Image data is decomposed into subbands and quantized by a discrete wavelet transformer (102) and coefficient quantizer (103). On the other hand, a high-resolution region information input unit (105) inputs region designation information H(x, y) that designates a region which requires a high resolution, and a mask generator (106) obtains, based on H(x, y), mask information M(S, x, y) indicating if coefficients of HL2, LH2, and HH2 are generated with reference to pixels of the high-resolution region. A coefficient correction unit (104) corrects the quantized coefficients of respective subbands with reference to M(S, x, y) if subband S is one of HL2, LH2, and HH2, and does not correct if subband S is other than HL2, LH2, and HH2.