YCbCr: Difference between revisions

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m (YUV moved to YCbCr: common digital video is always YCbCr; YUV is a different codec, which is uses in analog PAL, not in digital video)
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Many modern video codecs rely on a YUV colorspace. 'YUV' is a frustrating acronym since it is so difficult to guess what the letters could possibly stand for. The colorspace was originally known as YC<sub>b</sub>C<sub>r</sub>, with the 'b' and 'r' characters written as subscripts. This is what the components represent:
Many modern video codecs rely on a YCbCr colorspace. The correct written expression for this colorspace is YC<sub>b</sub>C<sub>r</sub>, with the 'b' and 'r' characters as subscripts. This is what the components represent:


* Y = luminance, or intensity
* Y = luminance, or intensity
* U = C<sub>b</sub> = blue chrominance value
* C<sub>b</sub> = "blue chrominance", or more precisely the color deviation from gray on a blue-yellow axis
* V = C<sub>r</sub> = red chrominance value
* C<sub>r</sub> = "red chrominance", or more precisely the color deviation from gray on a red-cyan axis


Where is green represented? Green can be derived from the Y, U, and V values.
Green can be calculated based on these three values.


Note that with most [[RGB]] colorspaces, every single pixel has a different R, G, and B sample. The same is not true with YUV colorspaces. YUV operates on the empirical evidence that the human eye is more sensitive to variations in the intensity of a pixel rather than variations in color. Thus, every pixel in a YUV image has an associated Y sample, but groups of pixels share U and V samples.
YC<sub>b</sub>C<sub>r</sub> is often falsely mixed up with YUV, which is a different colorspace that is not used in digital media but in analog PAL-based stuff as analog TV transmission or analog video tapes.


For information on specific YUV formats, see the [[:Category:YUV Formats|YUV formats category page]].
Note that with most digital [[RGB]] color encodings, every single pixel has a different R, G and B sample. The same is not true with many YC<sub>b</sub>C<sub>r</sub> and also not necessarily true for [[YCoCg|YC<sub>o</sub>C<sub>g</sub>]] color encodings. These YC<sub>b</sub>C<sub>r</sub> variants operate on the empirical evidence that the human eye is more sensitive to variations in the intensity of a pixel rather than variations in color. Thus, every pixel in an image of such a YC<sub>b</sub>C<sub>r</sub> variant has an associated Y sample, but groups of pixels share C<sub>b</sub> and C<sub>r</sub> samples.
 
For information on specific YC<sub>b</sub>C<sub>r</sub> formats, see the [[:Category:YCbCr Formats|YCbCr formats category page]].


[[Category:Compression Theory]]
[[Category:Compression Theory]]

Revision as of 01:22, 17 March 2009

Many modern video codecs rely on a YCbCr colorspace. The correct written expression for this colorspace is YCbCr, with the 'b' and 'r' characters as subscripts. This is what the components represent:

  • Y = luminance, or intensity
  • Cb = "blue chrominance", or more precisely the color deviation from gray on a blue-yellow axis
  • Cr = "red chrominance", or more precisely the color deviation from gray on a red-cyan axis

Green can be calculated based on these three values.

YCbCr is often falsely mixed up with YUV, which is a different colorspace that is not used in digital media but in analog PAL-based stuff as analog TV transmission or analog video tapes.

Note that with most digital RGB color encodings, every single pixel has a different R, G and B sample. The same is not true with many YCbCr and also not necessarily true for YCoCg color encodings. These YCbCr variants operate on the empirical evidence that the human eye is more sensitive to variations in the intensity of a pixel rather than variations in color. Thus, every pixel in an image of such a YCbCr variant has an associated Y sample, but groups of pixels share Cb and Cr samples.

For information on specific YCbCr formats, see the YCbCr formats category page.

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