Why is removing heavy dot crawl and rainbowing so difficult to achive?

[themon-master]

Hello!
As you've read from the title, I've been trying to remove heavy dot crawl and rainbowing, but I haven't gotten much luck with.

[Attachment 94272 - Click to enlarge]
As you can see, the dot crawl and rainbowing is very aggressive so I can see why it's difficult to remove.
The best results I've gotten is

clip = core.dotkill.DotKillT(clip, offset=3, dupthresh=45, tratio=1)

which doesn't remove too much, but it's a start.
I don't really have much too say, I just need help with the source.

[pandy]

Because they are inherent part of color encoding and eventual color decoding - part of spectrum for luminance signal is shared with chrominance - proper separation may be not possible.
You can try filtering in frequency domain - use some plugin or software allowing to perform signal processing in frequency domain - in avisynth you can use for example http://avisynth.nl/index.php/FFTQuiver - alternatively you can try to separate luminance and chrominance and process independently.

[Selur]

Problem is that the image was reencoded and resized multiple times and thus normal decrawler detection methods do not catch the crawlers.

applying other denoisers / grain removers on the separated fields before applying IVTC or similar might help.
i.e. TemporalDegrain2 with temporal radius 3

helps quite a bit
using TemporalDegrain and TemporalDegrain2 in succession seems to work even better.