Читать книгу Multimedia Security, Volume 1 - William Puech - Страница 36

In order to break away from a specific algorithm, Choi et al. (2011) highlights that pixels are more likely to present extreme values locally in the channel in which they are sampled and, on the contrary, to take on intermediate values when they are interpolated (Choi et al. 2011). Therefore, they count the number of intermediate values in the four positions to decide which position is the correct one. The idea that pixels are more likely to take extreme values in their sampled channel is generally true with most algorithms, which makes this method produce good classification scores. However, the probability bias can be reversed when the algorithms make heavy use of the high frequencies of other channels, which can lead to confident, but incorrect detection of certain regions of the image.