Talk:Subtract

From Avisynth

I have a doubt about how this filter works. I have an "original textless videoclip" and a "hardsubtitled videoclip" which is recompressed from the original clip, so the only differences between the two clips are the almost unnoticeable recompression artifacts and the subtitles. The point is, I want to isolate the subtitles, I mean, to have an output where the actual hardsubs are the only noticeable thing on the frame. The Subtract filter was supposed to do that job, and it kind of does it but with unexpected/unwanted results. There is the grey background, slight recompression artifacts and the subs on it, that's OK... but I can see through the subtitles! Specially when there's motion, and they were supposed to be all solid color! I've used Subtract(v1,v2) and Subtract(v2,v1) (the only difference between both outputs is that one is color-inverted) and I've used the filter Overlay with modes "difference" and "subtract" with pretty much the same unwanted result. So, is there any way to have the actual subtitles from the videoclip? What do you suggest?