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Composite, compoment, s-video, RGB. What's the difference?

Discussion in 'Projectors, Screens & Video Processors' started by samwiley, Oct 16, 2001.

  1. samwiley

    samwiley
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    Back to basics!

    I was wondering if anyone out there could give us beginners a quick overview on the different video connections and which is best?

    Sam
     
  2. Wil

    Wil
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    Yes please,

    I thought I understood them but then I tried to explain them to someone else... :rolleyes:
     
  3. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Oh My God....I am having nightmares of the Event...Yoghurt pots...the heat the heat...

    If no-ones posted a reply by 7.30 ish tonight I'll see what I can do. Gotta fly now though and it's not a 1 minute answer...

    Gordon
     
  4. jrwood

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    I think like me you have the Sony VPL-CX1?, if so I've found that this hooked up to my HTPC gives a far far superior picture when plugged into the D-SUB and not the svideo/composite.

    Also my picture quality is that of my 5 year old Sony FST Trinitron prologic tv (and that blows away my brothers new hitachi widescreen tv for clarity!) :), even the colours look the same when comparing TV on the small screen and large screen thanks to dscaler and the HTPC.
     
  5. Dangerous

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    Hello Sam
    Try this link for an explanation.http://www.michaeldvd.com.au/Articles/VideoConnectors/VideoConnectors.asp
    Regards
    Dave
     
  6. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    This is just a quick overview OK.

    Composite Video: This is a black and white signal with a compressed colour signal encoded along with it. It was designed to be backward compatible with black and white TV system.
    Good points: Takes up limited bandwidth needs only one cable and is, of course, backward compatible with black and white TV systems....
    Bad Points: It's compressed and has limited detail compared to alternatives in both black and white and colour. Extracting the colour info out of the black and white info without creating artefacts is a tricky job (this is what comb filters do)
    Carriers of Composite Video: Laserdisc, Terrestrial TV and Videotape.

    S-Video: This is a form of COMPONENT signal. It is made up of two seperate signals. Y (Black and White) and C (colour). The colour part is still compressed.
    Good Points: Still got less bandwidth than RGB. Carrying the colour and black and white info seperately means they don't have to be extracted from each other at the display end resulting in no artefacts from that process( dot crawl and hanging dots being the usual suspects)
    Bad Points: Not as robust over long distances. Limited colour resolution. Two cables and higher bandwidth than composite
    Sources: Well, I'm not really sure if there are any native s-video encoded formats. Probably s-video tape recordings and that's it. Richard?

    Component: Well, we've already mentioned s-video is component. For this bit we'll talk about YPrPb. It's a three part signal. Black and white info again along with two "colour difference signals". It's an analogue compressed version of the original RGB signal.
    Good Points: Takes up less space than RGB but has, for all intents and purposes, the same picture quality. Greater colour detail than s-video. Less processing required at the display device results in less artefacts
    Bad Points: It's a high bandwidth compared to Composite. Need three cables to send it .
    Sources: DVD's are encoded in component format. DTV is a component format I believe.

    RGB: Well, another version of component signal. This is the full info varient. High bandwidth, all the detail is sent in three colour components. No black and white info in this one.
    Good Points: RGB is the method most display devices use for displaying their info. They mix r/g/b components to create colour. So by feeding them the right info you minimise processing required. Highest quality
    Bad Points: High Bandwidth
    Sources: Don't think there are any native RGB sources.

    Richard Ansell will hopefully come along and correct any things I've forgotten or just got wrong.

    The thing to remember is the format the source signal is in. IE If it's a LASERDISC then you have a composite signal. Some LD players have s-video outputs but that just means they have a comb filter built in. In a case such as that you would be best to compare the s-video out of the LD player with the Composite out being fed to your display device. You may find the comb filter in the display device is better than the one in the LD player resulting in a superior picture even although you are using a "worse" signal output from the player!

    Similarily with DVD the format is component on the disc. Display devices need RGB to work. So at some point that component signal must become RGB. If possible compare RGB and YPbPr outputs on your DVD player to see which gives best picture. You may find the DVD players ability to convert YPBpR to RGB is better than the display device.

