How to fix Chroma Bleed with AviSynth?

[VideoFanatic]

Crikey, I thought the whole video looked like it had too much sat so I turned the sat down to 0.7 via Tweak instead of 1.0. But you're saying it actually looks like it doesn't have enough colour (excluding the reds that have too much), I don't understand that.

How would a video get like that where only 1 colour was oversaturated and how would I lower the sat on just that colour?

I work on videos like this all the time and find I need to lower the sat as skin tones look too red. Yet I see stuff on TV and they have more colour without having that problem and clothes colours look more vibrant. Weird.

[jagabo]

Another useful tool is to view the chroma channels with: StackHorizontal(UtoY(),VtoY()).

[racer-x]

Anyone have any ideas on how to fix the Color Shifting on my old Dragbike at the start of this of this very old VHS shot clip?

[sanlyn]

Not sure what "Color Shifting" refers to. The mp4 has several forms of luma and chroma corruption, including chroma bleed, "blip0s" and flashes where one or both chroma channels blanks out, and oversharpening halos. Most of the problems seem due to improper deinterlace and colorspace conversion, and a low bitrate that's inadequate for the action scenes. One might be able to decode the mp4 to lossless AVI and try to fix a few things, but the bad dinterlace and chroma flashing can't be repaired -- and it would require a re-encode and more data loss.

[jagabo]

Cool. Paint that changes color!

[sanlyn]

Crikey, I thought the whole video looked like it had too much sat so I turned the sat down to 0.7 via Tweak instead of 1.0. But you're saying it actually looks like it doesn't have enough colour (excluding the reds that have too much), I don't understand that.

How would a video get like that where only 1 colour was oversaturated and how would I lower the sat on just that colour?

Lowering "Sat" with Tweak reduces saturation for all colors, not just one. You can reduce oversaturation in one channel (V is the "red" channel) with cont_v in ColorYUV(). A negative value for cont_v will help reduce the appearance of oversaturated red.

[jagabo]

V is only red. You'll be shifting other colors too.

[racer-x]

Cool. Paint that changes color!

Exactly. The footage is 22 years old. Some dude shot it with a VHS Camcorder and was kind enough to give me an analog copy. Unfortunately it deteriorated pretty badly before I digitized it about 10 years ago by capturing to a mini-dv camera.

I'm not worried about deinterlacing, I still have the transferred DV-AVI. I was just wondering if there was a way to stop the colors from changing besides converting it to Black & White.

[jagabo]

I was just wondering if there was a way to stop the colors from changing besides converting it to Black & White.

I can't think of any way to fix those flickering chroma channels in AviSynth.

[VideoFanatic]

V is only red. You'll be shifting other colors too.

How do you mean, I thought it was just said that it only changes the red?

What is the equivalent of Tweak(Sat=0.7) in ColorYUV(cont_v=) ?

Sanlyn, you said "The only color that's "too much" is red, and it's noisy. Overall, the rest looks undersaturated and washed out, yet stuff like the white arm- or wrist-band is washed out and has no detail at all". What colour corrections would you suggest to lower the red and add more sat to the rest of the picture that looks washed out?

I tried using ColorYUV(cont_v=100) and doing Tweak(Sat=1.5) but the picture doesn't look better.

[poisondeathray]

RE: the bike clip

If the psychadelic trip just affects that intro sequence, there are non-avisynth approaches that should work , e.g. a motion tracked patch repair in something like mocha / after effects

[jagabo]

V is only red. You'll be shifting other colors too.

How do you mean, I thought it was just said that it only changes the red?

Sorry, I screwed up while editing. I meant to say "V is NOT only the red."

What is the equivalent of Tweak(Sat=0.7) in ColorYUV(cont_v=) ?

Tweak(Sat=0.7) ~= ColorYUV(cont_u=-77, cont_v=-77)

[sanlyn]

True, the V channel isn't pure red, it sneaks into other hues. With YUV, adjusting V usually has some effect on U and Y depending on what's being done (contrast, offset, gain, etc). COlorYUV has no "Sat" parameter. If you want to isolate hues and chroma ranges without affecting other colors or ranges you'll have to work in RGB, or use some really kinky code with plugins like SmoothAdjust, or play around with MaskTools.

