Quantcast Chroma delay on Laserdisc? - digitalFAQ Forum
  #1  
05-07-2018, 12:59 PM
metaleonid metaleonid is offline
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Hello,

Been a long time.

My LD player LD-S2 shifts chroma a bit. In order for 3D filter to work perfectly, this has to be corrected. I'm able to delay chroma using Allen Avionics VAR-256 device. My workflow is to split S-Video into luma and chroma channels, run the chroma channel through Allen Avionics VAR-256 device and then plug luma and chroma channels into Extron YCV 100 to get composite output. This is not a problem.

My problem is to find the optimal delay value. I don't know how to scientifically eye the correct value. Thus, I was curious if I send a few test samples including Snell&Wilcox with various values, will some be able to advise me which delay value should be optimal? Thanks in advance.
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  #2  
07-10-2018, 08:09 AM
metaleonid metaleonid is offline
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Lordsmurf, do you think you can help?
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  #3  
07-10-2018, 09:14 AM
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lordsmurf lordsmurf is offline
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Test capture, then plugin into Avisynth. Eyeball it there, figure out values. To help, you can also offset it.

That's not something I've really dealt with very often. Usually, it;s due to the device embedding the error in a tape. And it can still mostly be fixed, even after tape embedding. The magic of Avisynth.

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07-10-2018, 09:18 AM
metaleonid metaleonid is offline
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But how do you do it in AVISynth? Care to send me the script samples?
Also the end result must be Composite video fed into motion adaptive 3D comb filter. That’s why I can’t be correcting in AVISynth. Only eyeballing it. But do let me know the script.
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  #5  
07-10-2018, 02:54 PM
sanlyn sanlyn is offline
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I don't think anyone can give you a working script without a sample of the problem you're asking about. What do you mean by "chroma delay"? Do you mean chroma ghosting from blended-field processing? Chroma ghosting from preceding or following frames? Chroma bleeding or displacement?
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07-10-2018, 03:01 PM
themaster1 themaster1 is offline
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avisource
assumetff()
separatefields()
A=Last
B=A.Greyscale()
Overlay(B,A,X=0,Y=-2,Mode="Chroma") # change X or Y or both values
weave()

That's how you do in avisynth for interlaced video

If you want to fix the chroma automagically (not so magic actually, many errors but haven't tried in a long time) try the plugin AutoChromaFix
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  #7  
07-10-2018, 05:11 PM
sanlyn sanlyn is offline
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How do you know the video is interlaced? What if it's telecine? We still don't know what the poster means by "chroma delay".
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07-10-2018, 07:44 PM
metaleonid metaleonid is offline
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Sanlyn, I believe it is called bleeding.

The explanation:

This is the example of Y/C delay error: https://mediaarea.net/_/img/QCTools/image60.jpg
This is corrected: https://mediaarea.net/_/img/QCTools/image61.jpg

I am attaching 4 screenshots. Take a look at Snail&Wilcox screen shots one run with 99 nano seconds delay (AvionicsDelay99.PNG) and the other one run without (NoDelay.PNG).
Take a look at the bottom right center where it says 1.5. You can see that the image that was run with chroma delay has full chroma resolution. This is not the case when it was run with no delay. However, I am not certain 99 nano seconds is the optimal value.

themaster1, this script is for correcting delay, right? Not to eyeballing delay, right? I will need to correct delay in hardware and to eyeball it in AVISynth. The reason is, I split luma and chroma, then correct chroma, and then I need to comb them to run through motion adaptive 3D comb filter. The input to the comb filter should have chroma corrected.

2 more screenshots. TestPattern1NotCorrected.jpg and TestPattern2Corrected.jpg.


Attached Images
File Type: png AvionicsDelay99.PNG (591.5 KB, 16 downloads)
File Type: png NoDelay.PNG (570.6 KB, 14 downloads)
File Type: jpg TestPattern1NotCorrected.jpg (14.0 KB, 9 downloads)
File Type: jpg TestPattern2Corrected.jpg (37.7 KB, 9 downloads)

Last edited by metaleonid; 07-10-2018 at 08:12 PM.
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  #9  
07-20-2018, 11:37 AM
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@sanlyn: I think metaleonid knows enough that it's not a case of simple telecine. So that the assumption I'll go on for now.

@metaleonid: If it truly is a chroma delay, then an Avisynth script to correct it is what you'll do. What themater1 provided will probably work fine. If I'm deciphering it correct, the -2 value is the temporal offset. Probably -2 frames, but read the filter documentation. Or ask themaster1 for clarification.

If it is -2 frames, and you need timecode, then break out the pencil for some basic algebra. The frames are either base25 or base29.97(then rounded), and 2 frames is about 1/12th or 1/15th of seconds (base60). You may be able to find a dummy calculator online, but I prefer the math.