    Now off to have my dinner and watch West Wing.

    Hope this helps.

    Gordon
     
  7. lmccauley

    lmccauley
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    You know, the first thing I thought of, when I saw the title of this thread, was yoghurt pots... :D

    Have you thought of putting your and Richard's talk onto a web page? Admitedly it wouldn't be quite as good without seeing the results on the screen, but some good pictures or diagrams could substitute. Before you know it everyone will be talking about the Yoghurt Pot theory of video signals.

    Cheers,
    Liam
     
  8. simoncope

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    Gordon, does this apply to satellite decoders as well - in other words, is the native format of the video signal composite?
     
  9. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Simon,

    I'm not that up to speed with satellite. However, I'd guess that analogue sat was a composite signal (bandwidth issue). Digital is MPEG encoded. MPEG, PAL, NTSC etc are all methods of encoding. With Digital I'd think that the RGB output should be the best and work down.

    Richard Ansell....where are you?

    I'll email him and see if he can come over and enlighten us all!

    Gordon

    edited: Digital Satellite and freeview are MPEG encoded as I said. What comes off the MPEG decoder is Y,Cr,Cb 4:2:2 signal. So component output would be closest to origin. As these boxes don;t have YPrPb usually it means RGB instead. As Richard says below there should be no difference between RGB and YPrPb if they do the matrix transcoding correctly. They won;t though so check S-Video as well just in case......then there's the fact that the display itself might turn an RGB signal in to component or s-video for processing before turning it in to RGB to drive panel/tubes.....nothing is ever simple....
     
  10. samwiley

    samwiley
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    Gordon

    I contacted John Sim after looking at the website and the only RGB/VGA converter he makes is for plasma screens ONLY.

    He told me that when this converter is used with projectors, a cropped image is produced when a PAL signal is fed into it, losing about a 1/3 of the picture. A full image will be reproduced from NTSC sources however.

    The only converter currently available is the RGB/s-video. Do you know if this would produce a significantly better picture than the Pioneer 636D's native s-video output?

    Sam

    [ 17-10-2001: Message edited by: Sam Wiley ]
     
  11. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Hi Sam,

    Sorry I forgot about that. Unsurprisingly John is correct.

    I am unfamilier with your DVD player so can't comment with any authority about whether it'd be any better doing the RGBtoSvideo downconversion inside or outside the player.

    Gordon
     
  12. samwiley

    samwiley
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    Yoghurt pots...mmm sounds intriguing.

    Thanks Gordon, very clear explanation. Also thanks Dangerous, that web page was useful too.

    So my next question...

    My projector doesn't have component input (I know what that means now :)!!) but is it possible to connect the RGB output of my DVD (Pioneer 636) to the projector's D-sub socket, or is that an impossible/pointless thing to do?

    Sam
     
  13. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Sam,

    The RGB out from a DVD player is usually RGB with a sync signal derived from the composite signal.

    The D-TYPE (hd15/vga) socket usually is looking for a RGB signal with seperate horizontal and vertical syns. Often it also is expecting a 32kHz signal rather than the 15kHz interlaced signal from a DVD player.

    So, check what sort of signals are receievable on the D-TYPE. Then , if it wont accept a RGBcomposite sync, go and buy a RGB to VGA level convertor box from John Sim at WWW.RGBTOSVIDEO.CO.UK or .COM not sure which. This little box strips the sync out of the composite and provides a RGBHV signal that most monitors will accept (it doesn't de-iinterlace though). I think they are around £80.

    I will work on the Yoghurt pot story for my web site....I'm sure I supplied Spectre with a pic of the pot in question for the Event article so it may yet become famous!

    Gordon
     
  14. RichardA

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    Hi Everyone,

    Sorry for the delay in jumping in on this thread - busy couple of weeks!

    Basically though I'll agree with Gordon's reply describing the difference between the formats, but if I may I'll add a few extras (and probably end up repeating a lot of Gordon's response as well!).

