Data compression for indexed color image data

A parallel context modeller which provides context information for pixels in an image to either an entropy coder or an entropy decoder, comprising:

• a plurality of memory banks, each memory bank comprising storage for a plurality of pixels and context pixels for that plurality of pixels;
• a plurality of context modellers, each linkable to one of the plurality of memory banks and each memory bank linkable to one of the plurality of context modellers, each of the plurality of context modellers including a pause input for pausing the context modeller;
• and
• a context modeller controller, which includes:
• an image input for pixels of an image;
• a memory bus for loading the pixels into memory banks of the plurality of memory banks;
• a plurality of routing signal lines for controlling a specific coupling of memory banks to context modellers;
• and
• outputs to pause context modellers.

A parallel entropy coder, comprising:

• an image storage memory for storing pixel values collectively representing an image to be compressed;
• a coder controller, coupled to the image storage memory to read pixel values therefrom;
• a plurality of context modellers, each coupled to the coder controller to receive pixel values for context pixels and a current pixel, wherein each context modeller provides an output of a result and a context for the result, the result being the outcome of a test of the current pixel against a color plane value associated with the context modeller outputting the result, and the context being comparisons of the context pixels with the color plane value,
• wherein the coder controller controls the progression of each of the plurality of context modellers over the image to ensure that no context modeller uses for context a pixel which has not already been at least partially coded.

A parallel entropy decoder, comprising:

• an image storage memory for storing decoded pixel values in pixel locations, the pixel values in the pixel locations collectively representing an image;
• a decoder controller, coupled to the image storage memory to read pixel values therefrom and to write pixel values thereto;
• a plurality of context modellers, each coupled to the coder controller to receive context pixel values, wherein each context modeller provides a context output, the context output indicating the context of a current pixel being decoded, and the context being a set of comparisons of the context pixels with a current color plane value;
• a plurality of coders, each coupled to a context modeller of the plurality of context modellers, wherein each coder uses a context for a current color plane to decode a bit indicating whether or not the current pixel being decoded is in the current color plane;
• and
• means for communicating the bit to the coder controller.