Abstract: Degree of target being confused （DTC） and degree of target being shielded （DTS） are two valid metrics for estimating the quality of small infrared target images, but they can not describe the quality of large target images. In this article, the two metrics are redefined to realize the unified description of infrared images with various target sizes. First the calculation method of the metrics for small target images is modified, and then new calculation algorithms is proposed for the cases when the target is large. For small target images, the values of these two metrics show, respectively, the ability of the background to provide false alarm and its ability to shield the target. In large target images, their values reflect respectively the similarity degree between the background region and target region and the departure degree between the target information and the known information in an ATR system. Theoretical analysis and experiment results show that the proposed metrics are more valid than the traditional signal-to-noise ratio （SNR） and clutter metrics, while their values are in better agreement with the actual target.

Key words: image quality, performance evaluation, automatic target recognition, infrared imaging, degree of target being confused, degree of target being shielded