> These sub-pixel shifts I must admit worry me a bit. [...] Again, it seems to me that you are starting to ride the wrong horse. What we have right now is, as far as I can see, good enough to handle the specific case of slight image shifts. Please invest your energy in the *other* problem, namely to identify appearing and disappearing objects in an image, and how to increase the demerits for such cases.
Remember: We *only* need higher demerits, not an algorithm that exactly points out the problematic spots – the current algorithm already shows the differences, and we also have a blinking comparison mechanism that helps find such differences quickly by visual inspection. Werner