Component Vs RGB (Scart?) Vs Svideo Vs Composite

[Nic Rhodes]

Not sure this is the right place for this, moderators feel free to move if necessary.

Right this has come up repeatedly over the last few months so I thought I would try and quantify the differences for people to understand. It is not meant as a technical description as Richard A has done this already on this site. More a practical why.

Signals are stored digitally on DVDs in a natural component form. This is also known as colourstream (colorstream?) or YPbPr colour difference. Component is a high quality interface. It is an American system. It comes in interlaced and progressive versions. It is cheap, reliable and high quality. Cables are also cheap.

RGB is another high quality interface. It also comes in interlaced and progressive versions. It is most commonly seen on computers where we use a 5-connection system RGBHV (Red Green Blue Horizontal sync Vertical sync). It is how most computer monitors are driven (HD 15 connector to CRT monitor showing VGA, SVGA, XGA etc are all RGBHV). There are numerous other versions. A 4 wire one where the sync signals are combines. A three wire hides the sync signal on one of the colour signal. RGB signals in general come through a variety of physical connector. The best are BNCs, then we have ordinary RCA / Phono plugs all the way down to SCARTs (the worst connector in the world?), designed by a committee (quote Ian J!). I think we can blame the French for hoisting this one on us, as previously it was known as a Peritel connector. It uses RGsB on some of its 21 pins. This is an interlaced ONLY version, the Gs means a sync signal on the G. The connector also has the ability to transfer Svideo and composite as well. It really is the lowest of the low re RGB signals. Signal levels are lower than other RGB signals and are therefore not easily matched / interfaced without additional electronics. (Scart to projector / plasma (without SCARTs sockets themselves) is a no no without additional electronics).

To be strictly accurate RGB is a component signal, however in reality the day to day terminology is different. Component refers to YPbPr (USA) signals and RGB is usually UK Scart RGB.

To get a RGsB Scart signal a conversion needs to take place within the DVD player. This is easily accomplished with MINIMUM degradation. However many TVs manufacturers are international now and use internal chipsets to make the TVs. This means that much of the digital wizardry is done internally in a natural component form (NTSC based American world) (this is why Lowe TVs can accept either RGB or Component via a non-standard Scart). This means that the RGB Scart signals need to transpose back into component. Again not difficult but not really necessary.

Now we need to look a bit closer at the difference between RGB and component. Basically component signals are LESS susceptible to colour errors (instability and phase) than their RGB brothers. Feed either to a PAL TV and you really shouldn’t see much difference (other than the extra stage of conversion the RGB Scart signal needs to go through to be converted into component internally). Look for TV with native component inputs is good advice. PAL is actually a very nice system and is more robust. The American use NTSC and this isn’t as robust. They NEED component signals to keep quality. Feeds them a RGB signal and NTSC suffers from colour instability problems in comparison. Hence, NTSC Never Twice the Same Color! These are the reasons why I recommend component over Scart RGB. It is easily demonstrated. Add into the equation that PROPER component cables are cheap (well-screened 75 ohm co-ax, 50p / m?) it starts to look very rosy against you silver wired RA Scart for £250. Hells even the £50 IXOS / QED SCARTs looks expensive in comparison.

For transferring DVD signal I recommend component signals. For transfer higher resolution signals (scaler to projector) I recommend proper RGBHV. Given the preference I would do all on BNCs.

Svideo can be best thought of as a cut down 2-wire version of component. It therefore retains many of the advantages of component signals. It is a stable system that works with both NTSC and PAL. Some players like Tag and Toshiba’s have been shown to have better Svideo performance than any RGB Scart for just these reasons. It is down to the quality of engineering. Again the internal TV chipsets are more SVideo aware than RGB Scart aware. We are now in the realms of bigger differences between the connectors than the interface standard. SCARTs are really bad, with emphasis on BAD, phonos are better, Svideo mini din is a bit better again but by far the best connector is the BNC. This is why top products will output EVEN their Svideo signal on BNCs given the option. My Tag can output a Svideo signal on 2 mini dins and a pair on BNCs (for ultimate quality on Svideo).

At the bottom of the pile is the poor old composite signal. It is actually not as bad as many want to make out. Don’t forget this is what analogue TV a laserdiscs use. It can produce an excellent picture in it’s own right so don’t dismiss some just because it only as composite. Ever seen the Arcam TV box at play? It is composite.

Any conversions in either direction will cause degradations, as will any cheap switching box. However when done well you should not be able to see any degradation to the signal (most receivers nowadays will pass interlaced signals with no visible degradation). Unfortunately the reality is there are more conversions going on than we perhaps realise.

A rule of thumb

Component > RGB Scart <> Svideo > composite

This is the best order on interfaces but connectors / engineering / transposing formats can certainly reverse at least the middle two Svideo and RGB Scart.

