1. An image processing system comprising an image processing apparatus and an image output apparatus, said image processing apparatus comprising: first input means for inputting encoded image data encoded using first entropy coding; first decoding means for obtaining transform coefficients or quantization values of the transform coefficients by decoding said encoded image data; encoding means for generating encoded data by encoding the transform coefficients or the quantization values of the transform coefficients obtained by said first decoding means using second entropy coding different from the first entropy coding, and generating a code sequence containing the encoded data; and output means for outputting the code sequence generated by said encoding means to said image output apparatus, and said image output apparatus comprising: second input means for inputting the code sequence output from said output means; second decoding means for entropy-decoding the encoded data contained in the code sequence to obtain the transform coefficients or the quantization values of the transform coefficients; and image reconstruction means for reconstructing an image on the basis of the transform coefficients or the quantization values of the transform coefficients.