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Old 30th October 2012, 18:55   #1  |  Link
mathmax
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adjust the levels of chroma channels

Hello

I would like to fix the problem on the bright area in the image below.

As you can see, the RGB histograms shows irregular peaks around 255: the R peak is huge, the B peak is medium and the G peak is low.

Is there a way to adjust the levels of each channel individually? Usually the levels applies on luma, but I would like to adjust each chroma channel and to cut the values above 250, this in order to wash this area to white.

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Old 30th October 2012, 19:10   #2  |  Link
Mounir
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it's best to deal with chroma in rgb in my experience although a bit of preprocess with coloryuv don't hurt , for virtualdub there are 3 filters i like: colormill , rgb equalizer and gradation curves
have a look here: http://www.engon.de/audio/vhs4_en.htm
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Old 30th October 2012, 22:02   #3  |  Link
IanB
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Use something like Levels(230, 1.0, 235, 0, 255, coring=False) to create a 0 to 255 mask of the effected areas.

Then overlay a GreyScale(), zero saturation, version of the clip into the masked areas, something like :-

Overlay( GreyScale(), Mask=Levels(230,1.0,235, 0,255, coring=False) )

Adjust the 230 and 235 values to best suit finding the aberrant pixels.
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Old 30th October 2012, 22:06   #4  |  Link
mathmax
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Thank you

I tried to play with RGB equalizer but I don't really succeed to fix this problem properly..

Would someone be so kind to have a try? Here is a short sample:
http://www.mediafire.com/?47bz11g1hf28y30

Any advices is also very welcome

EDIT: @IanB
I was thinking about something like this.. and I'll try it right now. Thank you

Last edited by mathmax; 30th October 2012 at 22:11.
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Old 30th October 2012, 22:38   #5  |  Link
mathmax
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I don't like the result so much.. :s

-first, I needed to apply Greyscale() on the mask
-second, the mask also concerns the bright part around the pink area.. and it makes it look grey, which is not the desired effect. :s

The weird thing is that this pink area should be the brightest part.. but because of oversaturation, it becomes finally less bright than the rest. Is it due to a wrong YUV<->RGB convertion?


original


mask


fixed


Last edited by mathmax; 30th October 2012 at 22:41.
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Old 30th October 2012, 22:40   #6  |  Link
TheSkiller
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What about

Code:
R=Levels(0,1,255, 0,210, false) #not tested
G=last
B=last
MergeRGB(R,G,B)
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Old 30th October 2012, 22:50   #7  |  Link
mathmax
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Quote:
Originally Posted by TheSkiller View Post
What about

Code:
R=Levels(0,1,255, 0,210, false) #not tested
G=last
B=last
MergeRGB(R,G,B)
I don't understand it..
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Old 30th October 2012, 22:55   #8  |  Link
Guest
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@mathmax

Please clarify in a PM to me regarding the origin of this video to get the thread re-opened.
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