K-means Clustering for Multispectral Images Using Floating-Point Divide

Many signal processing algorithms can be accelerated using reconfigurable hardware. To achieve a good speedup compared to running software on a general purpose processor, fine-grained control over the bitwidth of each component in the datapath is desired. This goal can be achieved by using NU´s variable precision floating-point library. To analyze the usefulness of the floating-point divide unit, we incorporate it into our previous implementation of the Kmeans clustering algorithm applied to multispectral satellite images. With the lack of a floating-point divide hardware implementation, the mean updating step in each iteration of the K-means algorithm had to be moved to the host computer for calculation. The new means calculated on the host then had to be moved back to the FPGA board for the next iteration of the algorithm. This added data transfer overhead between the host and the FPGA board. In this work, we use the new fp div module to implement the mean updating step in FPGA hardware. This greatly reduces the communication overhead between host and FPGA board and further accelerates run time. The Kmeans clustering example illustrates the use of the fp div, fix2float and float2fix modules seamlessly assembled together in a real application. It is the first implementation that has the complete K-means computation done in FPGA hardware. Our results show that the hardware implementation achieves a speedup of over 2150x for core computation time and about 11x for total run time including data transfer time. They also show that the divide in FPGA hardware is 100 times faster than in software. Moreover, implementing divide in the FPGA frees the host to work on other tasks concurrently with K-means clustering, thus providing further speedup by allowing the image analyst to exploit this coarse grained parallelism.