An image processing device comprising: a decoding unit configured to decode encoded data including an initial difference coefficient that is a difference between a DC coefficient and a predetermined initial value, a replacement difference coefficient that is a difference between the DC coefficient and a (0, 0) coefficient located at the beginning of an 8x8 quantization matrix whose size is limited to be not greater than a transmission size that is the maximum size allowed in transmission, and further difference coefficients each being a difference between two adjacent coefficients in a sequence of coefficients of the 8x8 quantization matrix arranged in scan order and to set, in case a current quantization matrix is copied and a difference value between a value of identification information identifying a reference quantization matrix and a value of identification information identifying the current quantization matrix is equal to 0, a 16x16 default quantization matrix as the current quantization matrix and to set, in case the current quantization matrix is not copied, a 16x16 quantization matrix as the current quantization matrix; an inverse DPCM unit configured to set DC coefficient by adding the initial value to the initial difference coefficient and to set the 8x8 quantization matrix by setting the (0, 0) coefficient located at the beginning of the 8x8 quantization matrix by adding the DC coefficient to the replacement difference coefficient and by setting the remaining coefficients of the 8x8 quantization matrix by stepwise adding the further difference coefficients to the (0, 0) coefficient, wherein a remaining coefficient at a particular position in scan order is the sum of the (0, 0) coefficient and the difference coefficient up to said particular position; a matrix size transformation unit configured to upconvert the 8x8 quantization matrix into the 16x16 quantization matrix by performing a nearest neighbor interpolation process on matrix elements of the 8x8 quantization matrix; a replacement unit configured to replace a (0, 0) coefficient located at the beginning of the 16x16 quantization matrix set by the matrix size transformation unit with the DC coefficient set by the inverse DPCM unit; and a dequantization unit configured to dequantize quantized data obtained by decoding encoded data, using the 16x16 quantization matrix in which the (0, 0) coefficient located at the beginning has been replaced with the DC coefficient by the replacement unit or the 16x16 default quantization matrix. a decoding unit configured to decode encoded data including an initial difference coefficient that is a difference between a DC coefficient and a predetermined initial value, a replacement difference coefficient that is a difference between the DC coefficient and a (0, 0) coefficient located at the beginning of an 8x8 quantization matrix whose size is limited to be not greater than a transmission size that is the maximum size allowed in transmission, and further difference coefficients each being a difference between two adjacent coefficients in a sequence of coefficients of the 8x8 quantization matrix arranged in scan order and to set, in case a current quantization matrix is copied and a difference value between a value of identification information identifying a reference quantization matrix and a value of identification information identifying the current quantization matrix is equal to 0, a 16x16 default quantization matrix as the current quantization matrix and to set, in case the current quantization matrix is not copied, a 16x16 quantization matrix as the current quantization matrix; an inverse DPCM unit configured to set DC coefficient by adding the initial value to the initial difference coefficient and to set the 8x8 quantization matrix by setting the (0, 0) coefficient located at the beginning of the 8x8 quantization matrix by adding the DC coefficient to the replacement difference coefficient and by setting the remaining coefficients of the 8x8 quantization matrix by stepwise adding the further difference coefficients to the (0, 0) coefficient, wherein a remaining coefficient at a particular position in scan order is the sum of the (0, 0) coefficient and the difference coefficient up to said particular position; a matrix size transformation unit configured to upconvert the 8x8 quantization matrix into the 16x16 quantization matrix by performing a nearest neighbor interpolation process on matrix elements of the 8x8 quantization matrix; a replacement unit configured to replace a (0, 0) coefficient located at the beginning of the 16x16 quantization matrix set by the matrix size transformation unit with the DC coefficient set by the inverse DPCM unit; and a dequantization unit configured to dequantize quantized data obtained by decoding encoded data, using the 16x16 quantization matrix in which the (0, 0) coefficient located at the beginning has been replaced with the DC coefficient by the replacement unit or the 16x16 default quantization matrix.