Why do comb filters and decomb filters have such confusing names?

[Katie Boundary]

"This is a comb filter"
"So it gets rid of combing?"
"No, LOL, it gets rid of dot crawl and rainbowing"

Someone needs to be executed for war crimes for this.


Anyway, why is it so hard to make an Avisynth plugin that mimics a proper comb filter?

[Sharc]

"Combing" has different meanings depending on the context in which the term is used.

Basically a "Comb Filter" is a filter which has a periodicity in its frequency response, like equallly spaced notches which look like a comb in the frequency domain.

World of video:
- Comb filters are for example used to separate luma from chroma in composite video, where the chroma is spectrally interleaved with the luma.
- In the context of interlaced video the term "combing" is used to describe the visual appearance of an interlaced frame with its spatial displacement between the 2 interleaved fields. A "filter" for deinterlacing eliminates these "combes" and this process is sometimes referred to as "decombing" which has actually nothing to do with a comb filter in its original definition.

I don't quite understand what you expect from "an Avisynth plugin that mimics a proper comb filter". Giving plugins/filters more descriptive names? Difficult anyway when terms are used out of their context.

[johnmeyer]

Wonderful explanation, Sharc.

[Sharc]

Also to mention Hanover Bars of PAL video which also look like combs but require a dedicated filtering process for removing/mitigating those artifacts.

[Katie Boundary]

"Combing" has different meanings depending on the context in which the term is used.

Basically a "Comb Filter" is a filter which has a periodicity in its frequency response, like equallly spaced notches which look like a comb in the frequency domain.

World of video:
- Comb filters are for example used to separate luma from chroma in composite video, where the chroma is spectrally interleaved with the luma.
- In the context of interlaced video the term "combing" is used to describe the visual appearance of an interlaced frame with its spatial displacement between the 2 interleaved fields. A "filter" for deinterlacing eliminates these "combes" and this process is sometimes referred to as "decombing" which has actually nothing to do with a comb filter in its original definition.


Yes, I'm aware