Quantcast How to colour grade VHS captures in Avisynth? - digitalFAQ Forum
  #1  
10-16-2020, 12:24 AM
WestRGB WestRGB is offline
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I check histograms before capture following Sanlyn's Capturing with VirtualDub [Settings Guide]

I have an intermediate understanding of color theory. I have experience in Photoshop and DaVinci Resolve. (All RGB colour spaces, mind you). But I know how to make white

I am processing my captures in AviSynth using AvsPmod, working in YUV colour space.

I have one particular tape that I'm trying to colour grade. Its an hour-long wedding video. It was poorly filmed to begin with, and I suspect a couple generations away from the original. Colours are washed out and inconsistent from minute to minute. Very dark indoor scenes and very bright outdoor scenes.

I have been trying to colour grade this tape as a whole rather than splitting it up -- mainly because there are several instances within the same shot where the histograms vary wildly. Because of these inconsistencies, I've selected conservative values in an attempt to keep legal levels across the tape.

I've adjusted the levels (y value) to appropriate values -- or at least I think I have. Correct me if I'm wrong.

I have offset the red projection (v value) by 10 to make (most of) the whites white.

The trouble I'm having now is that my highlights are too green, and my shadows are too red. I know how I would fix this in Photoshop, but not in AviSynth in YUV colourspace. Is there a way to adjust the highlights, midtones, and shadows independently? Or perhaps an alternative fix?

Script and Raw samples attached below.

Code:
FFmpegSource2("RAW1.avi",atrack=1)
ColorYUV(off_y=0, off_u=0, off_v=10, cont_u=0 ,cont_v=0)
Levels(-5, 0.9, 265, -5, 275, coring=false, dither=true)
Tweak(sat=1.0, coring=false, dither=true)
BilinearResize(720,540)
Crop(16,0,-8,-2)
Histogram("Levels")
AddBorders(12,0,12,2)


Attached Files
File Type: avi RAW1.avi (61.25 MB, 5 downloads)
File Type: avi RAW2.avi (96.75 MB, 0 downloads)
File Type: avi RAW3.avi (72.43 MB, 0 downloads)
File Type: avi RAW4.avi (98.07 MB, 0 downloads)
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  #2  
10-16-2020, 12:27 AM
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Quote:
Originally Posted by WestRGB View Post
I know how I would fix this in Photoshop, but not in AviSynth
This is why I advanced color grade in Premiere.
VirtualDub for lesser, and Avisynth only for the most basic of correction.

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- Find television shows, cartoons, DVDs and Blu-ray releases at the TVPast forums.
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  #3  
10-17-2020, 09:10 PM
WestRGB WestRGB is offline
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In the interest of simplicity, I had hoped to find a solution in AviSynth. And I did find a kind of workaround.

There's an external plugin called ColorBalance, and with it you can adjust highlights, midtones, and shadows. It only works in RGB24 and RGB32 colourspace, so using it involves converting to and back again. The results look okay to my eyes, but I'm not sure if that process degrades colour information or introduces other unwanted anomalies.
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Tags
avisynth, color correct, color grade, restore, vhs

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