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 4:4:4 format and in a colour space selected from YCbCr, RGB and XYZ, the apparatus comprising: decoding means for decoding the encoded image signal to generate quantized transform coefficients; an inverse quantization means adapted to perform inverse quantization of the quantized transform coefficients decoded by the decoding means to generate 4x4 DC chroma blocks of transform coefficients constituted by collecting only the chroma DC coefficients of 4x4 transform coefficient blocks within 16x16 pixel blocks and to perform inverse quantisation of the AC coefficients of said 4x4 transform coefficient blocks; an inverse transform means adapted to act on the transform coefficients inversely quantized by the inverse quantization means by performing an inverse Hadamard transform in 4x4 block units on the 4x4 DC chroma blocks, and performing a further inverse integer transform in 4x4 block units with the inversely Hadamard transformed 4x4 DC chroma block coefficients as the DC coefficients of each of the sixteen 4x4 blocks corresponding to the 16x16 pixel blocks; and an intra-image prediction part for generating a prediction image using an output signal from the inverse transform means, the prediction image including a prediction colour difference signal composed in 16x16 pixel block units; characterized in that when a QPc parameter for determining a quantized chroma DC coefficient is 6 or more, an inverse quantized DC chroma coefficient, fdc", corresponding to a quantized chroma DC coefficient, fdc', of a 4 x 4 DC chroma block is represented by the equation fdc’’ i j = fdc’ i j × Q QPc % 6, 0, 0 < < QPc / 6 − 2 i, j = 0..3 and when a QPc parameter for determining a quantized chroma DC coefficient is less than 6, an inverse quantized DC chroma coefficient, fdc", corresponding to a quantized chroma DC coefficient, fdc', of a 4 x 4 DC chroma block is represented by the equation fdc’’ i j = fdc’ i j × Q QPc % 6, 0, 0 > > 2 − QPc / 6 i, j = 0..3. decoding means for decoding the encoded image signal to generate quantized transform coefficients; an inverse quantization means adapted to perform inverse quantization of the quantized transform coefficients decoded by the decoding means to generate 4x4 DC chroma blocks of transform coefficients constituted by collecting only the chroma DC coefficients of 4x4 transform coefficient blocks within 16x16 pixel blocks and to perform inverse quantisation of the AC coefficients of said 4x4 transform coefficient blocks; an inverse transform means adapted to act on the transform coefficients inversely quantized by the inverse quantization means by performing an inverse Hadamard transform in 4x4 block units on the 4x4 DC chroma blocks, and performing a further inverse integer transform in 4x4 block units with the inversely Hadamard transformed 4x4 DC chroma block coefficients as the DC coefficients of each of the sixteen 4x4 blocks corresponding to the 16x16 pixel blocks; and an intra-image prediction part for generating a prediction image using an output signal from the inverse transform means, the prediction image including a prediction colour difference signal composed in 16x16 pixel block units;