IMAGE ENCODING DEVICE, ITS METHOD, PROGRAM, AND RECORDING MEDIUM RECORDING THE PROGRAM

摘要

PROBLEM TO BE SOLVED: To execute encoding of high compression efficiency by using a dictionary table registering a symbol corresponding to the pattern of a unit to be an encoding unit by constituting image data having periodicity of units each of which consists of pixels in one period. SOLUTION: An image encoding device has a dither processing part 10, a unit preparation part 11, a dictionary retrieving part 12 and a variable length encoder 13. The unit preparation part 11 constitutes dither-processed image data of units each of which consists of pixels in one period and the unit is used as an encoding unit. The dictionary retrieving part 12 has a dictionary table registering symbols corresponding to the patterns of units, compares the pattern of a certain unit with the symbols registered in the table and when a symbol corresponding to the pattern is not registered as the result of comparison, extracts the symbol concerned and moves the symbol to the top of the table to update the dictionary. The variable length encoder 13 allocates short codes to the indexes of symbols successively from the index of a head symbol to encode the image data.