Set to RGB or YCbCr?

Discussion in 'Displays' started by Michael Eriksen, Apr 28, 2007.

  1. Michael Eriksen

    Michael Eriksen Stunt Coordinator

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    I have a sharp 46´ tv connected to my playstation 3 with a HDMI connection.

    The tv is model 46XD1E with a 1080p display. In the HDMI setup i have 3 possibilities

    1) Set to RGB
    2) Set to YCbCr 4:4:4
    3) Set to YCbCr 4:2:2

    I really cant see any difference, but I cant change the setting while im watching an input so its not really easy to compare.

    Which should be the best to choose on the paper ?


    Thanks in advance

    Michael Eriksen
     
  2. ChrisWiggles

    ChrisWiggles Producer

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    On paper it doesn't matter with video sources. Is this the TV option or coming out of the playstation?

    To compare, you want to look at two things: clipping of peak whites and below blacks, and you want to look at color decoding. If the device is sending RGB, it's doing the decoding, if it's sending YCbCr, the display is decoding to RGB. If everything were working properly on both devices, there would not be a difference, but as we all know this can always be a problem. There's some stuff about YCbCr/RGB and color mismatch in the guide linked in my signature as well if you're curious...
     
  3. Michael Eriksen

    Michael Eriksen Stunt Coordinator

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    It is an option in the TV setup. I have no idea which signal the playstation sends via HDMI, since that dosent appear in the manual.
     
  4. Allan Jayne

    Allan Jayne Cinematographer

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    The most important thing is to have both the source and the TV input match. For analog, only the RGB vs. YCbCr (correctly YPbPr) (and the resolution as in 1080i or 480p etc.) must match. For digital (HDMI, etc.) the 4:4:4 etc. must also match or you might not get any picture.

    RGB is the best followed by YCbCr 4:4:4 followed by YCbCr 4:2:2, but if all are 1920x1080 I doubt if you will notice any difference between the first and the third.

    Technically the first two have the same picture detail resolution for a given pixel count, although the number of different color shadings (e.g. from pink to red to blood) of the YCbCr is about half.

    The 4:2:2 has the same nominal or luminance horizontal resolution but half the horizontal resolution in terms of color changes. At normal viewing distances, for 1920x1080 you'll never see the difference between color changes at most 1/1000'th the screen width versus 1/2000'th the screen width.

    Video hints: http://members.aol.com/ajaynejr/vidcolor.htm
     
  5. ChrisWiggles

    ChrisWiggles Producer

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    Well, it communicates with the source what to send if available. You're mainly interested to see that the output is not clipping in whatever setting you choose, and to see that the color decoding is correct. Again, see my guide for more about these two topics.
     
  6. ChrisWiggles

    ChrisWiggles Producer

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    RGB and 4:4:4 are identical in capabilities assuming the source is component to start with. It is true that you lose some capability by going to component, but that has already been at the studio to create the content that you're looking at, so it's a moot point, and in any case the content you're looking at is all 4:2:0, so anything beyond that has capabilities beyond that which is provided by the content. Theoretically as long as each is operating correctly, you would not notice any differences between 4:2:0, 4:2:2, 4:4:4, and RGB(or any others), assuming 4:2:0 video content which is basically everything, unless you are manipulating the video such as for scaling and such.

    Obviously they have to match or the picture you get would be completely messed up, it'd look like an acid trip.
     
  7. Ken Chan

    Ken Chan Producer

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  8. Allan Jayne

    Allan Jayne Cinematographer

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    >>> ... data has a range of ...

    The significance of this is that black level may be different or burying of shadow detail or washing out of highlight detail may be observed. Adjusting the brightness and contrast controls will handle many situations. So long as the source device output format matches (480i, 720p, etc.) the format the TV is expecting, you will still get a steady picture.

    For example if the TV expects values from 0 to 255 and the source material only contains luminance values from 16 to 235, "black" will appear as dark gray.

    A pixel with 24 bits has 8 bits (possible range 0 to 255) for the luminance Y, 8 for the Cr and 8 for the Cb. For 4:2:2 the Cb and Cr are missing from every other pixel and sharing the coloration of the preceding pixel is done.
     
  9. ChrisWiggles

    ChrisWiggles Producer

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    It shouldn't matter whether it's 4:2:0 as to whether or not it's using the video range. I actually am not familiar with PS though, so I do not know what it's doing.
     
  10. Ken Chan

    Ken Chan Producer

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    Sorry, those were two separate issues.

    If the PlayStation is rendering each pixel independently, such that two pixels in a pair could be completely different colors, then taking the resulting frame and outputting that as 4:2:0 would cause a loss of color detail. On the flip side, if it knew it was rendering to 4:2:0, it could do it at 12 bits instead of 8, and provide more color depth.

    As for the video/data range, is it really in the HDMI spec that everything uses 16-235, except for 640x480 RGB? Seems like an odd exception.
     
  11. ChrisWiggles

    ChrisWiggles Producer

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    No, it's not related to the HDMI spec. It is related to the content specs, video content uses video specs, basically ITU 601 or 709 (SD and HD respectively), and both use the same video range which is in 8-bit digital 16-235. Graphics content uses generally sRGB spec which is 0-255, which is used for most computer/internet type content, except for video (ideally). The HDMI spec is just about transferring the data, it doesn't know or care what range is being used HDMI should transmit the whole 0-255 range intact, whether the content is using the video range, the graphics range, or something else entirely.
     
  12. Allan Jayne

    Allan Jayne Cinematographer

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    >>> 4:2:0 which is basically everything

    The 4:2:0 has the Cr and Cb missing from every other pixel on the odd rows and has the Cr and Cb missing from all pixels on the even rows. In order to create 4:2:2 or 4:4:4 bytestream for output, the source device might merely duplicate the Cr and Cb bytes as needed. (RGB requires conversion to 4:4:4 first.) The picture as seen from transmitting this source as 4:4:4 would be indistinguishable from 4:2:2 or RGB.

    Alternatively the source device could do blending resulting in source content "as electronically synthesized 4:2:2 or 4:4:4" (they don't advertise it as such).

    The device converting back to 4:4:4 uses its own coloration formulas and cannot tell whether the Cb and Cr values came from the pixel they were attached to or were already a blend of the pixels they are to be shared with.

    I'm not sure what the Playstation renders.
     
  13. AmusingistheDawn

    AmusingistheDawn Stunt Coordinator

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