Super-resolution Image Reconstruction from Projections Using Non-local and Local Regularizations

This article presents a super-resolution (SR) method dedicated to tomographic imaging, where an image is reconstructed from projections obtained with low-resolution detectors. In this work, upscaling the image resolution is performed by backprojecting the projection measurements into the high-resolution image space modeled on a finer grid. Since this upscaling process often creates irregular pixels, it is important to employ regularizers that can reduce the irregular pixels while preserving fine details. Here we consider two different types of regularizers, non-local and local regularizers, each of which has been independently used for image reconstruction and is known to have its own advantages and disadvantages depending on the edge structures in the underlying image. To achieve a good compromise between the two types of regularizers, we selectively combine them using a space-variant weighting factor, which is systematically determined by our own criterion to classify edges. The experimental results show that our proposed SR method improves the reconstruction accuracy in various image quality assessments and has the potential to be useful in a wide range of imaging applications.