Why did YPbPr replace S-Video for analog video?

[CursedLemon]

Just had a thought in my brain.

S-Video is a luma-chroma setup, while YPbPr is luma-chroma-chroma. Now given that the human eye has a much greater acuity for luma than for chroma, why did S-Video get briefly displaced by YPbPr before the advent of digital video? It's all copper after all, I don't think one wire is more "HD" than the other, unless the separate shielding for each wire was just that much more important.

I don't know the exact timeline for when these technologies arose so it may be a chronological thing I'm not aware of.

[Bwaak]

Because three separate components allow for cleaner separation of tristimulus values, duh. Also, (Y, R-Y, B-Y) match analog MII and Betacam, as well as digital Rec. 601.

It is not all copper. There is modulation and demodulation involved, and clean separation is not always possible.

[CursedLemon]

Because three separate components allow for cleaner separation of tristimulus values, duh.

****, it was right there in front of me!

Also, (Y, R-Y, B-Y) match analog MII and Betacam, as well as digital Rec. 601.

It is not all copper. There is modulation and demodulation involved, and clean separation is not always possible.

I figured there was probably a corresponding technology that it was based off of, but given that luma-chroma-chroma (as opposed to RGB) only arose because of broadcast bandwidth limitations, it's still inherently confusing for me that through the 17 different layers of format conversion between camera to TV that we ended up with two chroma channels at the end of the chain. But I also have no idea what I'm talking about lol

[Skiller]

Furthermore, S-Video uses one of the three common analog color modulation schemes (PAL, NTSC or SECAM), thus introducing their individual drawbacks. YPbPr does not use color modulation.

[jagabo]

With S-video the two chroma channels are modulated onto a 3.58 MHz carrier wave. The amplitude of the wave indicates the intensity of the color (saturation) and the phase of the wave indicates the hue. (With composite video the luma and chroma carrier are merged together onto a single wire and have to be separated by the receiver. With s-video, the luma and chroma carrier are sent via separate wires so they don't have to be separated. But the chroma carrier still needs to be demodulated to produce the two chroma channels). This limits the color resolution to about 1/4 the luma resolution. With YPbPr the two chroma channels are passed directly, not mudulated on a carrier, so color resolution is increased. And the signals are much cleaner.

[CursedLemon]

Ahhhh see I didn't realize that S-Video was multiplexing two different chroma channels already, that makes more sense.

[jagabo]

This article describes the situation pretty well:

https://www.nutsvolts.com/magazine/article/video_basics

[Alwyn]

Which poses the question: for us passthrough types, would it be better to use the Component Out from our DVD recorder TBCs for capture? I've done some rudimentary test comparing S-Video and Component for capture and can't see a lot of difference.

[jagabo]

Which poses the question: for us passthrough types, would it be better to use the Component Out from our DVD recorder TBCs for capture? I've done some rudimentary test comparing S-Video and Component for capture and can't see a lot of difference.

VHS has only about 40 lines of chroma resolution across the entire width of the frame. So s-video is sufficient, even with it's reduced chroma resolution. Even composite is sufficient resolution-wise, but joining and separating the chroma carrier results in dot crawl (incomplete separation of the chroma carrier from the luma) and rainbow artifacts (incomplete separation of the luma from the chroma).

[dellsam34]

why did S-Video get briefly displaced by YPbPr before the advent of digital video?

It didn't, From the beginning of analog video it was all composite (CVBS) for reel to reel and uMatic and later component (YPbPr) for pro formats, Composite continued to dominate the consumer market (VHS, Beta, Video8 ...etc) and component the pro market till the death of analog video, S-Video (Separate Video) came later on for a specific purpose and gone without much success to dominate the market, It was used for consumer S-VHS and Hi8 formats to achieve better luma bandwidth, It made no change to chroma other than the benefit of being separated which reduces interference artifacts between it and the luma even for non S-VHS and Hi8 tapes. and this is the reason why we use it today for capturing some analog tape formats as long as there is a tape deck that has S-Video socket or Y-C (BNC style).

[Sharc]

Which poses the question: for us passthrough types, would it be better to use the Component Out from our DVD recorder TBCs for capture? I've done some rudimentary test comparing S-Video and Component for capture and can't see a lot of difference.

This depends on the quality of the Luma/Chroma separating filter (simple low-pass, band-pass, or advanced (2D/3D)comb filter. It also depends on the source (effective bandwidth of the luma and chroma, and their spectral overlap).

Example: The Hauppauge USB-live 2 has a poor luma/chroma separating filter and one normally gets dotcrawl and rainbows when feeding it from composite.
The GV-USB2 does a better luma/chroma separation at the expense of a slight sharpness/details loss.

If the source is composite and one uses a (Panasonic) DVD recorder in passthrough it is recommended to use its Composite IN and S-video OUT and switch the CombFilter ON which wideley eliminates dotcrawl and rainbows do to its superior 3D comb filtering.

Whenever possible it is best to use S-video throughout.

Edit:
Sorry, forget. Above still holds, but your question was about COMPONENT rather than Composite. My bad, never mind.

[Alwyn]

If the source is composite and one uses a (Panasonic) DVD recorder in passthrough it is recommended to use its Composite IN and S-video OUT and switch the CombFilter ON which wideley eliminates dotcrawl and rainbows do to its superior 3D comb filtering.

Good to know, thanks!

[Sharc]

If the source is composite and one uses a (Panasonic) DVD recorder in passthrough it is recommended to use its Composite IN and S-video OUT and switch the CombFilter ON which wideley eliminates dotcrawl and rainbows do to its superior 3D comb filtering.

Good to know, thanks!

The question which may arise is why the "Comb Filter" should not always be switched ON.
I am not sure about the answer but I imagine it has to do with the source and signal processing steps, so just some thoughts:

NTSC (PAL) standard specifies the color subcarrier at 3.58 (4.43) MHz respectively. Luma and chroma spectra are partially overlapping in a so called "frequency-interleaving" scheme.
Frequency interleaving conditions the color subcarrier being coherently locked in a specific way to the scanline frequency. In this case, the chroma can be perfectly separated from the luma by means of a "Comb-filter", preventing the typical composite artifacts like dotcrawl and rainbows which would arise due to mutual luma/chroma interference.

On consumer tapes (VHS, S-VHS, Video8, Hi8) the luma and chroma are however arranged in a "color-under" scheme. The color components are modulated onto a subcarrier at around 630 kHz i.e. below the frequency modulated luma spectrum.

When the source for recording to tape is an NTSC (PAL) signal the chroma is separated from the luma by filtering and downconverted (heterodyned) on a 629kHz carrier ("color-under" scheme). Upon playback the chroma will be mixed (heterodyned) back to the standard NTSC (PAL) color subcarrier frequency and presented to the TV as a composite signal. By this process the original coherence of the chroma subcarrier with the scanline frequency may be lost, and the comb filtering principle is jeopardized. Simpler lowpass/bandpass ("notch") filtering at the expense of luma and chroma bandwidth (loss of details and sharpness) may give better results overall in this case. A reason to switch the Comb Filter OFF.

When the source is not from NTSC (PAL) but rather a tape natively out of a VHS videocam, the color subcarrier downconversion (heterodyning) is not applicable, and it is the VHS players responsibility to warrant the coherence between the color subcarrier and the scanline frequency upon generating the NTSC (PAL) CVBS signal, hence enabling the benefits of the Comb filtering for an interference-free luma/chroma separation.

As has been said, better to use S-Video throughout the chain if the equipment supports it as it does not use frequency-interleaving.

(Going off topic I am afraid .... )