Patent ID: 7463780

Claim:
An image decoder comprising: inverse format means which decomposes the encoded code stream into at least an arithmetic code and a predetermined parameter, the encoded code stream having been generated by hierarchically performing a filtering process on an input image to generate a plurality of sub-bands, quantizing, with a quantization means, coefficients in each sub-band, dividing the sub-bands, to generate a plurality of code blocks each having a predetermined size, generating, for each code block, bit planes from a most significant bit to a least significant bit, generating the arithmetic code by arithmetically encoding a coding pass generated for each bit plane; and adding, with a format means, a header to the arithmetic code to generate an encoded code stream, wherein the quantization means sets, in response only to a selected image quality level, a corresponding width of a dead zone, the dead zone being a quantization zone where the coefficients are quantized to a value of 0, and the format means sets the predetermined parameter included in the header; decoding means which decodes the arithmetic code; encoded-pass decoding means which reconstructs the bit planes from the most significant bit to the least significant bit by decoding the encoded coding pass for each bit plane; code block reconstruction means which reconstructs the code blocks, based on the bit planes from the most significant bit to the least significant bit; sub-band generation means which collects the code blocks to generate the sub-bands; inverse quantization means which inversely quantizes a plurality of quantization coefficients for each sub-band, with use of the predetermined parameter; and filtering means which hierarchically performs a filtering process on the sub-bands, to reconstruct the input image, wherein the inverse quantization means adds the predetermined parameter to each of the quantization coefficients for every one of the sub-bands, and multiplies each of the addition results thereof by a quantization step size, to inversely quantize the quantization coefficients for each sub-band.