A new auto-focus measure based on medium frequency discrete cosine transform filtering and discrete cosine transform

This paper proposes a new auto-focus measure based on medium frequency discrete cosine transform (MFDCT) filtering and the discrete cosine transform (DCT). First, the gradient image is obtained by filtering the image with the MFDCT operator, and then the gradient image is divided into 8×88×8 sub-images. The DCT coefficients of each sub-image are computed, and finally the appropriate coefficients are selected as the auto-focus measure. Experimental results demonstrate that the auto-focus measure proposed in this paper exhibits good unimodal performance, high accuracy, and very few local peaks, and is more resistant to Gaussian and impulse noise.1