A New Index for Assessing Quality of Solar X-ray Imaging System and Image Reconstruction

Abstract Indirect X-ray modulation imaging has been adopted in a number of solar missions and provided reconstructed X-ray images of solar flares that are of great scientific importance. However, the assessment of the image quality of the reconstruction is still difficult which is particularly useful for scheme design of X-ray imaging systems, improvement and testing of imaging algorithms, and scientific research. Currently, there is no specified method to quantitatively evaluate the quality of X-ray images. In this paper, we first propose percentage proximity degree (PPD) by considering the imaging characteristics of X-ray sources and in particular, side lobes and their effects on imaging quality. After screening a variety of imaging quality assessments through systematic testing of six aspects, we utilized the technique for order preference by similarity to ideal solution to the indices that meet the requirements. The final quality index established for X-ray image reconstruction (QuIX), consists of the selected indices and the new PPD, performs well on all the aspects, including assessment of PSF (point spread function) of ASO-S/HXI and simulation tests under different grid configurations, and imaging tests with RHESSI data. It was also found to be a useful tool in determination of proper imaging algorithm and field of view (FOV) for image reconstruction.