Image focus measure based on Chebyshev moments

A new measure of image focus based on the discrete orthogonal Chebyshev moments is introduced. The low- and high-spatial-frequency components of an image can be represented as the low- and high-order Chebyshev moments, respectively. The focus measure is defined as the ratio of the norm of the high-order moments to that of low-order moments. It is shown that the focus measure is monotonic and unimodal with respect to image blurring. Additionally, it is invariant to contrast changes due to the differences in the intensities of illumination. The focus measure is tested for its discriminating power of images blurred to various degrees. Noise studies show that the focus measure is robust under Gaussian and salt-and-pepper noise. The performance of the proposed focus measure is compared with the existing focus measures.