Implementation of a parallel and pipelined watershed algorithm on FPGA

This paper describes an implementation of a parallel and pipelined watershed algorithm on FPGA. In the algorithm, pixels in a given image are repeatedly scanned from top-left to bottom-right, and then from bottom-right to top-left. Because of these simplified memory accesses, N pixels in a given image can be processed in parallel by reading N lines at the same time. However, N is limited by the number of external memory banks that store image data. In our implementation, in order to achieve high performance using an FPGA with limited number of external memory banks, (1) a given image is divided to K regions, (2) several of them are cached on the FPGA, (3) the watershed algorithm is applied on those regions, and (4) the next (or previous) region is loaded to the FPGA during the computation to hide the loading time. In our current implementation on XC2V6000, up to 32 pixels can be processed in parallel. The performance for 512 x 512 pixel images is about 3 - 4 msec, which is fast enough for real-time applications.