The invention relates to an image coding/decoding method and to a recording medium on which a program for this method has been recorded, and the object thereof is to raise the compression rate of image data while the image data is maintained at a high quality. In FIG. 1(A), image data is divided into a plurality of pixel blocks, a DC image comprising mean values of respective ones of the blocks is generated, a corresponding block mean value is separated from each pixel block and a residual vector is obtained for every block. In a case where the magnitude of the residual vector is equal to or greater than an allowable value, orthogonal bases for approximating the residual vector by an adaptive orthogonal transformation that employs a nest of the DC image is obtained and coded. In FIG. 1(B), in a case where the residual vector is less than the allowable value, pixel data of 4×4 pixels of a local block S is reproduced directly on the decoding side by a direct method of AC component prediction, instead of coding the orthogonal base, based upon five items of DC image data of upper, bottom, left, right blocks U, B, L, R inclusive of a local block S comprising a block mean value of 4×4 pixels.