[Didée]

Oops, my bad. Too many years of not using a programming language ... now that you mention it, I see that loopback effect.

But now, I don't see a (sane) way to do that with an Avisynth script, except you really want to run a chain of 360 times (mt_luts + mt_merge) for a 720*y frame. It should be easier to make a plugin that does the filtering in such a back-injecting way.

When looking at the resulting weights, my guess is that the effect isn't too bad. 50% of the samples used for filtering are already filtered. Those filtered samples contain 25% weight of the actual pixel ... no hard science, but since chroma filtering is quite forgiving anyway, probably it just works out. But nonetheless, a slight color shift towards upper-left is to be expected, roughly in the range of 1/4 chroma pel.