My implementation

[milasudril]

This is what I have come up with. There are some details that needs verification:

1. Y' uses the same coefficients as Y (in XYZ), though Y' is thought of as a gamma-corrected value. I find that strange
2. Should Y'CbCrA use ITU-709 coefficients or other values. Would it be better to choose JPEG values?
3. Is radians appropriate unit for hue.