I just wish Scarts were not so damn convenient, if we rated them on performance



Hope this helps someone.

Nic - another very interesting point you've brought up!! I cannot comment on component, but after what you've said I'm definitely going to try S-Video on my Tosh SD-900E, as I've never been blown away by the video performance of this player, and I always expected to be based on the reviews!

Thanks!

[CJROSS]

Moderators - My Vote For A Sticky Please !!

[MartinImber]

PAL / NTSC do not exist in RGB land - it is 625/50i or 525/60i

DVD players normally use sync on composite, however Nokia mediamaster uses sync on green

Assuming all is equal RGB is better than SVideo as colour resolution is higher.

Component / RGB conversion should be lossless either way

Connecting DVD or DVB to TV will require one Component to RGB conversion as RGB drives the tube.

[kevenh]

Ain't RGB a full bandwidth signal, and american component bandwidth limited?
I guess it's a good idea to try all the output choices you have available. End of the day, use what output you like.


Also, why do they convert to component inside a TV when CRTs use RGB guns?
Must do it to make it easier to adjust brightness, and other things

[MartinImber]

>>Also, why do they convert to component inside a TV when >>CRTs use RGB guns?
>>Must do it to make it easier to adjust brightness, and other >>things

Also 100Hz uses it

my 50Hz TV doesn't do RGB-Component-RGB

[Nic Rhodes]

Originally posted by MartinImber
PAL / NTSC do not exist in RGB land - it is 625/50i or 525/60i

Quite correct by as I said in the original post all is not as simple as it first appears. Why can some DVD players output RGB signals and be only PAL compatible? If it worked as you have said it would always work, it doesn't.

Originally posted by MartinImber
DVD players normally use sync on composite, however Nokia mediamaster uses sync on green

As I indicated there are many versions of RGB and the syncing arangements. I didn't want to get too technical as I feel we loose many readers..

Originally posted by MartinImber
Assuming all is equal RGB is better than SVideo as colour resolution is higher.

Agreed but this is not a level playing field.

Originally posted by MartinImber
Component / RGB conversion should be lossless either way

Agreed, said basically that in the original post.

"To get a RGsB Scart signal a conversion needs to take place within the DVD player. This is easily accomplished with MINIMUM degradation."

Originally posted by MartinImber
Connecting DVD or DVB to TV will require one Component to RGB conversion as RGB drives the tube.

Nice idea but the reality is often different. Why didn'y my old philps 50 hz show NTSC colour when run in RGB?

Ain't RGB a full bandwidth signal, and american component bandwidth limited? [/B]

RGB signals can certainly be a much higher bandwith than component hence I said

"For transferring DVD signal I recommend component signals. For transfer higher resolution signals (scaler to projector) I recommend proper RGBHV. Given the preference I would do all on BNCs."

Originally posted by MartinImber
why do they convert to component inside a TV when CRTs use RGB guns?
Must do it to make it easier to adjust brightness, and other things

Brightness, contrast, 100 hz and all those gizmos but it does appear on 50hz sets as well. Personally I think this a shameas I would much rather have 50 hz than 100hz but would prefer to hold out for progressive done correctly.

Remember the old Faroudja video processors (3000 / 5000?). They took component signals in and converted them to SVideo before doing the DcDi thing but they still component sockets on the thing.

What I am saying is be aware of how these devices work and try things out to see what works best for you. Some makes work really well with RGB, others less so. It is all down to the engineering and how things are done.

At the end of the day, if RGB Scart is so wonderful why don't we use it in plasmas and projectors routinely? Component rules the day here, ever wondered why?

[MartinImber]

Well component was originally invented in the UK by BBC AFAIK to allow easy conversion to B&W

Well my TV is definately RGB from Scart to tube with no conversion - same with the DTTV tuner - makes pal look bad!

There are no SVM artifacts on any RGB source, I have use SVid sources and I was unimpressed.

As to projectors using component - broadcast standards again, also a world standard RGB is a computer and Europe standard

My old 25" TV (one with DTVA) doesn't do NTSC via composite, but does display RGB 525/60i - also I was unable to tape (a test thats all) and the head motor was going ape.

Theoretically using top end components via similar cables RGB and Component would be identical and SVid would be noticably worse

[Gordon @ Convergent AV]

Nic, Excellent post.
Martin, good points.

I am currently investigating an interesting anomoly I've found with Component in to Loewe tellies...in either RGB or YPrPb form...s-video(also component) is not affected. I don't want to say what it is yet until Loewe have had a chance to tell me if they will do anything about it...

I'd agree with Nic that you have to forget about theory and look in to what works in practice...if indeed anything does!

