How does the shape descriptor measure the perceptual quality of the retargeting image?

Perceptual quality evaluation of the retargeting image plays an important role in benchmarking different retargeting methods, as well as guiding or optimizing the retargeting process. The distortions introduced during the retargeting process are mainly categorized into shape distortion and content information loss [1]. The shape distortion measurement is critical to the evaluation of retargeting image perceptual quality. In this paper, the performances of different shape descriptors, such as PHOW [2], GIST [3], MPEG-7 descriptors [4], EMD [5], for evaluating the perceptual quality of the retargeting image are examined based on the public image retargeting subjective quality database [6]. Experimental results demonstrated that most of the shape descriptors can hardly capture the characteristics representing the quality of the retargeting image, but the global shape descriptor GIST [3] presents significant performance gains. Moreover, by incorporating with the measurements from the perspective of content information loss, a better performance is further obtained.