Patent attributes
In an image encoder (1), a quantizer (11) makes a quantization-step size set for each of low-frequency subbands whose resolution level belongs to a predetermined resolution level coincide with a quantization-step size set for each subband to encode an original image having the resolution level as it is. A low-pass rate controller (17) provides a rate control for the bit rate of arithmetic code D16 in all code blocks in a low-frequency subband to be less than a predetermined target bit rate. A high-pass rate controller (18) provides such a rate control that the bit rate of arithmetic code D17 in all code blocks in other subbands than the low-frequency subbands will be less than a target bit rate, that is, a bit rate resulted from subtraction of a bit rate D18 having actually occurred in the low-frequency subbands from a final target bit rate.
