Data compression method having a fixed ratio of compression for image data, and image data compression device

摘要

A data compression method and device for an image processor such as a digital copying machine. The picture image information is divided into blocks and the blocks are characterized by the variation in density level found within each block. The individual blocks are then encoded. During encoding, the allocation of the chromatic gradation information and the resolution information are varied in accordance with the characteristics of the particular block. The amount of chromatic gradation information and the amount of resolution information are inversely proportional to each other. Because gradation information and the resolution information are varied, the total amount of information in each encoded block is constant. Therefore, the data compression is tailored to the individual requirements of each image block, but the total amount of information in each compressed block is constant. Because the data compression ratio is constant, storage and processing needs for the compressed information can be accurately and easily predicted before the data is compressed.