YDbDr (Colorspaces VI)

Also an analog colorspace, YDbDr was used in SÉCAM (quentielle ccouleur à mémoire), the French analog TV standard that was also used in Germany, Greece and the Middle east, among others. YDbDr, like the others, use the luminance, Y, and two chrominance components: Db, Dr (for différence bleue and différence rouge).

\begin{bmatrix}  0.299 & 0.587 & 0.114\\  -0.450 & -0.883 & -1.333\\  1.333 & -1.109 & -0.217\\  \end{bmatrix}  \begin{bmatrix}  r\\  g\\  b\\  \end{bmatrix}  =  \begin{bmatrix}  Y\\  D_B\\  D_R\\  \end{bmatrix}

with inverse

\begin{bmatrix}  1 & 0 & 0.526\\  1 & -0.129 & -0.268\\  1 & 0.665 & 0\\  \end{bmatrix}  \begin{bmatrix}  Y\\  D_B\\  D_R\\  \end{bmatrix}  =  \begin{bmatrix}  r\\  g\\  b\\  \end{bmatrix}

What’s unusual with this one is how the chrominance components are scaled. Unlike the other colorspaces we’ve seen so far, this one stretches the two chrominance components quite a bit, giving it a squished appearance. Why? It may be that it buys the scheme some tolerance to the frequency modulation used to encode the chrominance components—but I haven’t found anything on this. In fact, just finding documentation on SÉCAM is hard.

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