A decoding apparatus for decoding a bitstream comprising an encoded image signal that corresponds to an input image signal, said input image signal including a colour difference signal and being in the 4:2:2 format and in the YCbCr colour space, the apparatus comprising: decoding means for decoding the encoded image signal to generate quantized transform coefficients; an inverse quantizing part adapted to perform inverse-quantization of the quantized transform coefficients decoded by the decoding means to generate 2x4 DC chroma blocks of transform coefficients constituted by collecting only the chroma DC coefficients of 4x4 transform coefficient blocks within 8x16 pixel blocks with 8x8 pixel blocks lined up in a vertical direction and to perform inverse-quantization of the AC coefficients of said 4x4 transform coefficient blocks; an inverse transform part that is adapted to act on the transform coefficients inversely quantized by the inverse quantizing part by performing an inverse Hadamard transform in 2x4 block units on the 2x4 DC chroma blocks, and performing a further inverse integer transform, with the inversely Hadamard transformed 2x4 DC chroma block coefficients as the DC coefficients of each of the eight 4x4 blocks corresponding to the 8x16 pixel blocks; and an intra-image prediction part for generating a prediction image by performing intra-image predictive decoding using an output signal from the inverse transform part, the prediction image including a prediction colour difference signal composed in 8x16 pixel block units; wherein the inverse quantizing part is adapted to use a scale in inverse quantization whose value corresponds to a scale in quantization used in quantizing the quantized transform coefficients, wherein: when a QPc parameter for determining a quantized chroma DC coefficient is T or more, an inverse quantized DC chroma coefficient, fdc", corresponding to a quantized chroma DC coefficient, fdc', of a 2 x 4 DC chroma block is represented by the equation fdc’’ i j = fdc’ i j × Q QP c % 6, 0, 0 < < QPc / 6 − 2 i = 0... 1, j = 0... 3 and when a QPc parameter for determining a quantized chroma DC coefficient is less than T, an inverse quantized DC chroma coefficient, fdc", corresponding to a quantized chroma DC coefficient, fdc', of a 2 x 4 DC chroma block is represented by the equation fdc’’ i j = fdc’ i j × Q QP c % 6, 0, 0 < < 2 − QPc / 6 i = 0... 1, j = 0... 3 characterized in that T=6. decoding means for decoding the encoded image signal to generate quantized transform coefficients; an inverse quantizing part adapted to perform inverse-quantization of the quantized transform coefficients decoded by the decoding means to generate 2x4 DC chroma blocks of transform coefficients constituted by collecting only the chroma DC coefficients of 4x4 transform coefficient blocks within 8x16 pixel blocks with 8x8 pixel blocks lined up in a vertical direction and to perform inverse-quantization of the AC coefficients of said 4x4 transform coefficient blocks; an inverse transform part that is adapted to act on the transform coefficients inversely quantized by the inverse quantizing part by performing an inverse Hadamard transform in 2x4 block units on the 2x4 DC chroma blocks, and performing a further inverse integer transform, with the inversely Hadamard transformed 2x4 DC chroma block coefficients as the DC coefficients of each of the eight 4x4 blocks corresponding to the 8x16 pixel blocks; and an intra-image prediction part for generating a prediction image by performing intra-image predictive decoding using an output signal from the inverse transform part, the prediction image including a prediction colour difference signal composed in 8x16 pixel block units; wherein the inverse quantizing part is adapted to use a scale in inverse quantization whose value corresponds to a scale in quantization used in quantizing the quantized transform coefficients, wherein: when a QPc parameter for determining a quantized chroma DC coefficient is T or more, an inverse quantized DC chroma coefficient, fdc", corresponding to a quantized chroma DC coefficient, fdc', of a 2 x 4 DC chroma block is represented by the equation fdc’’ i j = fdc’ i j × Q QP c % 6, 0, 0 < < QPc / 6 − 2 i = 0... 1, j = 0... 3 and when a QPc parameter for determining a quantized chroma DC coefficient is less than T, an inverse quantized DC chroma coefficient, fdc", corresponding to a quantized chroma DC coefficient, fdc', of a 2 x 4 DC chroma block is represented by the equation fdc’’ i j = fdc’ i j × Q QP c % 6, 0, 0 < < 2 − QPc / 6 i = 0... 1, j = 0... 3