VARIABLE RATE ENCODING DEVICE FOR IMAGE

摘要

PROBLEM TO BE SOLVED: To control variation in the size of quantization steps so as to reduce it as small as possible, to suppress variation in picture quality and to transmit always stable encoded images without generating useless information. SOLUTION: A maximum allowable information operation circuit 12 for calculating maximum allowable information to be allowed for a succeeding image frame by using the free capacity of a buffer for storing images encoded by an image encoder 100 and an average encoding quantity and maximum encoding quantity respectively obtained by transmitting information at an average rate and a peak rate is prepared. An information quantity comparator 10 compares quantity obtained by adding weight corresponding to the sort of a picture to the maximum allowable information quantity with information quantity obtained by encoding a current image frame. An quantization step size control circuit 9 determines the quantization step size of the succeeding image frame based on the compared result. Consequently each image can be quantized by an optimum quantization step size always considering the current information quantity.