Why did component video become a thing but not sync on green

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oldgamer
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Why did component video become a thing but not sync on green

Post by oldgamer »

What is the story behind component video (I mean YCbCr/PbPr) actually becoming a large scale thing but not RGB with sync on green?

If the idea was simply using only 3 wires/plugs RGsB would have worked for that and we would have straight RGB rather than component video which is subject to bad implementation sometimes.

Maybe because of patent problems?
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Guspaz
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Re: Why did component video become a thing but not sync on g

Post by Guspaz »

tl;dw: sync-on-luma is essentially the native base image format for all analog broadcast video, be they PAL or NTSC. When colour was added later, it was as a separate chroma channel on top of that to maintain compatibility with monochrome TVs. Essentially all compressed digital video (even today) is luma/chroma too since it works well for the perceptual trickery of our eyes being less sensitive to colour than brightness (hence why chroma subsampling exists). Even into the computer era, they were still often natively luma/chroma at the start, with computers like the Apple II adding colour support via tricks of NTSC timing to save on resource utilization.
oldgamer
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Re: Why did component video become a thing but not sync on g

Post by oldgamer »

Yeah, I had seen that video already, but checked it again. It does explain some things about component video, but doesn't really say why it became the standard as RGsB could have done it also.

Displaced gamers' videos are really good by the way.
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Guspaz
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Re: Why did component video become a thing but not sync on g

Post by Guspaz »

It became the standard because it was the logical evolution of everything else, which is luma-based. RGsB has no relation to broadcasts (analog or digital) or home media (analog or digital) which are all luma based.
oldgamer
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Re: Why did component video become a thing but not sync on g

Post by oldgamer »

Guspaz wrote:It became the standard because it was the logical evolution of everything else, which is luma-based. RGsB has no relation to broadcasts (analog or digital) or home media (analog or digital) which are all luma based.
This makes sense really, if everything else in video broadcast is luma based then it makes sense to continue doing it with luma.

But then what was RGB sync on green for then?
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matt
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Re: Why did component video become a thing but not sync on g

Post by matt »

IIRC the main reason why YPbPr became a standard in NTSC regions was because it can carry macrovision copy protection, unlike RGB. At the time, there wasn't much use for 15khz RGB, since it was no longer used by computers. The few US televisions that did include an RGB input were made in the mid to late '80s.
oldgamer
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Re: Why did component video become a thing but not sync on g

Post by oldgamer »

matt wrote:IIRC the main reason why YPbPr became a standard in NTSC regions was because it can carry macrovision copy protection, unlike RGB. At the time, there wasn't much use for 15khz RGB, since it was no longer used by computers. The few US televisions that did include an RGB input were made in the mid to late '80s.
Now this is very interesting and makes for a stronger reason as to why RGB didn't develop.

From some website:

"At issue is whether Sony Computer Entertainment has violated a DVD industry agreement that prohibits DVD players from having an analog RGB interface."

Sounds like the DVD industry did not want RGB outputs to be available, and it makes sense that it was because it would mess with copy protection.

Though by reading a bit about how macrovision protection works, it does seem like it would also work on RGB signals.


I presume european VCRs used rgb, so could they just copy stuff without being disturbed by the copy protection?
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Osirus
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Re: Why did component video become a thing but not sync on g

Post by Osirus »

Thank God the industry forbade RGB interfaces and put an end to DVD piracy once and for all.
oldgamer
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Re: Why did component video become a thing but not sync on g

Post by oldgamer »

Osirus wrote:Thank God the industry forbade RGB interfaces and put an end to DVD piracy once and for all.
I hope you're being sarcastic here, it's super awful that we didn't get RGB because of copy protection.
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Guspaz
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Re: Why did component video become a thing but not sync on g

Post by Guspaz »

It's not really awful, it doesn't really have any real advantage over YPbPr.
oldgamer
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Re: Why did component video become a thing but not sync on g

Post by oldgamer »

Guspaz wrote:It's not really awful, it doesn't really have any real advantage over YPbPr.
It kind of does though, as this requires an active transcoder to turn rgb into component, while if it was straight rgb this step wouldn't be necessary.

