IMAGE COMPRESSION DECODER FOR SELECTING FREQUENCY DISTRIBUTION DEPENDING ON DEGREE OF DISPERSION IN GRADATION VALUE AROUND CODING PIXEL

摘要

PROBLEM TO BE SOLVED: To prevent a coding information amount from being undesirably increased by storing frequency information of a prediction difference for each dispersion in a surrounding gradation value and using the frequency information by each variance and coding an image. SOLUTION: The decoder is provided with a frequency distribution table group 12 consisting of 9 frequency distribution tables consisting of 511 size elements corresponding to 511 ways from, e.g. -255 to +255 resulting from integers-processed from prediction differences. An index of dispersion is selected from an integers among 0 to 8. The decoder is also provided with a frequency distribution table selection device 10 that selects one frequency distribution table among the frequency distribution table group 12 and a prediction difference is subject to entropy coding by the frequency distribution table. Waste of the coding information amount due to unification of different distributions in a conventional method is avoided by using each frequency distribution table based on the index of dispersion.