IMAGE ENCODER AND IMAGE DECODER

摘要

PURPOSE:To prevent the degradation of the image quality of an important part and to suppress the degradation of picture quality due to the loss of information by detecting an important image area and correcting an orthogonal transformation coefficient based upon a quantizing error corresponding to the detected area. CONSTITUTION:An orthogonal transformation part 15 performs orthogonal transformation a predictive error signal obtained by calculating a difference between a predictive value read out from a frame memory 20 and an input image signal by a subtraction part 14 to find out an orthogonal transformation coefficient. A quantizing part 16 quantizes the coefficient by means of a prescribed quantizing level and compressed information. At this time, an important image area in the input image signal is detected by an area detecting part 10 and a quantizing error between the area and the orthogonal transformation coefficient corresponding to the area is calculated by an error coding control part 12. An error quantizing part 11 quantizes the obtained error and adds the quantized error to a reverse quantizing means to correct the quantized error and restore an image. Consequently an image reducing quantized error in an important image area can be obtained.