Robust focus measure for unsupervised auto-focusing based on optimum discrete cosine transform coefficients

In this paper we present a robust focus measure for unsupervised auto-focusing based on optimum discrete cosine transform (DCT) coefficients. DCT has a low computational complexity due to real-valued coefficients, and a small number of coefficients have to be calculated to achieve a good spectral representation of an image. The focusing region of an input image is divided into nonoverlapping 8 × 8 sub-images, and spectra of sub-images are obtained by 8 × 8 DCT. The focusing measure is computed from the middle frequency components. By appropriately chosen DCT coefficients, the proposed focusing measure is robust to Gaussian and impulsive noises. Experimental results show that the proposed method is more effective than the traditional methods based on the comparison with well-known autofocusing uncertainty measure (AUM).