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Standard Definition: Component vs RGB SCART ?
bookerg
17-10-2007
Hi.

I was just wondering if there was much difference between component video and RGB SCART on standard definition TV signals?

I know some standard def TV sets had component inputs (such as the Toshiba series), but couldn't accept any HD signals (not even 480p).


Does anyone have any information? Does component actually offer a (significantly) higher quality signal than RGB, or was it *only* ever used due to its higher (HD-capable) bandwidth?
tellytart1
17-10-2007
Component and RGB are effectively equivalent and you can convert between them fairly easily.

On a domestic basis, you probably won't notice any difference between component and RGB.

Conversion is easy if you think of component as being Y (Luminance), and two colour difference signals (R-Y and B-Y).

From that you can use simple maths to change between RGB and YUV.
bookerg
17-10-2007
Originally Posted by tellytart1:
“Component and RGB are effectively equivalent and you can convert between them fairly easily.

On a domestic basis, you probably won't notice any difference between component and RGB.

Conversion is easy if you think of component as being Y (Luminance), and two colour difference signals (R-Y and B-Y).

From that you can use simple maths to change between RGB and YUV.”

So component is basically just RGB, but with the "master" value only transmitted along the 'Y' (green?) wire, and the other two only carrying the "delta" (difference) values?


I remember hearing something along those lines (and this apparently frees up the bandwidth, allowing >576i signals to be carried). I still don't get the maths behind how that works, but I guess if it works, it works!
tellytart1
17-10-2007
Originally Posted by bookerg:
“So component is basically just RGB, but with the "master" value only transmitted along the 'R' wire, and the other two only carrying the "delta" (difference) values?


I remember hearing something along those lines (and this apparently frees up the bandwidth, allowing >576i signals to be carried). I still don't get the maths behind how that works, but I guess if it works, it works!”

Similar, though in practice the Y (black/white) signal is carried on the Yellow cable, or Green if using RGB cables. U and V signals use the R and B cables.

Broadcast uses this because of the way digitisation from analogue to digital is done, and the Y signal is sampled a 4 times the frequency of the colour difference signals.

Both YUV and RGB are perfectly capable of carrying High Definition signals.
bookerg
17-10-2007
Originally Posted by tellytart1:
“Similar, though in practice the Y (black/white) signal is carried on the Yellow cable, or Green if using RGB cables. U and V signals use the R and B cables.

Broadcast uses this because of the way digitisation from analogue to digital is done, and the Y signal is sampled a 4 times the frequency of the colour difference signals.

Both YUV and RGB are perfectly capable of carrying High Definition signals.”

Huh?????? I take by 'RGB' you're not referring to 'RGB SCART', though?
tellytart1
17-10-2007
RGB on a SCART has no technical reason it can't handle HD signals. However, there is no equipment on the market that can handle HD over SCART RGB that I know of.
bookerg
17-10-2007
Originally Posted by tellytart1:
“RGB on a SCART has no technical reason it can't handle HD signals. However, there is no equipment on the market that can handle HD over SCART RGB that I know of.”

But why would TV manufacturers make HD-ready TVs with dedicated component cable inputs (that CAN handle HD), but with 3 or 4 SCART sockets that can't? I mean, component cables never even took off until their 480p-capable benefits were touted. Wouldn't it have just been easier (and more familiar to consumers) if a HD-capable RGB SCART socket was developed, if it was at all possible?


I thought there was a technical issue (to do with the "redundancy" of having 3 nigh-identical signals being sent concurrently) that prevented RGB SCART from being able to handle HD?


And where does composite/S-Video and our good old friend RF fit into all this?
tellytart1
17-10-2007
Nope, no technical reason why a SCART connector couldn't handle an HD signal.

Convention seems to have decided that HD component will be either RGB or YUV (usually the TV set will be switchable) carried over a set of 3 phono cables.

S Video is poorer quality than RGB, as it carries the Y separately, and the other cable carries a multiplexed version of the two colour-difference signals.

Composite is the worst of the lot, which carries the Y signal, and the colour difference signals all multiplexed onto the same cable.

Incidentaly, composite is also capable of carrying an HD signal - we've used some old black and white 1050-line (IIRC) analogue HD widescreen monitors before at work, that were used to display the budget to the studios and galleries (was the only way to get the budget to all users, as we were not permitted to make copies of the document, or to see pages before the chancellor starts to read them).
bookerg
17-10-2007
Originally Posted by tellytart1:
“Incidentaly, composite is also capable of carrying an HD signal - we've used some old black and white 1050-line (IIRC) analogue HD widescreen monitors before at work, that were used to display the budget to the studios and galleries (was the only way to get the budget to all users, as we were not permitted to make copies of the document, or to see pages before the chancellor starts to read them).”

Do you work in parliament???


