Image data compression is achieved through the use of a two-dimensional (2-D) transform operation on the gray-level pixels within an image subsection followed by 2-D DPCM encoding of common transform coefficients from disjoint image subsections. Earlier results for this 2-D hybrid scheme employing the Discrete Cosine Transform (DCT) indicate an overall improvement in image source coding gain vis-a-vis conventional 2-D transform coding. Hybrid system performance dependence on transform block size is demonstrated along with the rank-ordering of the relative performance obtained when using the Haar, Walsh, Slant and DCT 2-D orthogonal transforms. It is shown that performance gains over conventional block 2-D transform coding are realized for transforms which are less efficient than the DCT. This hybrid system will provide a means of substantially improving existing hardware transform coding systems with a minimal increase in hardware complexity.