Image Restoration Preprocessing for Low Light Auto-Focusing in Digital Cameras

The performance of passive auto-focus (AF) systems suffers when operating under low-lighting conditions due to the flatness of the sharpness function. In this paper, an adaptive noise reduction method prior to AF sharpness filter is introduced for the purpose of elevating the suppressed peak in the sharpness function . Experimental results show that the use of adaptive noise reduction preprocessing enables focusing at lower lux levels as compared to non-adaptive noise reduction preprocessing.