Block classification image coding with combined transforms

Methods of employing a combination of two recently reported simple transforms (High Correlation Transform and Low Correlation Transform) using block adaptive transform coding with spatial domain activity classification are examined. It is found that for small block size, (viz. 8×8), increased coding efficiency can be had by employing a combination of the two new transforms, particularly for high activity images. The performance of such systems for small block size is found to be close, and sometimes superior, to that of a more conventional block classification adaptive transform coder employing the more complex real number cosine transform.