Also, people have figured that, in practice, rgb tends to be a tiny bit better, probably because YPbPr implementations are not always as lossless as they should. Not the end of the world, but certainly not good for the user either.
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djc5166
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Re: Why did component video become a thing but not sync on g

Post by djc5166 »

Why is the Y luma/sync connector generally green on a set of component cables? Does it actually have anything to do with green?
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Osirus
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Re: Why did component video become a thing but not sync on g

Post by Osirus »

oldgamer wrote:
Osirus wrote:Thank God the industry forbade RGB interfaces and put an end to DVD piracy once and for all.
I hope you're being sarcastic here, it's super awful that we didn't get RGB because of copy protection.
Obvious sarcasm I think. DVD piracy was pervasive and unhindered by industry restrictions like this.
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Harrumph
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Re: Why did component video become a thing but not sync on g

Post by Harrumph »

oldgamer wrote:
Guspaz wrote:It's not really awful, it doesn't really have any real advantage over YPbPr.
It kind of does though, as this requires an active transcoder to turn rgb into component, while if it was straight rgb this step wouldn't be necessary.
That’s not correct. DVD-video was the reason component input started appearing in the first place. DVD-video is native YCbCr. Like Guspaz said, continuing the luma based origins of broadcast & home video.
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matt
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Re: Why did component video become a thing but not sync on g

Post by matt »

djc5166 wrote:Why is the Y luma/sync connector generally green on a set of component cables? Does it actually have anything to do with green?
The other 2 colored plugs represent the blue and red color difference signals, so while it doesn't directly provide the green component of the picture, luma is where green is ultimately extrapolated from.
oldgamer
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Re: Why did component video become a thing but not sync on g

Post by oldgamer »

Harrumph wrote:
That’s not correct.
What do you mean that is not correct?
Harrumph wrote: DVD-video was the reason component input started appearing in the first place. DVD-video is native YCbCr. Like Guspaz said, continuing the luma based origins of broadcast & home video.
Yes, but why is YCbCr the native format for DVD-video instead of RGB? It could very well have been plain RGB.

While continuing to do it with luma does make sense, the fact that the DVD industry went to the trouble of forbidding RGB interfaces in DVD players seems to me the real, more important reason why they didn't do it.
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matt
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Re: Why did component video become a thing but not sync on g

Post by matt »

YCbCR allows for color subsampling, which is helpful for compressed video formats. RGB wouldn't be well suited.
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Guspaz
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Re: Why did component video become a thing but not sync on g

Post by Guspaz »

Yes, and it wasn't DVD specifically. The vast majority of video formats use YCbCr with subsampled chroma. DVD used MPEG-2 (1996), which YCbCr with subsampling. Before that we had MPEG-1 (1991, used on VCD and still supported on DVD, also used for some broadcast stuff). Before MPEG-1, we had H.261 (1988), designed to transmit video over ISDN, and it too was YCbCr with 4:2:0 subsampling. H.261 is notable for being essentially the ancestor of all modern video compression, as almost everything that followed it was based on it, including the latest and greatest. Before that, we had 1981's H.120, which... was used for nothing, because it was deemed too low quality for practical use, and ultimately served only as research towards H.261 as the first practical compression format. However, H.120 also used YCbCr, mainly because separated luma/chroma was the expected input format due to that being the broadcast video format that would logically be fed in, and because it allowed easy compatibility with monochrome displays by simply ignoring everything but luma. A quick look at the spec doesn't make it obvious to me if the chroma was subsampled, though.
Joelepain
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Re: Why did component video become a thing but not sync on g

Post by Joelepain »

matt wrote:YCbCR allows for color subsampling, which is helpful for compressed video formats. RGB wouldn't be well suited.
Why ?
You could compress RGB with Green in full resolution and Red and Blue subsampled and you end up with the same thing as YCbCr with chroma subsampling.
Sure you wouldn't call it "chroma" subsampling but the concept and the result is the same.

Maybe some processing algorithm are easier when you deal with YCbCr ? (like brightness/hue/saturation ajustements ?). I don't know real question here for the people who deals with that...
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Guspaz
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Re: Why did component video become a thing but not sync on g

Post by Guspaz »

That wouldn't work. You would create all sorts of bad colour fringing due to different colours being at different resolutions. Whereas with chroma subsampling, the bleed matches the colours of the surrounding objects and blends in. It also would not be quite as good at exploiting how our eyes work either. YPbPr matrices take into account that our eyes are more sensitive to green than red, and more sensitive to red than blue. RB subsampling would assign equal weight to red and blue, which is essentially making it more inefficient.
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