Television transmission system using transform coding

Abstract

A television transmission system for digital picture signals in which each picture is split up into sub-pictures of NxN pixels for the purpose of reducing the bit rate. Each sub-picture is subjected to a two-dimensional discrete cosine transform (DCT) for determining basic picture weighting factors (coefficients) which are converted by adaptive coding into code words of variable length. This two-dimensional DCT is realized by multiplying the pixels of each row of the sub-picture by the NxN DCT matrix (one-dimensional transform). Consequently, an NxN array of product elements is obtained. The transposed version thereof is once more multiplied by the NxN DCT matrix. Such a one-dimensional transform includes three main steps. In a first main step, the pixels of a row are converted in a first iteration step, into N/2 sum elements u.sub.1,i and N/2 difference elements v.sub.1,i. In a subsequent iteration step, the N/2 sum elements u.sub.1,i are converted into N/4 further sum elements u.sub.2,i and N/4 further difference elements v.sub.2,i. This process is repeated until only two sum elements are left. The difference elements obtained in each step are used to determine a plurality of auxiliary sum elements in still further iteration steps. The remaining two sum elements, the difference elements and the auxiliary sum elements are each multiplied in the second main step by an associated linear combination of elements of the DCT matrix. Of the sub-products thus obtained, selected one's of those products are added together or are subtracted from each other in the third main step so that the desired product elements are obtained.