A new regional projection transformation (RPT) to recognize unconnected patterns and patterns with isolated noise is presented. This new approach simplifies the process of recognizing compound patterns by transforming them into an integral object. Two kinds of RPT transforms are described and analysed: (1) diagonal-diagonal regional projection transformation (DDRPT), and (2) horizontal-vertical regional projection transformation (HVRPT). The patterns transformed by these two methods have several important properties which can simplify contour processing. The essential parallelisms in DDRPT and HVRPT can also facilitate their parallel implementation and parallel algorithms for both DDRPT and HVRPT, and their VLSI implementation are also designed. They can speed up the recognition process considerably with a time complexity of O(N) for processing a pattern with size of N × N, compared with O(N) using a uniprocessor. © 1993.