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  #1  
07-18-2019, 02:19 AM
dima dima is offline
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[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 ?

Last edited by dima; 07-18-2019 at 02:31 AM.
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  #2  
07-18-2019, 10:24 AM
latreche34 latreche34 is offline
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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.
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07-19-2019, 03:46 AM
dima dima is offline
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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 ?
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  #4  
07-19-2019, 07:34 AM
sanlyn sanlyn is offline
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Quote:
Originally Posted by dima View Post
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).

Last edited by sanlyn; 07-19-2019 at 07:45 AM.
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07-19-2019, 12:14 PM
latreche34 latreche34 is offline
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Quote:
Originally Posted by dima View Post
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.
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07-19-2019, 04:14 PM
dima dima is offline
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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.
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  #7  
07-25-2019, 01:14 AM
Koreth Koreth is offline
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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.
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  #8  
07-26-2019, 12:43 PM
dima dima is offline
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Thank you all for help so far - sharing knowledge and experience in this matter.
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