How to improve this color?

[sanlyn]

Sanlyn, do you have any suggestion on this post? I regard this one as more difficult to deal with... Thank you very much for detailed replying.

https://forum.videohelp.com/threads/355281-How-to-deal-with-color-spilling

If you refer to the top photos in that post with Jason Robards, I think jagabo already answered that one. I'd suggest the same code he did (and I quote):

MergeChroma(awarpsharp2(depth=24)) # sharpen chroma 
ChromaShift(c=-2) # shift chroma left by 2 pixels

That cleans most of it, but you might want to work on the edge halo effects with DeHalo_Alpha(), which should probably work at its defaults. Another handy plugin is FixVHSOvershap (works only in YUY2). You might try learning to use pixel samplers to read pixel values, along with histograms, to help your eye spot obvious problems with those Robards shots: red is oversaturated, the images need more green, and gamma is way too high with washed-out midtones and brights. And the brights are blown away.

[xuguang_he]

Is there any software give the pixel samplers and histograms? Photoshop or sth? And I still couldn't get it clear about the idea of using this tools to help my eye spot problems. Just don't know how to proceed and what to do exactly when dealing with such sources

[sanlyn]

Working on a small demo for you. Back in a short while.

[xuguang_he]

Having meet a great guy like you is an honor for me, I couldn't be more grateful

[jagabo]

Is there any software give the pixel samplers

CSamp lets you read RGB values off the screen.

and histograms?

AviSynth has Histogram() and VideoScope(). VirtualDub has a histogram feature in its Levels filter. Also ColorTools.

[poisondeathray]

Note Histogram() in avisynth is a Y' waveform tracing

If you want RGB histogram or RGB parade , use this function by Vit
http://forum.doom9.org/showthread.php?p=1570968#post1570968

HistogramRGBLevels()
HistogramRGBParade()

[sanlyn]

Having meet a great guy like you is an honor for me, I couldn't be more grateful

Oh, my...well, hold off. Don't forget jagabo, poisondeathray, manono, etc. They've put me through the wringer on many occasions.

Thanks, poisondeathray, for those tips on Avisynth parade 'grams.

It happens that the DVD chosen to work with has tricky color problems. I'm working on a similar movie now, with even worse trouble, and it's in VHS and digital sources alike. Often these color issues are attributed to various forms of Macrovision. You can defeat Macrovision, but its after-effects can be difficult.

Maybe the following examples will show how histograms and other graphs help. Avisynth and similar tools work mostly in YUV; they show how video info is stored in the source. Most RGB histograms and scopes show the same info in different form but target the way video is displayed (ultimately all video is displayed in some form of RGB). I use both types. RGB is easier to understand IMO. Other users differ, using one or the other. Many problems are best corrected in YUV, but with this video I think RGB is also needed for final correction. VirtualDub has a free ColorTools (http://trevlac.us/colorCorrection/colorTools.html) plugin with many features. It's similar to those in Premiere, Vegas, After Effects, and Photoshop. A Doom9 thread is here: http://forum.doom9.org/showthread.php?p=458048#post458048.

You should have a pixel sampler to read pixel values. CSamp.exe is a free Windows add-in. It's somewhat fiddly and sits on the desktop (no installer needed), but it's essential and works like pixel samplers in Vegas, Premiere, etc. It can read pixel values in displays such as VirtualDub, photo apps, and many media players. Why VirtualDub doen't have one built in is a mystery to everyone.http://www.netreach.net/~gavin/gavsfreeware/csamp.htm

Below is a ColorTools RGB histogram and unprocessed frame 589 in your sample gift.demuxed.m2v (I call it "Gift1"). I used Avisynth to load the clip into VirtualDub (ConvertToRGB32(matrix="Rec601",interlaced=false)) and cropped off the borders to prevent affecting the histogram (Crop(0,124,0,-124). The histogram shows RGB response with dark colors at the left side, midtones in the middle, and brights at the right side. There are color bars for overall luma (top) and Red, Green, Blue.