Moderate settings with MCTemporalDenoise (maybe with MergeChroma) will probably denoise the flickering in the Red, which is low-frequency noise in a low-frequency color. Or you could try FluxSmoothT(). It might have been broadcast that way.

[jagabo]

COlorYUV has no "Sat" parameter.

ColorYUV(cont_u=N, cont_v=N) is equivalent to changing saturation. When N is negative saturation is reduced, when N is positive saturation is increased.

True, the V channel isn't pure red, it sneaks into other hues. With YUV, adjusting V usually has some effect on U and Y depending on what's being done (contrast, offset, gain, etc).

Adjusting V with ColorYUV() has no effect on Y or U. You can see it clearly with this script:

function VaryV(clip vid, int V)
{
   ColorYUV(vid, cont_v=V)
}

ColorBars(pixel_type="YUY2")
Trim(0,512)
Animate(0, 512, "VaryV", -256, 256)
VideoScope("both", true, "Y", "UV")

Moderate settings with MCTemporalDenoise (maybe with MergeChroma) will probably denoise the flickering in the Red

I tried that earlier, even with settings="very high", and the flickering colors were still there, although a little reduced.

[sanlyn]

I didn't try MCTD. I don't even think the flutter can be fixed anyway. It seems to have gone through too much processing as-is.

[sanlyn]

[Adjusting V with ColorYUV() has no effect on Y or U. You can see it clearly with this script:

oops, you're right. It's not contrast that interacts. It's gain and offset. Don't know what my aging mind was thinking. My bad.

Nice demo script. Thanks.

[jagabo]

Adjusting V with ColorYUV() has no effect on Y or U. You can see it clearly with this script:

oops, you're right. It's not contrast that interacts. It's gain and offset.

No, gain_v and off_v have no effect on U or Y either. All three channels in YUV are independent. You can easily modify the script I gave to verify this. Change the line in VaryV() that reads ColorYUV(vid, cont_v=V) to ColorYUV(vid, gain_v=V) or whatever. You can also modify it to change Y or U instead of V to see each channel is independent.

I suspect you're thinking about the effects they have on RGB. A change of any Y, U, or V value can change all three RGB values. And vice versa.

[sanlyn]

Well...since video is displayed in RGB, that's the effect I'm seeing.

[VideoFanatic]

I find that this seems to work fine for this and other videos which have worse chroma bleed: MergeChroma(awarpsharp2(depth=35))

Just wondering, would that be safe to use on videos that don't even have chroma bleed? Also does the above script clean the picture in some way or does it just fix chroma bleed?

[jagabo]

That is too strong for "normal" video. You'll find small color details disappearing, colors in corners get rounded, etc.

[sanlyn]

The combination of MergeChroma and awarpsharp2 was designed to fix chroma bleed. If there's no chroma bleed, why use it?

awarpsharp2 is a sharpener. It's one of many Avisynth sharpeners. The following link has been suggested in earlier posts, but this time you might try looking at the samples on this web page: http://www.animemusicvideos.org/guides/avtech31/post-qual.html#sharpening . Look at the image and click the names of the filters below the picture to see that each sharpener works in a slightly different but visible way.

[VideoFanatic]

OK I tried the following on a different video and the ropes still look odd with chroma bleed. Any suggestions?:

MergeChroma(awarpsharp2(depth=35))
Overlay(GreyScale(last), last, y=-2, mode="chroma")

[jagabo]

Did you consider that the source is interlaced?

[VideoFanatic]

I was just quoting the part of the script that effects the issue. Here's my full script:

setmtmode(5,9)
Mpeg2Source("E:Video.d2v", CPU=6)
setmtmode(2)

McTemporalDenoise(settings="medium", interlaced=true) 

AssumeTFF() 
QTGMC(Preset="Super Fast") 
MergeChroma(awarpsharp2(depth=35)) 
Overlay(GreyScale(last), last, y=-2, mode="chroma")  
SeparateFields() SelectEvery(4,0,3) Weave()

Tweak(Bright=10, Sat=1.3, Cont=0.95, Hue=0.0, Coring=False)

Crop(2,0,-0,0)
AddBorders(10,0,8,0, $000000)

[sanlyn]

The code does work as advertised. The source has been around the block a few times; low bitrates and over filtering have degraded detail, and smeared chroma. Some elements of the fast-moving ropes have lost all color due the same cause. For video with high detail and fast action, high bitrates bare always recommended. Some of the red color has completely disappeared from sections of those ropes because low bitrates and prior processing tracked them poorly. There's nothing you can do about it.

