Weird rainbow artifacts in capture

[cjv]

Hi,
These weird rainbow colours are appearing in my captures (mainly when diagonal lines appear, and mainly in the center of the screen).
I don't know the real name for it..thus my searches are not leading anywhere useful.
My setup consists of NTSC digital cable->SVIDEO->Radeon 7500 AIW->iuVCR 29.97fps->huffyuv (720x480).

I have tried numerous deinterlacers, pixel-lockers, smoothers, etc..with no success. If anyone knows the proper name for this..and/or possibly a filter to correct it (Avisynth if possible), I would really be interested. (or could it be possibly a hardware problem?)

http://members.shaw.ca/cjv99/rainbow.png
http://members.shaw.ca/cjv99/rainbow2.png

Thanks,

cjv

[chaumurky]

I believe this is a cross color effect. An artifact caused by the luminance patterns creating frequencies close to the chroma sub-carrier frequency. It only occurs with composite signals and as you are using s-video, It's quite possible that your capture hardware combines the signal before processing (good one ATI...) Moreover, if the material has been combined anywhere along the line between the camera and transmission, the artifacts become part of the signal - even if they are seperated later. If you've tried a temporal smoother already then I'm out of suggestions unfortunately.

[^^-+I4004+-^^]

yes,this is cross-talk all right.....it should be an
example of cross-color in books if you ask me (it's so
visible etc.)

why does it happen?
because composite video sticks luma and chroma
together and there's no way one can separate them
completely afterwards.........
so i wonder how is this (NTSC digital cable->SVIDEO
part of the process being done?
what equipment is used,etc.?
digital signals should have separated l/c all the way
(but sure that if at any point signal is converted to
composite all is lost ! as chaumurky said....)

i know that cheap bt8x8 cards have separate a/d decoders for
lume/chroma (although i can't test hat as i don't have s source...)

have you tried CNR filters?
but i doubt they'll help as this stuff has much lower frequency
(of noise) than is needed to trigger CNR's chroma noise detection...

her are a few link you should consider visiting........

http://www.cybertheater.com/Tech_Reports/Comb_Filter_Tut/guide_comb_filters.html

http://www.cybertheater.com/Tech_Archive/YC_Comp_Format/yc_comp_format.html

also some info in nearby thred:
http://forum.doom9.org/showthread.php?s=&threadid=37321

cheers

Ivo

[Didée]

Read here:

http://forum.doom9.org/showthread.php?s=&threadid=37456

cjv, you are really disappointing us - if you're looking for tips about rainbow artefacts, of course you have to search for "Guava comb".
That's really *obvious*, isn't it ...

[/HeavyKidding]

;)

[waldok]

Goes without saying, of course :D
(I was about to mention it myself... :rolleyes:

Guys, you made me a more clever man today (which wasn't quite difficult, I admit)

Waldok:cool:

[^^-+I4004+-^^]

Originally posted by Didée
Read here:

http://forum.doom9.org/showthread.php?s=&threadid=37456




oups missed that one.....guess i don't have that much cross-talk
heh

however if there were skyscrapers in my videos i know what to do now!
(LOL!)

[cjv]

Thanks for all the advice,

The guava combo, ha, who would have thought :) Actually, I have tried that filter, and all of the other "fruity" filters without much improvement. The rainbowing and other artifacts are really really really bad.

The sad thing is that it appears the problem is inside the cable box (or with the cable company itself) and outside of my control..as I can see that damn rainbowing on every digital channel (on my TV) now!!! Ha, look what I've done to myself!

I zoomed in on some captures from other channels as well and the quality is just terrible..heavy pixelation, ringing, "plastic" faces, even horizontal lines running through the picture (not interlacing but MUCH worse). All I can say is that digital cable in Western Canada really sucks. I think I am going to swith to satellite, it would probably be cheaper too!

One question...I wonder if raw mpeg2 stream rips from digital satellite would look drastically better (544x480), or if capturing analog channels and heavy filtering is the way to go?
Thanks,

cjv

[Didée]

Another approach I often used with good success is, to downsize chroma very soft, and then upsize it very sharp again:

XYZsource(whatever)

chroma = BicubicResize(width/4, height/4, 0.5, 0.0) # or /3
\ .BicubicResize(width, height, -0.333, 0.666)

MergeChroma(chroma)
Something similar to this often helped me a lot - but you have to find the right size and coeff.values.
In theory, this method is kind of :devil: , but give it a try. It often turns out astonishing good.

[High Speed Dubb]

Didée,

Actually, that’s a perfectly good (though overly agressive) 2D chroma comb filter. For NTSC material, you’ll want to divide the width and height by 2, instead.

PS: You could probably improve NTSC results by switching to a bilinear resize.