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10-24-2018, 01:06 AM
editor editor is offline
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Hi all,

Attached are 2 samples taken from my (VHS) JVC's hold screen, prior to starting playback.

I can see a slight grain or hash on this screen, when using S-Video - whereas Composite looks a lot cleaner.

Change of cables no difference.

Can anyone verify if I'm imagining this, and if not, will this hash make it onto my capture once playback of the programme material begins? It's hard to see when there is video playing - I can only notice it on this blue screen.

Thanks for any advice


Attached Files
File Type: mp4 svideo.mp4 (778.4 KB, 35 downloads)
File Type: mp4 COMP.mp4 (946.6 KB, 21 downloads)
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  #2  
10-27-2018, 05:12 AM
Eric-Jan Eric-Jan is offline
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You should show some real examples, this looks more like a Derek Jarman movie.
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  #3  
10-27-2018, 07:14 AM
dpalomaki dpalomaki is offline
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It really doesn't show in these samples on my monitor. The blue screen tells you about noise in the VCR's electronics, not actual video on tape.

In general an s-video connection can have much more effective bandwidth (wider frequency response) than composite for the B&W portion of the video. This is because composite signal procession can act like a low pass filter on the signal. As a result with s-video higher frequency variations in the image, such as sensor "grain" and system noise as well as real image detail, can be more apparent. For purposes of restoration it is better to capture it along with the good signal. It can be selectively filter during restoration processing.

When viewed on a typical SD TV of the VHS era (e.g., picture tube) it is largely filtered out by the bandwidth/resolution limitation, but becomes more apparent on HD gear.
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10-27-2018, 08:19 AM
hodgey hodgey is offline
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VCRs very often output noise on these screens. I've found that on my JVC and Philips (JVC "clone") SVHS decks output the composite signal on the Y(luminance channel) in the menus. It easy to see on EU models when using the scart connector as the same wire is used for Y in S-video mode and Composite video in composite video mode, so if the scart out is connected to something that accepts composite in, you get colour even when the device is set to S-Video mode. This is normal, and doesn't affect playback. When using S-Video the filters that separate out the higher frequency parts of the signal to decode colour are normally not active (since the colour is on a separate wire, and as noted by dpalomaki), so it shows up as noise instead. Different A/D Converters react differently to it, usually looks a bit different to your example, so I don't know for sure if that's what's it is as there are other things that can cause such noise like RF interference.
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10-27-2018, 11:16 AM
Eric-Jan Eric-Jan is offline
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btw... MPEG compression filters also slightly, so what you might see on your uncompressed capture (noise) might be "filtered" out in the end result.
Some people also like filtering "artefact" by using the composite connection for capturing, but it unsharps detailed information, also a prime colour like red, bleeds more out, s-video does this less, but still noticeable, with component it's allmost gone, giving a sharper picture compared to the others, although then halo or ghosting in some parts of the image is still possible.
A lot will depend on your hardware setup, it can give you more or less to do in post.
https://www.youtube.com/watch?v=D6cq9lBicPU
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  #6  
10-27-2018, 07:23 PM
dpalomaki dpalomaki is offline
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Quote:
btw... MPEG compression filters also slightly,
That's a good way to put it. To save space lossy compression removes (ignores) information in the image data stream that it deems unimportant to the visual experience; i.e., the information most people and displays cannot see because it is generally masked by other information in the image. But some of that information may be important if you are processing the image for restoration or other purposes where the data will undergo more than one cycle of compression/decompression.

The problem with composite is the Y and C information signal frequencies overlap and are mixed together in the same wire. To separate them requires sophisticated filtering, which is not 100% effective (no practical/affordable filter is). S-video keeps the Y and C signals separate eliminating the signal separation issue resulting in potentially better quality.

The C is actually signal is comprised of two (r-y and b-y) signals that have to be separated. Component provides the signals with no need to separate them which can provide an additional boost in quality over s-video. But VHS and S-VHS record C information, so it can become a question of which system (e.g., the player or capture card) does a better job of decoding the C signal if your play provide component output.

I suspect that the Y/C construct of the VCR video signal was largely driven by the compromises made to ensure "compatible color" in the 1950s when most TV sets were B&W.
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  #7  
10-28-2018, 02:36 AM
Eric-Jan Eric-Jan is offline
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My guess is, if the OP notice more artifacts on s-video, (which should not) there is some mis allignment in the electronics of the vcr, but this can't be judged by the blue (generated) screen, or the osd generator, a newscast (studio lighting) capture, and a outside report, (daylight) could tell more, judging skin tone, and contour sharpness.
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  #8  
10-29-2018, 03:50 AM
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Quote:
Originally Posted by Eric-Jan View Post
You should show some real examples, this looks more like a Derek Jarman movie.
JVC blue screens are good examples for noise.

Quote:
Originally Posted by editor View Post
Attached are 2 samples taken from my (VHS) JVC's hold screen, prior to starting playback.
I can see a slight grain or hash on this screen, when using S-Video - whereas Composite looks a lot cleaner.
Change of cables no difference.
Can anyone verify if I'm imagining this, and if not, will this hash make it onto my capture once playback of the programme material begins? It's hard to see when there is video playing - I can only notice it on this blue screen.e
You're possibly seeing tiny faint electrical interference patterns. It's a power issue. Clean the incoming power with a UPS. It probably exists on the composite, but the detail is lost in the compositing of chroma+luma (Y/C). You're not imagining it, but it's really hard to see unless enlarged. As you say, in motion, not perceptible.

Another slight possibility is the deck has a damaged solder joint or connector. Not likely, but possible. I've only seen that maybe twice in the past 20 years? Usually damaged connectors show far more severe issues, not faint noise.

Yes, what you see is what you get, it will capture. Usually. Keep reading...

Quote:
Originally Posted by dpalomaki View Post
When viewed on a typical SD TV of the VHS era (e.g., picture tube) it is largely filtered out by the bandwidth/resolution limitation, but becomes more apparent on HD gear.
I think it'll be hard to see even with modern 55"+ HD screens, especially after encoding to MPEG/H264.

Quote:
Originally Posted by hodgey View Post
VCRs very often output noise on these screens. I
his is normal, and doesn't affect playback.
Different A/D Converters react differently to it
Also true. Sometimes the noise is just on the screen, in the graphic itself, thus not on the video content. It can be an interplay of workflows devices as well. It's why I test workflows, not just individual pieces, and often mention that some devices hate others.

Quote:
Originally Posted by Eric-Jan View Post
btw... MPEG compression filters also slightly, so what you might see on your uncompressed capture (noise) might be "filtered" out in the end result.
Yep.

Quote:
Some people also like filtering "artefact" by using the composite connection for capturing, but it unsharps detailed information, also a prime colour like red, bleeds more out, s-video does this less, but still noticeable, with component it's allmost gone, giving a sharper picture compared to the others, although then halo or ghosting in some parts of the image is still possible.
Component vs. s-video should make no difference. The signal is stored Y/C, and can never get better. So s-video or component should appear identical, unless the component is doing odd filtering. And if you're seeing any ghosting, or other weirdness, then the component is filtering it heavily. And that's not good.

Quote:
Originally Posted by Eric-Jan View Post
My guess is, if the OP notice more artifacts on s-video, (which should not) there is some mis allignment in the electronics of the vcr, but this can't be judged by the blue (generated) screen
Process of elimination is required. More testing to either prove or disprove the hypothesis.

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