The Purpose of Virtualdub's Chroma Smoother tool?

[Belmont]

What purpose does the Chroma Smoother tool in Virtualdub serve, exactly? Say, if you're exporting an uncompressed/HuffYUV .avi to encode in MPEG-2, wouldn't the MPEG-2 encoder already compress the color to the proper colorspace settings? I see subtle differences when playing around with it, but I just don't see the purpose of it. Can someone please enlighten me on this matter, or at least shed some light on this for me?

[themaster1]

Mpeg2 DVD is ycbcr (4.2.0) and huffyuv is 4.2.2 so there is a mismatch and you should use an avisynth script to fix that with accuracy imo such as:

mpegsource("blabla")
pointresize(last.width, last.height*2).converttoyv12(matrix="Rec601",interlaced=true).pointresize(last.width, last.height)

[lordsmurf]

Chroma Smoother is a restoration filter. It's chroma noise reduction (NR). It doesn't really have anything to do with the colorspace of MPEG or Huffyuv. It's not a reference to the same sub-topic of chroma.

Use it sparingly, otherwise you'll create "mouse trails" (temporal artifacts).

Good MPEG-2 encoders already properly convert the colorspace. I pretty much only use MainConcept Reference. Sometimes I'll use the Adobe Media Encoder, which is a MainConcept-based MPEG export from Premiere CS3 and CS4. Less often I'll use the free MPEG-2 encoding in Avidemux 2.5, but even that appears to be fine. I don't know that any special Avisynth work is needed when converting lossless AVI to MPEG-2.

I think themaster's script refers to importing MPEG-2, and then processing it.

@themaster1, welcome to the site.

[themaster1]

my fault i meant to type

avisource("blabla") #huffyuv 4.2.2
assumetff (or bff)
pointresize(last.width, last.height*2).converttoyv12(matrix="Rec601",interlaced=true).pointresize(last.width, last.height)

for vhs you'd need something more:

avisource("blabla") #huffyv 4.2.2
assumetff (or bff)
crop(0,0,0,-1).pointresize(width,height,0,0,width,height).mergeluma(last)
pointresize(width,height,0,1,width,height).mergeluma(last)
pointresize(last.width, last.height*2).converttoyv12(matrix="Rec601",interlaced=true).pointresize(last.width, last.height)

I have tested this on a smpte test pattern

[lordsmurf]

@themaster1: Be sure to put Avisynth scripts in the [code][/code] bbcode boxes.

[lordsmurf]

Actually, looking back at this, I was thinking of the temporal smoother filter's function, not this one. The temporal smoother only does temporal NR, too, not chroma NR. I just thought this was the chroma version for some reason. (I was tired, probably.) I don't even have the Chroma Smoother filter installed, because it's pretty much useless in my opinion. It's never used.