    Composite - Everything compositedtogether on a single wire. The way the colour is encoded within this signal gives us the terms PAL(europe), NTSC (USA & Japan) and SECAM (France & Russia). These terms have nothing to do with the number of lines or frames per second necessarily, but there is an implication that PAL & SECAM are 625 line 50Hz and NTSC is 525line 60Hz,There are a number of variants, but the only other one we need to worry about in the UK with DVD is PAL-60 - this uses the PAL colour system on a 525 line 60Hz picture to make region 1 DVDs work with the majority of TV sets.This is the native format of analogue TV (satellite and terrestrial), Laser disk players and VHS & 8mm tape.

    S-Video (or Y/C) is the same component parts of Composite video, but the colour and black and white information are separated onto their own wires, this allows full bandwidth detail on the black and white info. There is no good reason why S-Video should be less 'robust' than composite - none of the signal parameters are different - it is usually down to poor drive amplifiers in the source, poor connectors and thin cable!. You will not get S-Video as a native format from any commercial source, only from S-VHS and Hi-8 Camcorders.

    Component (YUV, YPrPb, YCrCb, Y,B-Y,R-Y, YIQ)In this form the colour has been seperated onto two wires (the black and white info is exactly the same as S-Video). As there is no modulation of information within any of signals (unlike Composite and S-Video) there is much less to get wrong in the driving and receiving of the signals. This is the native format of M-PEG and is therefore the format of Digital TV (Satellite and Terrestrial) in standard definition and high definition, DVD and virtually every TV studio in the world (usually over the digital format SDI). There is no implied standard for Component so we should always qualify what we mean, and there are two methods for this - in standard definition TV we generally use the total number of scan lines and the field frequency, so the output from a Region 1 'NTSC' disk over component would be 525/60, from a region 2 'PAL' disk this would be 625/50. When we come to HDTV though we can usually assume the field rate will be 60Hz (actually 59.97) (the only broadcast HDTV rate)and we refer to the number of used scan lines (active lines) and whether it's inlerlaced (i) or Progressive scan (P), so you might see 1080i (1080 scan lines interlace, 60Hz, about 1135 total scan lines)
    YPrPb generally indicates SDTV connection (525 or 625 line) while YCrCb has been hijacked by DVD player manufacturers to indicate a de-interlaced output

    RGB - Also can be refered to as component. The picture information is carried as the seperate primary light colours of Red, Green and Blue, sometimes the Sync (where the picture starts and finishes) can be carried on the Green wire (sync-on-green or RGsB), on it's own single cable (Composite Sync or RGBS) which is the general form on SCART connections, or with two wires, on for Horizontal (line) sync and one for Vertical (frame) sync which is the normal format for computer VGA stuff. Like component there is no specific rates for RGB, it can carry anything from SDTV to UXGA PC rates, generally though for our world RGB generally means Standard Defintion TV while higher resolution we use the VGA type terms or the active resolution (e.g. 1024x768)

    One thing worth noting is that as the native format within the TV industry is YPrPb then there is no difference in colour information between RGB from a DVD player and Component from a DVD player or satellite receiver. Any differences which occur are specifically down to poor matrixing between the formats, not the formats themselves.

    I hope this is of use!

    Richard Ansell
    Snell & Wilcox

    p.s. This whole issue is huge, what we have descibed here is a very condensed version so please don't beat me up over slight simplifications!

    [ 23-10-2001: Message edited by: Richard Ansell ]
     
  15. Cliff

    Cliff
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    It might be worth mentioning the physiological aspects of human vision in this thread. That is, the human eye is very sensitive to the black and white info (luminance) and that is why the colour info (chrominance) in colour TV system (NTSC,PAL etc is a much lower bandwidth. During the early 50's when these TV systems were being developed it was quickly realised that a compromise could be made with the colour and it wasn't necessary to transmit everything at full bandwidth. So even if there hadn't been the compatibility issue with b/w sets RGB transmission would have been unlikely as it would take up unnecessary bandwidth.

    Cliff
     

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