Component and composite video outputs

Discussion in 'General Electronics Chat' started by electronewb, Aug 15, 2013.

  1. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Is the Y or green in a component video signal full picture and full color? I've been told that for many years that whenever you need composite signal and the device only has component outs to use the Y (green) I tried it today I get full picture but black and white!!
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    I believe you misunderstood. In component video the colors are transmitted as Red, Green and Blue in the RGB model.

    Color TV is transmitted as luminance, phase and chrominance in the YIQ model. The Y signal has the full picture information for black and white. It does not contain color information.
     
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  3. electronewb

    Thread Starter Member

    Apr 24, 2012
    260
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    But in component the green has full picture right?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Not for color. The standard "Component Video" used in consumer electronics is in the YPbPr format. For that the Y (green connector) component contains the luminance (no color) information and the sync signals. The color information is in the Pb and Pr signals. So if you plug only the Y signal into a composite input you will get B & W video, as you observed.
     
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  5. MrChips

    Moderator

    Oct 2, 2009
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    I think what you are missing is the fact that you cannot get something from nothing.
    The color information consists of Red, Green and Blue. You have three unknowns hence you require three equations.

    The RGB signals can be encoded in many different ways, YIQ and YUV are just examples. RGB signals are not compatible with B&W which came before color. To make color compatible with older B&W TV they created the Y (luminance) signal. You still need two more signals in order to decode into RGB.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Perhaps it would further clarify to note that the composite signal has the color information encoded as modulation on a 3.58MHz subcarrier. This subcarrier is not used in component video. That's why there are two other signal cables in the component video to carrier the color info.
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    Is it possible that by "full picture" what was meant is that it contains the sync signals such that, by itself, it forms a valid video signal whereas the others do not?

    Think about it this way -- if all you needed to get full picture and full color was the Y signa, then why would the other two exist in the first place?
     
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