Method and apparatus for compressing and decompressing data

摘要

Methods and apparatus are provided for compressing and decompressing image data by producing two sets of reduced size image data, generating a modulation value for each elementary of the area from the image data, the modulation value encoding information about how to combine the sets of reduced size image data to generate an approximation to the image. In one arrangement, a set of index values is generated corresponding to a set of modulation values for each of the respective elementary areas of a group of elementary areas and these are assigned to each respective group and a second set of index values corresponding to one of the set of first index values for each elementary areas is assigned to each first group of elementary areas. These index values are stored for use in deriving modulation data more accurately when decompressing the image data.

主权项

1. A method for compressing blocks of electronic image data, each block comprising a plurality of elements of the electronic image data, the method comprising the steps of:
generating a modulation value for each of said plurality of elements of image data; generating at least two sets of reduced size image data from the electronic image data, each element of each set of reduced size image data being representative of a plurality of elements of the electronic image data, wherein the sets of reduced size image data can be combined using the modulation values to provide a representation of the electronic image data; for each of the blocks:
for each of a plurality of groups of modulation values generated for elements of the image data in the block, assigning a set of bits of modulation data, wherein the set of bits of modulation data assigned to encode a group of modulation values comprises:
(i) a plurality of modulation indicators for a respective plurality of modulation values in the group, wherein the modulation indicator for a respective modulation value in the group indicates which of a set of one or more candidate modulation values is to be used to represent that modulation value in the group; and(ii) a plurality of modulation value choice bits indicating the set of one or more candidate modulation values for the group; and storing the sets of reduced size image data, and the sets of bits of modulation data for the groups of modulation values for each of the blocks of elements of the electronic image data.