RGB <-> YCbCr  // DDJ #232 july 1995 , american, Page 57.
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  Y  =  0.29900 * R + 0.58700 * G + 0.11400 * B
  Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B
  Cr =  0.50000 * R - 0.41869 * G - 0.08131 * B
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  R = Y + 0.00000 * Cb + 1.40200 * Cr
  G = Y - 0.34414 * Cb - 0.71414 * Cr
  B = Y + 1.77200 * Cb + 0.00000 * Cr
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