IMAGE COMPRESSION DEVICE, COMPRESSING METHOD, STORAGE MEDIUM, IMAGE DECOMPRESSION DEVICE, DECOMPRESSING METHOD, AND STORAGE MEDIUM

摘要

An image compression device having a prediction unit for predicting a value of a compressing target pixel from peripheral values, and quantizing prediction error between a prediction value of the prediction unit and a value of an actual pixel in a predetermined quantizing step, comprising: a specific pixel level difference evaluation unit sequentially calculating the difference value between the level values as a sum of the prediction values corresponding to each of the compressed pixel immediately before the compressing target pixel and peripheral compressed pixels adjacent to the pixel and the quantization value of the prediction error, and evaluating the sameness of the difference value; and a quantization switching unit controlling the quantization in the quantizing step more precise than the quantizing step used when the difference value continuously indicates the same value as a result of the evaluation by the specific pixel level difference evaluation unit.