The histogram shows that luma (white) is within 16-235 spec, so that's OK. But at the right-hand side, Green is extended. Red drops off early, and Blue is nonexistent past a certain point. So brights are dominated by green. Even lighter flesh tones look orange (deficit of blue). Note also the background has a purple cast.

Below: The image of frame 589 below shows how SmoothTweak's Hue operates. Here, I've increased Hue1 (SmoothTweak(hue1=8) = more blue), probably more than needed but enough to bring bright blue farther to the right to try to "catch up" with bright Green. You can see that Blue has shifted to the right, still not up with green; but the other values have shifted to the left, some below the RGB 16 target for darks, and there's more of a blue color cast. Brights are still green. You can see that YUV hue controls affect all values: changing one affects the others. So you must now play games with other parameters to restore color and luma balance. With many videos it isn't a problem. But the Blue-Green balance here is really difficult.



Now add "TV->PC": everything shifts to PC's wider color gamut -- all the way off the chart to the left. Black detail is crushed. Making the darks brighter won't restore dark detail, it grays them out. And brights are still green.



This doesn't mean you should never use Hue or other filters. It means that sometimes you get a video that's a mess to work with, no matter what you do.

[sanlyn]

I did quick YUV and RGB work on your Gift sample #1. These are learning experiences for me, undoubtedly. I used SmoothAdjust to set levels, and ColorYUV(cont_u=-100) to flatten out blue somewhat. The rest was done with gradation curves in VirtualDub. Gradation curves are another story, but they allow you to tweak very narrow color ranges. It was used to raise bright blue and lower bright green without affecting other colors. Also a bit of bright red tweak was required. ColorMill was used to compendsate for lowering green (makes the image look dimmer) by raius9ing the middle point -- that is, raising the middle point raises gamma around RGB 128 without affecting other ranges.

frames 589 and 863, after YUV + RGB. I had to use both colorspaces -- neither alone would do what I wanted. And could still be tweaked some more. Basuically, the grays are more neutral, whites are whitish but not glaring, and blacks are closer to real black. Get those shades corrected, and the rest falls into place.




An RGB histogram for the result in this scene, based on frame 586:


Note these RGB values for black, gray, and white (not always perfect, but get as close as you can):
Brightest white - RGB 235-235-235
light gray = RGB 180-180-180
middle gray = RGB 128-128-128
dark gray = RGB 64-64-64
dead "video balck" = RGB 16-16-16

Note that all three of these "colors" have equal amounts of red, green and blue. If you can get those shades close to equalibrium, other colors like pink, orange, yellow etc. should look about right.

[jagabo]

The histogram shows that luma (white) is within 16-235 spec... the other values have shifted to the left, some below the RGB 16 target for darks

ColorMill works in VirtualDub's RGB space. The target is 0-255 for RGB, not 16-235. The markers for 16 and 235 are meaningless unless you converted to RGB with a PC.601 matrix.

[sanlyn]

Yes. The bars in ColorTools can be set for RGB 0-255. I did use Rec601.

[jagabo]

Yes. The bars in ColorTools can be set for RGB 0-255.

Only the luma graph responds to that setting. And even that is meaningless because the video is already truncated by VirtualDub's rec.601 conversion of YUV to RGB. Again, unless you used a PC.601 matrix to convert to RGB before giving the video to VirtualDub.

[sanlyn]

I always specify the matrix if I expect to do anything except "quick scan" a video in VirtualDub. Histograms and 'scopes in Color Finesse have similar conventions, but they get even more complex. CF also has auto corrections and indicators for broadcast standard color and levels, monitor calibration, etc. So many settings it can drive you crazy.

[xuguang_he]

Thank you for your detailed tutorial, I'll look into it as soon as possible

[sanlyn]

Did a little work last night, will have more info later. Will be posting this later because many readers will encounter similar situations with DVD's such as this.

Maybe a better DVD issue would be the way to go. This one has serious issues. Color isn't the only problem.