Читать книгу Multimedia Security, Volume 1 - William Puech - Страница 37

Shin et al. (2017) attempts to avoid the assumption that color channels are processed independently. Instead of working separately with each channel, as was done until then, they work on the difference between the green and red channels, as well as between the green and blue channels. This reflects more accurately the operations done by many demosaicing algorithms, which first interpolate the green channel before using the green channel’s information to interpolate the red and blue channels. They compute the variance of these differences in the four possible patterns on the two computed maps, and identify the correct pattern as the one featuring the highest variance, which is expected of the original pattern, whose pixels are all sampled instead of interpolated. Although the dependence of the color channels is hard-coded, the color difference is actually used in many current algorithms and represents a first step toward a full understanding of demosaicing artifacts.