The application of discrete cosine transform (DCT) combined with the nonlinear regression routine on optical auto-focusing

This paper presents a fast and accurate real-time optical auto-focusing system, which utilizes a frequency component of the discrete cosine transform (DCT) as the focus measure. Besides, a nonlinear regression routine is combined in the algorithm to quickly move a rotational stepper motor to the best focus. The concise and effective algorithm can be applied to digital cameras, microscopes and optical inspection instruments.