs on the table. 
     According to one embodiment of the invention, look up table  150  is implemented in a memory (not shown), for example, a semiconductor memory. In that case, the memory stores values of x and y. The memory includes x and y outputs coupled to inputs x (indicated at  655 ) and y (indicated at  657 ) respectively of filter  645  of  FIG. 7 . In a look up table embodiment comprising eight x,y pairs, x is selectable such that α ranges in 1/32 increments between 0 to 7/32. For the same table, y is selectable such that β ranges from 1 to 15/8 in increments of ⅛. 
     Those skilled in the art will readily appreciate that the foregoing filters are capable of implementation in various combinations of software, hardware and/or firmware. According to one embodiment of the invention, look up table values are stored in an electronic memory. For example, data sets can be stored in a bus register, RAM or other data storage device associated with a DLP system microprocessor. Still, the invention is not limited in regard to memory types, and other suitable methods exist for storing such values. In one embodiment of the invention, filter control values are selectable by a user via a user operable interface with a DLP display system. According to another embodiment of the invention, filter control values are automatically adjusted by a system microprocessor (not shown) provided for controlling the DLP system. 
     Further, while  FIGS. 5 and 7  represent embodiments of filters according to the invention, those skilled in the art will recognize that the invention is not limited to particular component arrangements. For example, other filter architectures are possible for implementing the invention. That is, other filter architectures are suitable for operating on pixel values so as to adjust pixel intensity to at least partially compensate for the intensity distortion caused by overlapping pixels. Further, while it is be advantageous in many embodiments of the invention to select β=1+4α, the invention is not limited in this regard to such values. The values of β and α are selectable to have other values and relationships according to various embodiments of the invention.