System and method for dithering and quantizing image data to optimize visual quality of a color recovered image
First Claim
1. A system for dithering and quantizing image data, comprising:
- dithering means for providing a dither noise value;
comparator means for comparing a color value corresponding with the image data with a predetermined cutoff value;
aliasing means for aliasing the color value with other color values below said predetermined cutoff value when the color value is less than said predetermined cutoff value to derive an aliased color value;
offset means for modifying the dither noise value when the color value is greater than said predetermined cutoff value to derive a modified dither noise value;
adder means for generating a dithered color value, said adder means for mathematically combining said dither noise value with said aliased color value and for mathematically combining said modified dither noise value with said color value;
clamping means for insuring that said dithered color value resides within a predetermined color range; and
quantizing means for quantizing said dithered color value to derive a dithered and quantized color value for storage in memory.
3 Assignments
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Accused Products
Abstract
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.
40 Citations
16 Claims
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1. A system for dithering and quantizing image data, comprising:
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dithering means for providing a dither noise value; comparator means for comparing a color value corresponding with the image data with a predetermined cutoff value; aliasing means for aliasing the color value with other color values below said predetermined cutoff value when the color value is less than said predetermined cutoff value to derive an aliased color value; offset means for modifying the dither noise value when the color value is greater than said predetermined cutoff value to derive a modified dither noise value; adder means for generating a dithered color value, said adder means for mathematically combining said dither noise value with said aliased color value and for mathematically combining said modified dither noise value with said color value; clamping means for insuring that said dithered color value resides within a predetermined color range; and quantizing means for quantizing said dithered color value to derive a dithered and quantized color value for storage in memory. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for dithering and quantizing image data, comprising the steps of:
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generating dither noise; comparing a color value with a predetermined cutoff value; when the color value is greater than said predetermined cutoff value, modifying said dither noise to derive modified color noise; when the color value is less than said predetermined cutoff value, aliasing the color value with other color values below said predetermined cutoff value to derive an aliased color value; when the color value is greater than said predetermined cutoff value, mathematically combining said modified dither noise with said color value to derive a dithered color value; when the color value is less than said predetermined cutoff value, mathematically combining said dither noise with said aliased color value to derive said dithered color value; clamping said dithered color value to insure that said dithered color value resides within a predetermined color range; and quantizing said dithered color value to derive a dithered and quantized color value for storage in memory. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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Specification