Some experiments in adaptive and predictive hadamard transform coding of pictures

This paper describes some experiments in adaptive and predictive Hadamard transform coding of still pictures using a small transform block (2 × 2 × 2). Predictive coding of the transform coefficients is discussed using certain combinations of coefficients of the present as well as previously transmitted blocks as predictors. Two separate adaptive quantization techniques are considered. The first technique relates to pcm quantization, in which a uniform pcm quantizer with a different number of quantization levels is used, depending upon the spatial activity within the block. The second technique alters the quantizer of a predictive transform coder based on a weighted sum of already transmitted coefficients of the present and previous blocks. Finally, we give a comparison of three coding techniques: (i) adaptive predictive transform coding, (ii) nonadaptive transform coding, and for comparison, (iii) nonadaptive predictive coding in the picture element domain using a two-dimensional prediction.