1. Field of the Invention
The present invention relates to a method and system for measuring the sharpness quality of video data and, in particular, to a method and system for estimating the sharpness quality of pictures without referring to the source video data.
2. Description of the Related Art
It is the ultimate goal of video experts to provide most perceptually appealing video images to viewers. One way to determine whether a resulting image quality is good or poor is to ask a panel of viewers to watch certain video sequences and to give their opinions. Another way to analyze video sequences is to provide an automated mechanism to evaluate the excellence or the degradation of the video quality. To this end, various metrics are used, i.e., sharpness, blocking, ringing, clipping, noise, contrast, and temporal impairments to evaluate the overall video-quality measure. Sharpness is related to the clarity of detail and edge definition of an image. The relative sharpness of an image can be measured, in the spatial domain, by the definition of edges in comparison to a reference image, for example. Perceived sharpness increases when objects are more clearly delineated from each other and from the background and have hard, sharply defined edges. However, in some cases increased edge contrast leads to reduction of fine details thus making sharpness and resolution opposite features.
Most of the work on sharpness in the last 20 years has been aimed at focus control for still-imaging modalities, such as photography, medical imaging, and Scanning Electron Microscopy (SEM). For example, a spatial domain approach, which is based on edge-profile acutance, uses a root mean-square gradient that is normal to the edges. In the frequency domain, Fast Fourier Transform (FFT) methods have been used based on the fact that a sharper or more focused image has more energy contained in the higher spatial frequencies. Although information about spatial coherency is not taken into account and that the measures of high frequencies are global rather than local, FFT-based methods have shown promising results. However, the main drawback of FFT-based methods has been that frequency contents are image-specific and thus they do not work in a no-reference mode, i.e., without subtracting the sharpness of the original image.
Accordingly, the present invention proposes an objective quality assessment using the video-sharpness metric based on higher order moments of the FFT spectrum to evaluate the objective quality of pictures without utilizing the source data.