Compression apparatus with arithmetic coding using a contextual models, which leads to variable pattern lengths in binary image data is adaptive

摘要

The present invention provides a method for compressing image data. The method first detects a pattern in a first subset of the image data, where the second subset being collocated to a second subset. If no pattern is detected, then a text mode context model is selected. If a pattern is detected, then the period of the pattern is detected and a pattern mode context model is selected. The pattern mode context model has a width directly related to the period of the pattern detected. An arithmetic compressor compresses the second subset using the selected context model.