Originally Posted by tellytart1:
“Composite is the worst of the lot, which carries the Y signal, and the colour difference signals all multiplexed onto the same cable.”

What's the difference between composite and RF? Is it just the case that RF = composite + mono audio? Or is there more to it?



Btw that's a good point about the 'old' HD formats.... they must have been carried using "old" cable connections, so it makes one wonder why TV manufacturers insist on using component video for 720p/1080p :S
tellytart1
17-10-2007
Originally Posted by bookerg:
“Do you work in parliament??? ”

Nope, a news broadcaster. On budget days we get a civil servant turn up with the budget speech already printed out, and will hand it to us page by page as the chancellor reads the speech. We're not allowed to see the content of the speech until the chancellor has read it. It was usually uncovered paragraph by paragraph.


Originally Posted by bookerg:
“What's the difference between composite and RF? Is it just the case that RF = composite + mono audio? Or is there more to it?”

Analogue RF is standard definition only, and encodes the composite video onto a radio frequency, and adds the sound carriers.

Originally Posted by bookerg:
“Btw that's a good point about the 'old' HD formats.... they must have been carried using "old" cable connections, so it makes one wonder why studios insist on using component video for 720p/1080p :S”

Because there's only so much bandwidth you can get out of a single composite cable. The old analogue HD format we use is black & white only!
bookerg
17-10-2007
Originally Posted by tellytart1:
“Because there's only so much bandwidth you can get out of a single composite cable. The old analogue HD format we use is black & white only!”

Ah right. Just two more issues about this:-


(1) Wouldn't using a composite cable diminish the whole purpose of having a super-sharp 1050-line image? I would've thought a composite 1050-line image would still look weak compared to an RGB 576i image..... or is it just the case that - as it's only B&W - it renders the whole composite/RGB argument obsolete? (as only one wire is basically needed)



(2) So there *is* a bandwith issue preventing certain cables carrying HD?

RGB definitely isn't one of the victims?



oh, and:-


(3) Just out of interest, roughly what year were these TVs in use at your office? Were they ever at any point discarded (i.e. in favour of standard definition), or did they last right up until the "new" HD formats arrived in recent years?
tellytart1
17-10-2007
OK.

1) No, depends on the sending and receiving equipment, and length of cable. (The longer the cable the worse it'll look)

2) There's a bandwidth issue with any cable carrying a signal - make the cable long enough and the signal will degrade. The higher the bandwidth of the signal you're sending, the shorter the cable will be before the signal degrades.

SDI (Serial Digital - the standard definition format used by just about any broadcaster for signal movement within studios) has a transmission rate of 270Mbs (yep, nearly 3 time faster than 100meg ethernet), and using SDI grade cabling, the signal will only travel for between 300 and 350 metres before the signal has degraded too much to be able to be decoded.

There is also an HD format, called HD-SDI, which can use the same cabling, but will only travel for about 100 metres before it degrades too far to be decoded again.

3) They were used last time we did a budget special, in 1996.
Gilson
17-10-2007
Originally Posted by bookerg:
“So component is basically just RGB, but with the "master" value only transmitted along the 'Y' (green?) wire, and the other two only carrying the "delta" (difference) values?


I remember hearing something along those lines (and this apparently frees up the bandwidth, allowing >576i signals to be carried). I still don't get the maths behind how that works, but I guess if it works, it works!”

The maths is quite simple unfortunately I think Tellytart forgot to add the essential equation.

Y (Luminance) =R+G+B
tellytart1
17-10-2007
Originally Posted by Gilson:
“The maths is quite simple unfortunately I think Tellytart forgot to add the other part of the information

Y (Luminance) =R+G+B”

Not quite, there are scaling factors involved to generate the Y signal from RGB:

Y=0.299*R + 0.587*G + 0.114*B
U=0.436*(B-Y)/(1-0.114)
V=0.615*(R-Y)/(1-0.299)
Gilson
17-10-2007
Originally Posted by tellytart1:
“
Incidentaly, composite is also capable of carrying an HD signal - we've used some old black and white 1050-line (IIRC) analogue HD widescreen monitors before at work, that were used to display the budget to the studios and galleries (was the only way to get the budget to all users, as we were not permitted to make copies of the document, or to see pages before the chancellor starts to read them).”

Were these possibly 1250 line monitors? ie double line rate "625 line". I saw some demos of colour CRT HD displays based on this standard in the early 90's they were phenomenal. but of course were not broadcastable due to bandwidth. I seem to remember that it was suggested that cable or sattellite could distribute this. 1050 was the Japanese/US equivalent again as far as my memory serves me.
bobcar
17-10-2007
I just thought I'd add that component can be progressive, this alone can make a big difference depending on the makeup of the different pieces of equipment.
Gilson
17-10-2007
Originally Posted by tellytart1:
“Not quite, there are scaling factors involved to generate the Y signal from RGB:

Y=0.299*R + 0.587*G + 0.114*B
U=0.436*(B-Y)/(1-0.114)
V=0.615*(R-Y)/(1-0.299)”

Agreed but you only quoted the simplistic differences to bookberg so I quoted the same in respect of Y . On inspection not sure your expression is correct? Typo perhaps?

