FPGA implementation of an algorithm that enables color constancy

We designed a digital circuit that converts raw image sensor data into illumination-independent color information, and implemented it on a field-programmable gate array (FPGA). The coding algorithm used here is based on the center / surround retinex model, which is inspired by color perception of humans and by the visual signal processing in the visual nervous system. The designed digital circuit contains the following functions: integration of multiple exposure images, logarithmic compression, and difference-of-Gaussian spatial filtering. We built an image sensor system by interfacing a CMOS image sensor to the FPGA. We examined the performance of the system by presenting Mondrian to the image sensor under varying color of illumination. As a result, the system successfully reduced the influence of the color of the illumination.