Towards Better Chroma Subsampling - SMPTE Presentation Notes
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Chroma Subsampling: How it works

Two things happen:

  1. A color space conversion from R'G'B' to Y', B'-Y', R'-Y' components.
  2. The B'-Y' and R'-Y' components are rescaled smaller and later rescaled to their original size.

#1: The color space conversion:

Video signal is converted into luma and chroma.

Luma approximates the "black and white" portion of the signal.

Chroma approximates the ""color"" portion of the signal.

For Rec. 709 video, the formulas are:

Luma Chroma
Rec. 709 Luma (Y’) = 0.2126 R’ + 0.7152 G’ + 0.0722 B’ B’ – Y’ = B’ – Y’
R’ – Y’ = R’ – Y’

*Throughout this presentation I will gloss over implementation details such as the scale factors and offsets applied to chroma.