IMAGE CODER, IMAGE CODING METHOD, AND IMAGE DECODER AND IMAGE DECODING METHOD

PROBLEM TO BE SOLVED: To provide an image coder and an image coding method for reducing mosquito noise. SOLUTION: A DCT circuit 131 applies discrete cosine transform to input image data i(n1 ,n2 ) divided into blocks by each block to obtain coefficient data X(m1 ,m2 ) and a quantization circuit 132 applies quantization arithmetic operation to the coefficient data X(m1 ,m2 ) to obtain coefficient data Xq (m1 ,m2 ). Further, a correlation discrimination circuit 134 discriminates correlation between each block of the input image data and a reference pattern stored in a pattern memory 133. A correction data attaching section 138 attaches correction data CD to correct a high frequency component of the coefficient data to the quantized Xq (m1 ,m2 ) of each block corresponding to the block discriminated to have correlation, and an encoding circuit 139 applies Huffman coding to the data after the correction to obtain encoded data. The correction data CD are generated from difference data Xsub (m1 ,m2 ) between the coefficient data X(m1 ,m2 ) and Xdq (m1 ,m2 ) obtained resulting from applying inverse quantization to the Xq (m1 ,m2 ) at an inverse quantization circuit 135.