Simple median-based EP PP scheme for enhancement of reconstructed Bayer colour filter array images

Abstract

In this study, the median-based edge-preserving (EP) modification is revisited and has been shown to improve effectively the quality of a reconstructed Bayer colour filter array image in terms of the composite peak signal-to-noise ratio (CPSNR) performance index. Along this research direction, the authors propose an EP-modified signal-correlation-based (SCB) post-processing (PP), called EP-SCB, as an enhancement to any existing interpolation method. The Bayer image reconstruction system they consider thus consists of two operational phases. The first phase performs an initial estimation of the missing red, green and blue colours by using an existing interpolation method, whereas the second phase applies EP-SCB PP. Since a certain class of images may not fulfil the premise of having small variations in local colour difference, which is assumed by SCBtype interpolation, thereby resulting in a deterioration in CPSNR after EP-SCB PP, a threshold test on local variance ratio is also devised to conditionally switch off the second phase. Experimental results show that the EP-SCB PP with variance-ratio test gives a worst average CPSNR than the original interpolation methods tested in none of the Kodak and IMAX image groups experimented.