LOSSLESS COMPRESSION OF COLOR IMAGE DATA USING ENTROPY ENCODING

摘要

A method of compressing a digital continuous tone image of pixels situated on scan lines, each pixel having a pixel value defined by at least one color channel value, a color channel value having B bits of precision (B 1), the method producing compressed image data and comprising, for a current pixel to be encoded, said current pixel having an actual pixel value, predicting a predicted pixel value based on pixel values of at least one previously processed pixel from the same image, using a fixed rule, determining a difference parameter based on a difference value of said predicted pixel value and the actual pixel value of said current pixel to be encoded, and inspecting the difference parameter for existence of an uninterrupted series of highest order bits having a value equal to zero, removing at least part of said highest order zero bits, and, if a number of bits within predetermined limits remains, generating a compression code having a predetermined fixed length, said code indicating the number of remaining bits. Several pre-processing steps of the image data are disclosed for preparing the image data in a way that they can be compressed more effectively in the actual compression process.