Colour Spaces: YUV<->RGB, 601/709 etc.

  • 601/709
      • Usually (video content) is created in RGB, but stored as YCbCr.
      • Upon display it will be converted back again to RGB.
      • This means that two color conversions will take place. The problem is that there are different ways of doing this conversion. If the two color conversions are not the same, the displayed content won’t be the same as the original content.
      • So when converting YCbCr to RGB upon display, the correct color conversion standard (Rec.601 or Rec.709) must be used, namely the one which was used when storing the content.
      • (Rec.709 and Rec.601 are short for ITU-R BT.709 and ITU-R BT.601.)
      • ~ When a Rec.601-encoded YUV is decoded using Rec.709, the picture is more saturated and also red is shifted a bit towards yellow.
      • ~ When a Rec.709-encoded YUV is decoded using Rec.601, the result is a less saturated clip, with red shifting towards magenta and blue shifting to cyan.
  • YUV Color Space
      • Has images showing how increasing Y also changes the colour (which is how I end up with “pizza-faced” people if color curves over-used).
      • …and how some colours become unrepresentable
        • No yellows at low Y
        • No reds or blues at high Y
  • Lab Color Space

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