Edit -No its the lack of rationalisation of the denominator for U and V giving
U=0.492*(B-Y)
V=0.877*(R-Y)
Which numbers I recognise.
tellytart1
17-10-2007
Yep, I was going from Wikipedia which was showing the more complex formulae, as I couldn't remember the number off the top of my head!
Nigel Goodwin
17-10-2007
Originally Posted by bookerg:
“I thought there was a technical issue (to do with the "redundancy" of having 3 nigh-identical signals being sent concurrently) that prevented RGB SCART from being able to handle HD?”

No technical reason, just that HD is American, and America uses Component and not RGB - so all the HD gear has been Component because it's originally of American origin. Once you've got HD sources with Component, and HDTV's with Component, there's really very little purpose in modifying RGB SCART to accept HD. In any case, Component is near enough obselete, having been superceded by HDMI.
Nigel Goodwin
17-10-2007
Originally Posted by bobcar:
“I just thought I'd add that component can be progressive, this alone can make a big difference depending on the makeup of the different pieces of equipment.”

Again though, there's nothing stopping RGB being progressive either, merely that the Americans didn't use RGB so it was never developed.
tellytart1
18-10-2007
Originally Posted by Nigel Goodwin:
“No technical reason, just that HD is American, and America uses Component and not RGB - so all the HD gear has been Component because it's originally of American origin. Once you've got HD sources with Component, and HDTV's with Component, there's really very little purpose in modifying RGB SCART to accept HD. In any case, Component is near enough obselete, having been superceded by HDMI.”

Added to the fact that component HD is an analogue format, and HDMI is a digital format, capable of carrying copy protection. (I know analogue can carry copy protection as well, but it's generally easier to bypass than the copy protection on HDMI)
bobcar
18-10-2007
Originally Posted by Nigel Goodwin:
“Again though, there's nothing stopping RGB being progressive either, merely that the Americans didn't use RGB so it was never developed.”

There's nothing to stop RGB being progressive but it never is so for practical purposes that's an advantage of progressive (on some players/TVs). If my aunt had balls she'd be my uncle (old quote I know).
grabbi
18-10-2007
Originally Posted by tellytart1:
“Nope, no technical reason why a SCART connector couldn't handle an HD signal.

Convention seems to have decided that HD component will be either RGB or YUV (usually the TV set will be switchable) carried over a set of 3 phono cables.

S Video is poorer quality than RGB, as it carries the Y separately, and the other cable carries a multiplexed version of the two colour-difference signals.

Composite is the worst of the lot, which carries the Y signal, and the colour difference signals all multiplexed onto the same cable.

Incidentaly, composite is also capable of carrying an HD signal - we've used some old black and white 1050-line (IIRC) analogue HD widescreen monitors before at work, that were used to display the budget to the studios and galleries (was the only way to get the budget to all users, as we were not permitted to make copies of the document, or to see pages before the chancellor starts to read them).”


I always thought it was just another con by manufacturers to make us shell out more money for a new port on the same TV.

So, theres no reason why HD cant go through a Scart eh? This is interesting...
bookerg
19-10-2007
Originally Posted by grabbi:
“So, theres no reason why HD cant go through a Scart eh? This is interesting...”

I myself am a little confused by exactly what "HD-through-SCART" means

I mean, you could technically send a component signal down a 21-pin SCART lead (merely swapping the R,G,B pins on the device's end for Y,U,V and re-configuring a TV to do the same).... but what I mean is, could a device (such as, say, a SNES) still output the *exact* same RGB-through-SCART signal it always did, but do it in HD, or at least 480p? (ignoring, for the sake of argument, the fact that a SNES probably couldn't ever handle HD)
bobcar
19-10-2007
Originally Posted by bookerg:
“I myself am a little confused by exactly what "HD-through-SCART" means

I mean, you could technically send a component signal down a 21-pin SCART lead (merely swapping the R,G,B pins on the device's end for Y,U,V and re-configuring a TV to do the same).... but what I mean is, could a device (such as, say, a SNES) still output the *exact* same RGB-through-SCART signal it always did, but do it in HD, or at least 480p? (ignoring, for the sake of argument, the fact that a SNES probably couldn't ever handle HD)”

You could just send the signals down SCART without changing anything except the timing and max frequency (allowing for progressive as well). Signals are slightly different for 625/50 and 525/60 at the moment, HD is just SD with more pixels.

The main reason for HDMI being pushed is copy protection, the fact it's digital is a big advantage but not the huge one some would like to think.
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