Selection of good display mode for terahertz security image via image quality assessment

In order to provide a good display performance for THz (terahertz) security image, we designed several display modes on the custom-built THz security image database (THSID). Based on our statistical analysis of THz images, a total of 4 candidate display modes are proposed, namely averaging the highest 1%, 10%, 20%, 30% pixel values in Z-axis for a coordinate (x, y). In this paper, the subjective evaluation was first carried out, demonstrating that the second display mode, that was the averaging the highest 10% pixel values in Z-axis, got the greatest performance. Subsequently, to further support the result obtained by the subjective evaluation and the high throughout application requirement in real world, a total of 11 objective no-reference IQA (Image Quality Assessment) algorithms were implemented, including 4 opinion-aware approaches, viz. GMLF, NFERM, BLIINDS2, BRISQUE, and 7 opinion-unaware approaches viz. CPBD, FISBLIM, NIQE, QAC, SISBLIM, S3, Fish_bb. The results of objective evaluation show that the current objective IQA algorithms can hardly support the subjective evaluation. Even so, BLIINDS2 and CPBD perform relatively well for the chosen display mode above. A more suitable objective evaluation method need to be explored in the future study. This study will make some progresses on the display effect of THz image, which can promote the detection accuracy in the future applications.