Basic Question:Denoising what is prefilter and reference clip

[avinewbie]

Hi,
1)

Am trying to understand in denoising, how does prefilter of the video help to additionally denoise?

2)
What is"reference clip"?
How does it help in denoising?

Does it mean the prefiltered video?

I could not find much info about this-
Hope someone can explain?
Thanks

[StainlessS]

how does prefilter of the video help to additionally denoise?
Well if doing some kind of motion compensated denoising,
pre-filtered clip might be source clip with eg UnDot style prefilter applied, so that motion analysis might be done on the prefiltered clip,
but motion compensating done on the source clip by applying prefiltered motions vectors to the source.

I'll pass on the reference clip thingy [also might want to say in what script / script function "reference clip" refers to].

[avinewbie]

Thanks you StainlessS

So a prefiltered clip is the video that has been denoised that is used by the main denoising Programe ( like SMDegrain) in order to obtain motion vectors.
I presume this is to improve the denoising quality in the original video by using the motion vectors?
If this is correct what type of denoising is good to apply to produce the prefilter clip?--very strong denoising?( which normally would cause detail loss)

[ChaosKing]

It depends on the video, there is no denoiser that fits all types of video. You can even feed smdegrain into smdegrain as a prefilter.
Search for "prefilter" on the wiki page, it has some usefull information about prefilter http://avisynth.nl/index.php/SMDegrain

[StainlessS]

Something like UnDot (simple spacial filter) can produce better, more reliable temporal vectors for the actual denoiser. [even spatial blur() can help]

EDIT: dots and stuff, can screw up / make for less relable, vector analysis.
Given that noise is the problem to solve, and noise inhibits good vector analysis,
so gettin' rid of some noise for pre proc and vector creation, is a good thing.
After motion compensation via motion vectors, the denoise actual, can still use the
original noisy dotted motion compensated clip/frames, and denoise that.

EDIT: pre filter should best be spatial.

mobile:

[avinewbie]

Thank you for those valuable tips and insights Stainless S.

Thanks Chaosking, I have read the SMdegrain doc but don't fully understand much. It does work well for me by trial and error:)