Big mistake....
[QUOTE=VideoFanatic;2256613]

Crop(2,0,-0,0)
AddBorders(10,0,8,0, $000000)

[/CODE]
This alters the display aspect ratio of the original image, from 1.333:1 to 1.3000:1. The new encode will be a more narrow image. Instead of displaying in 4:3 as 640x480 (top image), it will display as 624x480 with side borders added to make it a 4:3 picture (bottom image):


[Attachment 19065 - Click to enlarge]


[Attachment 19066 - Click to enlarge]

704x480 is a valid frame size for DVD. It's used all the time in commercial DVD.

[jagabo]

Try adding Sharpen to the chroma Overlay:

Overlay(GreyScale(last), last.Sharpen(0,1.0), y=-2, mode="chroma")

That will bring out a little more of the lost color in the thin horizontal red lines.

[VideoFanatic]

Thanks Jagabo I'll try that.

This alters the display aspect ratio of the original image, from 1.333:1 to 1.3000:1. The new encode will be a more narrow image. Instead of displaying in 4:3 as 640x480 (top image), it will display as 624x480 with side borders added to make it a 4:3 picture (bottom image). To see the effect this has on display, click on one of the images below to user the forum picture viewr, then switch back and forth between the two images.

[Attachment 19068 - Click to enlarge]


[Attachment 19066 - Click to enlarge]

704x480 is a valid frame size for DVD. It's used all the time in commercial DVD.

Sanlyn both images you provided are the same size as each other (640 x 480) so that's not correct what you said. The original video was 704 x 480. I added borders to increase the resolution to 720 x 480 so the aspect ratio (4:3) stays the same and doesn't look squashed at all. I'm sure we've all discussed this before. I'm making a Bluray so I need to add borders to get 720 x 480.

[jagabo]

The chroma just after the Overlay without sharpen (saturation increased to make the color more visible):



With the sharpen(0,1.0):



You might try a lower warpsharp value along with the sharpen.

[sanlyn]

Sanlyn both images you provided are the same size as each other (640 x 480) so that's not correct what you said. The original video was 704 x 480. I added borders to increase the resolution to 720 x 480 so the aspect ratio (4:3) stays the same and doesn't look squashed at all. I'm sure we've all discussed this before. I'm making a Bluray so I need to add borders to get 720 x 480.

VideoFanatic, you're a nice person, and I wish you luck in your endeavor. If you don't see two black borders on each side of a 624x480 image in the bottom picture, don't come back to this forum asking why you're seeing extra black pixels on your TV with this video. Meanwhile, you can maintain the correct aspect ratio by resizing to 720x480 instead of adding black pixels. On the other bhand, maybe you want it that way. If so, thank god you're not trying for 16x9. Good luck.

[VideoFanatic]

I see what you were saying now. It would have been easier to understand if you mentioned 704 x 480 & 720 x 480 instead of 640 x 480 & 624x480. I had to look it up to see what TV resolutions you were referring to. But as I said before, we've previously discussed the issue of adding borders to 704 x 480 to make 720 x 480, I didn't even ask about that in this thread!

Anyway, I burned a 720 x 480 (704 with borders) and 720 x 480 (upscaled) video to a DVD and played it on my PS3. Both looked identical. If the 704 with borders version looks narrower, I can't see it. It must be so minor that it's not noticeable.

Thanks for the tip though. Upscaling will be useful if I ever need to make a 16:9 standard definition video on a Bluray disc. Nnedi 3 is better than Lancos4 for upscaling. When making a 4:3 video if I wanted to upscale instead of adding borders, should I double the resolution with Nnedi3 then downscale with Lancos4 to 720 x 480 or should I just use Lancos4 in the first place to upscale from 704 x 480 to 720 x 480?

Regarding the problems with the clip I posted. I tried the sharpen suggestion but I can't see any difference with and without that. I actually thought the problem with the video was that it looks like there's too much red around the ropes - they look strange. What did you guys think the problem was?