[Paper] Adaptive Exposure-time Control Based on Image Entropy for Multiple-exposure-time Image Sensor

We propose an adaptive exposure-time-control method for image sensors, which can control the exposure time for each pixel to reconstruct a high-dynamic-range image, while suppressing blown-out highlights and blocked-up shadows, according to the luminance and contrast of the scene. First, the proposed method determines the exposure time that maximizes the entropy of the entire image, as an image with high entropy contains more object details. In order to estimate the exposure time appropriate for the light and dark areas in the scene, the proposed method divides the image into blocks and estimates the exposure time that maximizes the entropy for each block. Because the proposed method captures and estimates several exposure times simultaneously, the time required for adjusting the exposure time is reduced. Simulation experiments show the effectiveness of the proposed method.