Optimizing color fidelity in wide gamut display devices when processing images compressed by block based Discrete Cosine Transforms (DCT)

摘要

High-end monitors based on LCD technology increasingly address wide color gamut implementations featuring precise color calibration within a variety of different color spaces such as extended sRGB or AdobeRGB. However, images are often reconstructed from digitally compressed images files such as JPEG or MPEG where color quality could be questionable. In particular, when such image files are scaled up or zoomed in, different types of image artifacts become visually noticeable. Among these artifacts we find pixel repetition, blockiness, ringing, and color blotching. While pixel repetition and ringing appear due to insufficient adaptation to image context using a static or context adaptive filter kernel in temporal domain, blockiness and ringing occur due to image compression in frequency domain, when image compression factors are significant. In addition, chrominance channels often undergo an even higher compression ratio that amplifies visibility of artifacts such as color blotches. Consequently, we are interested in improving the quality of images to be displayed depending on image zoom factors. We propose to discriminate most relevant visual artifacts using power spectrum analysis in DCT domain as well as kernel based rescaling combined with statistical analysis taking into account characteristic non-stationary behavior of image content and identifiable visual artifacts. A comparative analysis based on some competitive solutions highlights the effectiveness of our approach and identifies its current limitations with regard to wide color gamut representation, primarily due to mathematical uncertainty of the studied artifacts.