An discrete cosine transform (DCT) apparatus is adaptive so as to choose between alternative transform modes for each successive pixel block to be transformed and subsequently variable-length-coded. A first transform device performs a DCT on a subject pixel block. A second transform device performs a DCT on the same subject pixel block of data which has been processed such that the frequency domain transformed data is distributed in a lower frequency compared with the transform coefficients produced by the first transform device. A pair of scanners scan the respective transform coefficients output by the transform devices according to predetermined patterns. A set of four counters accumulate information about the transform coefficients, as scanned by the scanners, so as to indicate the amount of data which would be produced by the respective sets of transform coefficients when variable-length-coded. Based upon the counts produced by the counters, a prediction is made as to which transform mode will produce the least amount of variable-length-code, and the corresponding transform coefficients are selected to be sent to the variable-length-coder.
Adaptive orthogonal transform coding apparatus