Pre-subpixel rendered image processing in display systems

Abstract

Display systems and image processing methods process pre-subpixel rendered images embedded in input color image data. The display systems include a pre-subpixel rendered (P-SPR) image detector that detects locations of a marking code that marks the portion of the input data that has been pre-subpixel rendered and which is ready for direct display. Several display system embodiments comprise first and second image data paths; the input data that requires sub-pixel rendering proceeds along the first path while the P-SPR image data proceeds along the second path. Another display system embodiment processes the combined input and P-SPR data along a single data path. Techniques for marking and detecting P-SPR image data using two distinct marking codes are presented in the context of the sub-pixel layout of the display. Techniques for using P-SPR data to display high-quality graphical symbols (e.g., font glyphs) are suitable for small, low-cost devices.

What is claimed is: 
     
         1 . An image processing method for rendering characters in a font onto a display device having a sub-pixel layout and capable of detecting pre-subpixel rendered image data; the method comprising:
 performing a sub-pixel rendering operation on image data values representing each character in the font to produce pre-subpixel rendered glyph image data indicating a glyph ready for display on the display device;   marking the pre-sub-pixel rendered glyph image data with a marking code to produce marked pre-subpixel rendered glyph image data; the marking code distinguishing the pre-subpixel rendered glyph image data from image data that has not been sub-pixel rendered;   storing the marked pre-subpixel rendered graphical symbol image data in a memory device; and   in response to a signal requesting display of a character in the font, outputting the marked pre-subpixel rendered glyph image data indicating the character to the display device.   
     
     
         2 . The image processing method of  claim 1  further comprising storing marked pre-subpixel rendered glyph image data indicating a version of each glyph for each logical pixel in the sub-pixel layout of the display at which a rendered glyph may be positioned. 
     
     
         3 . The image processing method of  claim 1  further comprising storing marked pre-subpixel rendered glyph image data indicating a version of each glyph for each sub-pixel in the sub-pixel layout of the display at which a rendered glyph may be positioned. 
     
     
         4 . The image processing method of  claim 1  further including, when outputting the pre-subpixel rendered glyph image data indicating the character to the display device, adding marked image data to the marked pre-subpixel rendered glyph image data in order to position a rendered glyph at one of a sub-pixel or logical pixel starting position. 
     
     
         5 . The method of  claim 1  wherein the font is an outline font and each character in the font is defined as a set of lines and curves. 
     
     
         6 . An image processing method for displaying a pre-subpixel rendered glyph stored in a memory device as a density map of pixels each indicating density values specifying a mixing percentage of each of a foreground color and a background color; the method comprising:
 receiving an input signal to display the pre-subpixel rendered glyph;   retrieving the pre-subpixel rendered glyph from the memory device;   for each pixel of the pre-subpixel rendered glyph, combining the mixing percentages of an input foreground color value and an input background color value according to the density values stored in the density map to produce color image data values indicating a blended color glyph; and   outputting the color image data values indicating the blended color glyph directly to a display device without further sub-pixel rendering.   
     
     
         7 . The image processing method of  claim 6  wherein the input foreground color value and the input background color value are specified in a linear color space. 
     
     
         8 . The image processing method of  claim 6  further including performing a gamut mapping operation on the input foreground color value and the input background color value to produce image data values specified in a color space of the display device. 
     
     
         9 . The image processing method of  claim 6  further including, when one of the input foreground color value and the input background color value is specified between a full-off black color and a full-on bright color, performing an input gamma operation to at least one of the input foreground color value and the input background color value to produce linear color space values prior to combining the mixing percentages of the input foreground color value and the input background color value. 
     
     
         10 . The image processing method of  claim 6  wherein the input signal to display the pre-subpixel rendered glyph signal includes the foreground color value and the background color value. 
     
     
         11 . The image processing method of  claim 6  wherein the input signal to display the pre-subpixel rendered glyph signal includes the input foreground color value; and wherein the image processing method further includes determining the input background color value from a destination image region in a target output image to be displayed on the display device. 
     
     
         12 . The image processing method of  claim 11  wherein the blended color glyph is displayed in the destination image region of the target output image such that the blended color glyph overlays the destination image region. 
     
     
         13 . The image processing method of  claim 11  wherein determining the input background color value from the destination image region in the target output image includes:
 retrieving an input source image data subset from an input source image from which the target output image was produced; the input source image data subset corresponding to the destination image region in the target output image; 
 performing a gamut mapping operation on the input source image data subset to produce gamut-mapped source image data indicating color values specified in a color space of the display device; and 
 performing a sub-pixel rendering operation gamut-mapped source image data to produce the input background color value. 
 
     
     
         14 . The image processing method of  claim 11  wherein determining the input background color value from the destination image region in the target output image comprises retrieving the input background color value from a frame buffer in the display device. 
     
     
         15 . The image processing method of  claim 6  correcting the color image data values indicating the blended color glyph for output gamma prior to outputting the blended color glyph. 
     
     
         16 . The image processing method of  claim 6  wherein the display device is capable of detecting pre-subpixel rendered image data, and wherein the method further includes, prior to outputting the blended glyph directly to the display,
 marking the blended glyph with a marking code; and 
 embedding the marked blended color glyph in an image data stream; the marking code identifying the blended color glyph to the display as pre-subpixel rendered image data ready for display without further sub-pixel rendering.