Gordon

Gordon......
Loewe, Component / RGB .............i'm interested!

Adzman

[Reiner]

Nice idea but the reality is often different. Why didn'y my old philps 50 hz show NTSC colour when run in RGB?

Because it may have downconverted to S-Video. If you feed a RGB Signal into a TV and it allows adjustment of brightness and color you can be sure it's downconverted to component or S-Video. After that you need to upconvert it back to RGBHV.
IMHO 50 or 100Hz has nothing to do with it.

Vaguely on-topic here; I tried using S-Video on my SD900E, and after a considerable amount of jumping between that and RGB SCART, I prefer SCART. The picture was clearer, more detailed. I can only assume my dissatisfaction with many films is simply due to the fact that...maybe the player is pulling out too much detail? The biggest problem is with visible digital compression artifacts.

Of course, stuff like LOTR and Gladiator look absolutely stunning, but less well transferred stuff can be quite ugly (that'll teach me to be a Star Trek: TNG nut I suppose!).

[Nic Rhodes]

Originally posted by Reiner
Nice idea but the reality is often different. Why didn'y my old philps 50 hz show NTSC colour when run in RGB?

Because it may have downconverted to S-Video. If you feed a RGB Signal into a TV and it allows adjustment of brightness and color you can be sure it's downconverted to component or S-Video. After that you need to upconvert it back to RGBHV.
IMHO 50 or 100Hz has nothing to do with it.

Agreed Reiner, hence my Faroudja example of how even the high end use these common techniques. However there is a belief that they are using a 'purist' videophile approach. i.e. RGB going straight to the RGB guns. The reality (for all tvs?) is much different and the reason I wanted to 'raise' the topic.

Visual artifacts are a fault of the poor quality of tv internals and is the reason why I describe all tvs as flawed. Proper scaling / de-interlacing to a projector / plasma easily shows all the faults. I know of NO tv that does an acceptable job here.

[Nic Rhodes]

Quote from Joe Kane, godfather of video

“……..It is often accomplished by converting the incoming component signal to S-Video, then sending that signal to their standard decoder chip. Believe it or not, this is a common practice, not only among TV set manufacturers, but in several video upconverters. There is a picture quality loss going from component to S-Video then back to component inside the old processor chip. This is usually what’s going on in the video system when reviewers proclaim S-Video equal to component video.”

Now I have ‘researched’ this subject more I am of the opinion that this is common practice at the very least. I am also VERY suspicious that some may even process in composite. And you all thought it was simple……

As I said before, buyer beware or at least be educated. It may well be that all the high resolutions signals (component / RGB) get down converted to S Video (or composite?) internally and the differences we see are down to engineering and connectors. Poor old Scart…..The more I look into this subject the worse it gets.

The Snell & Wilcox Zone Plate test pattern on Video Essentials will help people investigate this further if they are as sad as me.

[michaelab]

OK, so SCART may not be that great but in most cases, who cares? As you've mentioned, the advantages of superior systems are often nullified by converting everything down to a lowest common denominator like S-Video or even composite.

It wasn't that long ago that most people were sending RF output from their VCR and/or STB to the TV, and that has to be by far the worst option! Still, most people were happy with it. Common acceptance of SCART has at least made that option almost obsolete.

SCART has the advatage of being very practical in that you can daisy chain devices with it (providing they have 2 sockets as most do these days). It never ceases to amaze me how useful SCART is - everything just 'works' with it.

I'll give you a (rather long) example:

I live in Portugal but I have an old JVC VCR bought in the UK which doesn't support PAL-BG (only PAL-I) so I can't use it as a tuner (coz I'd get no sound). However, I have a Portuguese TV. Both the VCR and the TV only have a single SCART socket so I connected them up. Now, the TV can act as a tuner for the VCR (VCR on AUX (SCART)) with the SCART cable being RGB from TV to VCR and when I play tapes in the VCR, the TV automatically switches to the SCART input and I can see the video, so the SCART cable is now being RGB from VCR to TV.

It gets better, in order to decode premium cable channels I have a decoder box from the cable company which has 2 SCARTs - one goes to the TV, the other to the VCR. Amazingly, the above scenario still works as before and in addition:

When I change channel on the TV to a coded channel, the decoder picks that up and sends decoded output to the TV on the SCART and the TV automatically switches to SCART input, showing the decoded image. Of course if I want to record that decoded channel the SCART from the decoder to the VCR takes care of that.

So, with just 2 SCART cables every imagineable scenario is taken care of and just works, in particular, the TV switching to the SCART input whenever it's relevant. The only thing that doesn't work is if I want to watch one channel and record another but that's the fault of my VCR (not being able to decode PAL-BG) and nothing to do with SCART.

Michael.