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-   -   Image/chroma subsampling on VHS and S-VHS tapes? (http://www.digitalfaq.com/forum/video-capture/9868-image-chroma-subsampling.html)

dima 07-18-2019 02:19 AM

Image/chroma subsampling on VHS and S-VHS tapes?
 
[For PAL system].
What image subsampling(chroma subsampling ?) does the images recorded on VHS and S-VHS tapes have ? 4:2:2 ?
For example: ATI 600 USB captures at 4:2:2 and Canopus ADVC(for example: 110, 300) at 4:2:0 ?
ATI 600 USB is working on PAL system ? Good I know ?

latreche34 07-18-2019 10:24 AM

Lossless capture devices usually capture at 4:2:2 10bit or 8bit depends on the capability of the card, DV devices capture at 4:2:0 for PAL and 4:1:1 for NTSC.

dima 07-19-2019 03:46 AM

Thank you so much for reply.
And you know something about this: What image subsampling(chroma subsampling ?) does originally the images recorded on VHS and S-VHS tapes have ? 4:2:2 ?

sanlyn 07-19-2019 07:34 AM

Quote:

Originally Posted by dima (Post 62620)
Thank you so much for reply.
And you know something about this: What image subsampling(chroma subsampling ?) does originally the images recorded on VHS and S-VHS tapes have ? 4:2:2 ?

Baseline DV uses 4:1:1 subsampling in its 60 Hz variant (NTSC) and 4:2:0 subsampling in the 50 Hz variant (PAL).
Digital YV12 = 4:2:0

VHS/SVHS/VHS-C (NTSC) = 4:2:2 YPbPr, similar to YUY2.

I understand that PAL analog tape is native 4:1:1 but is usually captured at lossless 4:2:2 to get a chroma resolution boost for restoration use (???). PAL users will have to confirm that, as I'm in NTSC land. NTSC analog capture to DV discards 50% of NTSC chroma besides causing other visible damage. Don't assume that capturing lower-resolution analog PAL chroma to DV makes "no difference" and doesn't cause damage: PAL analog and DV are not the same color system, plus lossy DV clearly inflicts compression artifacts and noise that don't exist in analog source, and involves unrecoverable data loss that becomes more evident in subsequent encoding stages.

PAL & NTSC DVD/BluRay = YV12 (4:2:0).

latreche34 07-19-2019 12:14 PM

Quote:

Originally Posted by dima (Post 62620)
Thank you so much for reply.
And you know something about this: What image subsampling(chroma subsampling ?) does originally the images recorded on VHS and S-VHS tapes have ? 4:2:2 ?

VHS, S-VHS are analog they don't use the same analogy for chroma as digital, Based on the bandwidth allocated for chroma it's the equivalent of 30 pixels in one scan line, It is the same for VHS and S-VHS and I believe is the same for PAL and NTSC.

dima 07-19-2019 04:14 PM

Thank you for the information. Perhaps someone else will be able to provide more information on this matter and how to compare the analogue chroma signal to digital.

Koreth 07-25-2019 01:14 AM

If you want to know more about Chroma Subsampling, the Wikipedia Article is a decent place to start. It describes the common sub-sampling ratios. One thing to keep in mind is that the the ratios described therein describe how it's done digitally. The way it's done with analog video signals like from a VCR or going to an old school TV is done by limiting the bandwidth of the color signal. The analog signals don't describe pixels, per se, but rather, changes in brightness or color as the electron beam of a TV tube is tracing across the front of the screen. The more bandwidth you have available for your luma or chroma signal, the more changes you can accurately fit into the 50-60 microseconds you have to display a single horizontal line of the picture.

It may indeed be helpful to read the various articles on Wikipedia about Analog Television, Composite Video, the NTSC, and PAL standards to get a feel for how this was done back in the analog days.

Have a look at this diagram for the signal structure of a PAL analog video signal. You'll note that the portion of the signal labelled "luminance" is a lot larger than the part labelled "chromas". This means while an analog PAL video signal can accurately contain a lot more changes in brightness than it can changes in color. But, that's okay. Our eyes are not sensitive to changes in color anywhere nearly as much as they are in brightness.

The common wisdom here seems to be to capture VHS tapes at 4:2:2, and reading up, I agree. It might perhaps be a little bit more than the amount of chroma bandwidth that a VHS or S-VHS tape can actually store, but it's better than capturing at 4:2:0, losing some of the color information and having your hands tied when you're trying to do restoration work.

dima 07-26-2019 12:43 PM

Thank you all for help so far - sharing knowledge and experience in this matter.

latreche34 09-07-2020 04:26 PM

Quote:

Originally Posted by Koreth (Post 62753)
The common wisdom here seems to be to capture VHS tapes at 4:2:2, and reading up, I agree. It might perhaps be a little bit more than the amount of chroma bandwidth that a VHS or S-VHS tape can actually store, but it's better than capturing at 4:2:0, losing some of the color information and having your hands tied when you're trying to do restoration work.

4:2:2 gives you more headroom in the chroma that allows you to do some restoration without a significant loss, Which is better NTSC 4:1:1 or PAL 4:2:0 is being debated to death in online forums for years, All I know is:

NTSC 4:1:1 has a Luma resolution of 720x480 and a Chroma resolution of 180x480

PAL 4:2:0 has a Luma resolution of 720x576 and a Chroma resolution of 360x288

If you look at it logically NTSC preserves full chroma resolution vertically where it's mostly needed since each scan line on tape has its own chroma signal. PAL preserves only half the horizontal resolution when it is not mostly needed due to the very low vertical chroma resolution recorded on tape.

Which one you prefer is up to you but no one has a choice since it's standard locked. I personally keep all my encodes in 4:2:2.


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