Low-Light Auto-Focus Enhancement for Digital and Cell-Phone Camera Image Pipelines

Images captured by a digital or cell-phone camera in low-light environments usually suffer from a lack of sharpness due to the failure of the camera's passive auto-focus (AF) system to locate the peak in-focus position of a sharpness function that is extracted from the image. In low-light, the sharpness function becomes flat, making it quite difficult to locate the peak.In this paper, a systematic approach is introduced to address the problem of low-light AF by performing computationally simple image enhancement preprocessing steps as part of the image pipeline. These enhancement steps elevate the sharpness function peak, leading to auto-focusing in low-light conditions. A sharpness junction quality measure along with experimental guidelines are presented for determining the most prominent enhancement steps for low-light AF. The implementation results on an actual digital camera platform are also shown to demonstrate the effectiveness of our solution.