Data compression for palettized video images
AssigneeRicoh Company, Ltd.
InventorsMichael J. Gormish, Martin P. Boliek
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Abstract
A data compression system uses sameness information, such as temporal sameness of corresponding pixels, in the coding process. Two sets of contexts are used, one set when a pixel is the same as a sameness pixel, and one set of contexts for residual coding of the pixel when it is not the same. The use of the sameness bit saves computation because, if in decoding the one "sameness" bit, a decompressor determines that the pixel is equal to the corresponding pixel in a previous frame, then no further decoding is needed for that pixel.
Claims23
A method of compressing an input symbol of a plurality of input symbols comprising the steps of:
- comparing the input symbol to a sameness symbol, where the sameness symbol is a symbol relative to the input symbol according to a sameness relation, the step of comparing resulting in a sameness result;
- determining a sameness context for the input symbol, where the sameness context is dependent on at least one context symbol, or portions thereof, relative to the input symbol according to a sameness context model;
- outputting the sameness result and the sameness context to an entropy coder;
- if the sameness result is negative, indicating a nonequivalence of the input symbol and the sameness symbol, performing the steps of:
- determining a residual context for the input symbol, where the residual context is defined at least by context symbols, or portions thereof, relative to the input symbol according to a residual context model;
- and
- outputting a representation of the input symbol as a residual result and the residual context to a coder;
- and
- coding the sameness result, and the residual result if output, using the coder.
A context modeller, for use in a compression or decompression system, wherein pixels are input and result values and context values are output to an entropy coder, the context modeller comprising:
- an input pixel register, coupled to receive a pixel in each of a plurality of clock cycles including a current clock cycle in which the input pixel register stores a current pixel value, the input pixel register clocked by a pixel clock;
- a frame store, coupled to the input pixel register for storing previous contents of the input pixel register, including an output for context data;
- a comparator coupled to the frame store and the input pixel register, which comparator compares a first portion of the context data to the current pixel value, and outputs at least one sameness indication including a primary sameness indication;
- a context register, coupled to at least to the comparator, which stores at least the primary sameness indication and a second portion of the context data;
- result output means, coupled to the input pixel register, for outputting a result value based on the current pixel value;
- a sameness mask, coupled to the context register, which masks bits from contents of the context register to form a sameness context value;
- a residual mask, coupled to the context register, which masks bits from contents of the context register to form a residual context value;
- and
- control logic means for outputting the sameness context value as the context value corresponding to the result value output by the result output means when the primary sameness indication indicates a sameness and for outputting the residual context value as the context value corresponding to the result value output by the result output means when the primary sameness indication indicates other than a sameness.
Dependencies are inferred from the claim text.