System and method for dithering and for the quantization of image data for the optimization of the visual quality of a recovered image

摘要

A color graphics pipeline has a separate encoder with a dither table for processing each color value in pixel data received from a host processor or rasterizer. The encoders modify color values and dither noise values and also combine both positive and negative dither noise values with the color values, for independent optimization of each color and for better edge detection in a color recovery filter within a decoder of the pipeline. Each encoder comprises the following elements. A comparator mechanism compares a color value with a predetermined cutoff value. A dither table provides dither noise values. An offset mechanism modifies the dither noise values to derive a modified dither noise value when the color value is greater than or equal to the predetermined cutoff value. An aliasing mechanism aliases the color value with other color values below the predetermined cutoff value to derive an aliased color value when the color value is less than the predetermined cutoff value. An adder mechanism adds the unmodified dither noise or modified dither noise to the aliased color value or nonaliased color value, respectively, to derive the dithered color value. A clamping mechanism ensures that the dithered color value resides within a predetermined color range. Finally, a quantizing mechanism quantizes the dithered color value to derive a quantized/dithered color value for storage in memory, such as in a frame buffer.