Need suggestions for removing colored artifacts (chroma noise?)

[Jin Kyoichiro]

Hey everyone. I'm working on a tape that has lots of these defects (mostly green) around lights, hair, straight lines, etc. and need help to properly eliminate them. For the record, I'm using Hybrid and still relatively new to this. I found this post and spent a few hours experimenting with the filters suggested by Selur. Got decent results using KNLMeansCL denoiser on the UV fields, but had to turn up the settings quite high and it desaturates the picture to the point where some colors are nearly monochrome (see images below). Didn't notice much of a change using the other filters, so I finally decided it would be wiser to just consult the forums.



I'll also attach the source clip and a text file with the script I'm using for this test. Any help would be greatly appreciated. I tried to keep this post short, so please ask if you need more info about my workflow or anything else.

[VWestlife]

That looks like the color fringing typical of either a single-tube image sensor or a 3 tube camera whose color registration wasn't perfect. So the color fringing came straight from the camera that way, and is not a defect of the recording or capture method. Even on a live closed-circuit TV feed, it would've looked the same way.

It happened even on major-network TV shows with $100,000 video cameras:
https://www.youtube.com/watch?v=o1FDyV8kYSE

[Sharc]

@Jin Kyo: Does this look any better to your eyes? (Left=original, right=tweaked; I left it interlaced)

[Jin Kyoichiro]

That looks like the color fringing typical of either a single-tube image sensor or a 3 tube camera whose color registration wasn't perfect. So the color fringing came straight from the camera that way, and is not a defect of the recording or capture method. Even on a live closed-circuit TV feed, it would've looked the same way.

It happened even on major-network TV shows with $100,000 video cameras:
https://www.youtube.com/watch?v=o1FDyV8kYSE

Very interesting. I never would have guessed that.

@Jin Kyo: Does this look any better to your eyes? (Left=original, right=tweaked; I left it interlaced)

I think it's a bit too red but definitely an overall improvement. You removed the green bits while keeping colors intact, plus improved the saturation and contrast. How did you do it? Thanks.

[Sharc]

That looks like the color fringing typical of either a single-tube image sensor or a 3 tube camera whose color registration wasn't perfect. So the color fringing came straight from the camera that way, and is not a defect of the recording or capture method. Even on a live closed-circuit TV feed, it would've looked the same way.

It happened even on major-network TV shows with $100,000 video cameras:
https://www.youtube.com/watch?v=o1FDyV8kYSE

Very interesting. I never would have guessed that.

@Jin Kyo: Does this look any better to your eyes? (Left=original, right=tweaked; I left it interlaced)

I think it's a bit too red but definitely an overall improvement. You removed the green bits while keeping colors intact, plus improved the saturation and contrast. How did you do it? Thanks.

I used Avisynth. For the levels and color correction you can try something along the line

SmoothTweak(brightness=-20,contrast=1.2,saturation=1.2,hue1=0,hue2=5,dither=75,HQ=true)
SmoothLevels(input_low=16,gamma=1.0,input_high=225,output_low=12,output_high=235,dither=75,Ecurve=0,HQ=true,limiter=0)

I think these filters are included in Hybrid as well. Otherwise use the simpler levels() and tweak() filters. Adjust the luma to be within the 16....235 range. The black level of your capture is too high.

[Jin Kyoichiro]

Yeah, somehow I didn't notice the brightness was so high during capture. Even had it turned down a few notches from default in VDub levels. I guess it's a lesson for me to pay more attention to the histogram and an opportunity to practice color correction. Thanks for your help.

[Sharc]

Black is too high; white is too low, which makes the picture look milky/grayish.
In postprocessing use levels and/or contrast adjustments to expand the luma to the 16...235 range.
For capturing you may want to play with the proc amp settings of the capture card. Don't be fooled by the black side borders.

[Jin Kyoichiro]

Totally agree. I did lower the proc amp brightness level a bit as stated before (it's an older capture but I saved a screenshot of the levels and finished capture stats), but yeah it definitely looks like I didn't mask the black borders when previewing the histogram. I'll add this step to my notes and be sure to remember it going forward. Still would love to know some filters/settings that will remove those artifacts without being too harsh on the other colors (if it's even possible).

[Sharc]

Many ways to do color tweaking. One can manipulate levels and colors in YUV using Avisynth's ColorYUV() for example, something like

ColorYUV(gain_Y=10,off_Y=-5,cont_y=60,gain_u=-1,off_U=0,cont_u=55,gain_V=6,off_V=-1,cont_v=55)

tweak2.mp4 Left: original Right:tweaked

(Filters which work with settings for "brightness","contrast","saturation" and "hue" might be more intuitive though. Or maybe try more sophisticated color grading tools of NLE's. Eventually you may also want to apply some chroma sharpening and denoising ....)

[Jin Kyoichiro]

I've been playing around some more with KNLMeansCL and found a decent middle ground that looks vastly better than my original test clip. I'm somewhat familiar with editing in Davinci Resolve so will use it for color correction. I agree it needs more sharpening and denoising. Still experimenting but struggling to find a nice balance between too soft and too sharp. It's a fun learning experience though lol.