Real-time processing of local contrast enhancement on FPGA

Local contrast enhancement is a technique to enhance the visibility of local details of an image by increasing the contrast in local regions. Adaptive histogram equalization (AHE) is a method for the local contrast enhancement. AHE computes several histograms of intensity values, each corresponding to a distinct region of the image, and uses them to redistribute the intensity values. AHE is very computationally intensive and not acceptable for most applications. In this paper, we propose a method for real-time computation of AHE using an FPGA. In our system, a histogram is generated for each pixel in a image, and the intensity of the pixel is remapped using the histogram. The computational complexity of this approach is very high, but it can generate smooth enhanced images without using interpolation techniques. By reusing partial histograms by temporarily storing them in on-chip memory banks, and by adding/subtracting all bins in the histograms in parallel, we can achieve real-time processing of HD images using an FPGA. This high performance becomes possible because of the very high memory bandwidth of on-chip memory banks of FPGA.