No-Reference Perceptual Image Sharpness Index Using Normalized DCT-based Representation

This paper presents a no-reference (NR) image sharpness algorithm based on natural scene statistics (NSS) in discrete cosine transform (DCT) domain. It relies on the assumption that natural images possess certain statistics that will change with blur distortion. We propose a new image representation, normalized discrete cosine transform (NDCT) coefficients. Both the theoretical analysis and experimental tests have proven that the statistics of NDCT coefficients are highly correlated with the human judgments of image quality. To represent the statistics of natural images, a model is built with a small set of natural images. We define the perceptual sharpness index on normalized discrete cosine transform coefficients (NDCT-PSI) as the difference between the NSS model and the tested image. The NDCT-PSI outperforms recent relevant state-of-the-art algorithms as evaluated on a subject-rated image database. The new framework we proposed here is a simple way to facilitate some practical applications.