IMAGE COMPRESSION PROCESSING UNIT AND ITS METHOD, AND DIGITAL CAMERA USIGN THE UNIT

摘要

PROBLEM TO BE SOLVED: To prevent image quality deterioration even at a high compression rate by updating compression parameters for each spatial frequency based on a calculation result of a space frequency distribution in an image so as to attain quantization corresponding to the characteristic of an image compression. SOLUTION: An analog image signal received from an input port 1 is converted into a digital signal by an image A/D converter 2 and an image signal processing circuit 3 applies a general gamma correction processing and a processing such as contour emphasis to the digital signal. A high frequency extraction circuit 6 detects a high frequency component with a high spatial frequency from the signal processed by the image signal processing circuit 3 and gives information to a compression control circuit 5. The compression control circuit 5 adjusts a quantization accuracy to keep a code amount rate within a prescribed range to compress the data so that a buffer in an image compression coder is not saturated. In the case of adjusting the code amount rate, not only a Q scale but also a Q table are changed. Thus, quantization accuracy is changed corresponding to an optical spatial frequency.