YCbCr

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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.

There are different matrix coefficients defined to convert encodings in the RGB color space to YCbCr. Among the more important ones are:

  • ITU BT.601 Used for Standard Definition television signals
  • ITU T.871 JPEG File Interchange Format (JFIF)
  • ITU BT.709 Used for High definition television (HDTV)
  • ITU BT.2020 Used for Ultra high definition television

Others are proprietary or less widely used, such as those defined in Cinepak and SMPTE 240M.

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