I'm not sure what timebase S&W is using there, assuming base60 standard seconds.

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  #10  
07-20-2018, 04:45 PM
themaster1 themaster1 is offline
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The script i gave you is to fix chroma shift manually (move chroma up ,down, right,left basically) not sure if that was what you were looking for. (you have to eyeball and change X=,Y= values according to your needs)
Autochromafix can do that automatically. Last time i checked it wasn't bad, but not 100% safe and very slow
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  #11  
07-20-2018, 05:47 PM
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Quote:
Originally Posted by themaster1 View Post
The script i gave you is to fix chroma shift manually (move chroma up ,down, right,left basically) not sure if that was what you were looking for.
Unless I'm reading it wrong, he wants temporal offset.
I guess it's time for him to re-explain his needs, as I'm no longer sure either.

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  #12  
07-20-2018, 11:23 PM
metaleonid metaleonid is offline
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Hello,

I’d like to fix it but not in the AVISynth. My workflow is:

S-Video out with breakout cable where chroma channel goes through a delay line. Then luma and chroma channels go to Extron VYC-100 which combs them together. Now I get composite signal with the correct sync between luma and chroma. The composite signal is then going to a capture card with motion adaptive 3D comb filter. The motion adaptive 3D comb filter is the reason why I want to fix the delay before analog to digital transfer because for the filter to work properly luma and chroma must be in sync. If I do it in AVISynth, the signal is already incorrectly transferred to digital which is unfixable.

What I want to do is to eyeball he delay and adjust it it.
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  #13  
07-21-2018, 03:51 AM
themaster1 themaster1 is offline
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It's not an issue to fix the chroma shifts after analog>digital convertion especially if you use a lossless codec.
You're working with a good source material (laserdisc) so the shift should be constant throughout, unlike old vhs recordings that i work with sometimes; so it's a piece of cake i'd say.
A 3D comb filter only work on chroma artefacts, it fix cross-colour interference or colour bleeding and don't take Luma into account or it's spacial position relative to chroma.
That's my 2 euro's cents
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  #14  
07-21-2018, 09:00 PM
metaleonid metaleonid is offline
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No, I wasn't able to bring full chroma resolution back. Also I am including 4 more screenshots from Video Standard LD player. There are 2 samples. The player Pioneer CLD-D703 exhibits no delay or very minimal one which is not worth correcting. The player Pioneer Elite LD-S2 exhibits delay such that to the right of red vertical bars there is a tiny black line on the right edge. Please take a look.


Attached Images
File Type: png CLD-D703 red bar on yellow.PNG (524.3 KB, 5 downloads)
File Type: png LD-S2 red bar on yellow.PNG (506.2 KB, 5 downloads)
File Type: png CLD-D703 red bars on white.PNG (443.9 KB, 5 downloads)
File Type: png LD-S2 red bars on white.PNG (415.0 KB, 5 downloads)
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  #15  
07-22-2018, 03:58 AM
themaster1 themaster1 is offline
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i don't see the black line on the right, i need glasses perhaps.
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  #16  
07-22-2018, 03:31 PM
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The "black lines" are internal sharpening (edge contrast) from the player. Common trick.

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07-22-2018, 07:51 PM
metaleonid metaleonid is offline
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Quote:
Originally Posted by lordsmurf View Post
The "black lines" are internal sharpening (edge contrast) from the player. Common trick.
Fair enough. But the black lines on LD-S2 screen shots are only to the right of red bars. On CLD-D703 screen shots it is symmetrical on both sides.
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  #18  
07-22-2018, 07:58 PM
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Black is usually paired with white. So black on right, white on left.
But some can be black and black.

You're probably running into the sharpening of the Laserdisc players. Most consumer stuff does that. LD was only consumer, so I'm not at all surprised by it. Whether it's good or bad is debatable.

Sharpening doesn't really have much to do with chroma.

LD is one of the few areas of video where I never dabbled directly, always supported others. I'd been offered players and discs many times in past years, sometimes even for free, but circumstances at the time made me decline. Even now, honestly, I'm not sure if it's something I'd want to mess with. I'd rather give an LD to somebody like you, if ever I wanted one processed.

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  #19  
07-22-2018, 08:00 PM
metaleonid metaleonid is offline
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Ok, but how would you explain that in my 1st screen shots cyan bars on snell and wilcox appeared only when I delayed chroma by 98 ns?
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  #20  
07-22-2018, 08:02 PM
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Quote:
Originally Posted by metaleonid View Post
Ok, but how would you explain that in my 1st screen shots cyan bars on snell and wilcox appeared only when I delayed chroma by 98 ns?
I'm not sure what you mean, nor what I'm looking at.

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