How to Decode a Chrominance Value?

[ColecoFan1981]

How does one decode a chrominance value for a certain color like, say, 0.267, if the phase angle of that color is 237 degrees?

 

In other words:

E'_I = gamma corrected I signal

E'_Q = gamma corrected Q signal

I = orange-cyan axis signal, situated 33 degrees ahead of the E_R-E_Y axis.

Q = magenta-green axis signal, situated 33 degrees ahead of the E_B-E_Y axis.

 

In other words, how do I decode a chrominance value (which is equal to the square root of the sum generated from the sum of the squares E'_I and E'_Q) back to its respective I and Q values, which I can then convert to RGB values later?

 

Are there any reliable formulas/matrices out there (such as those devised by Charles Poynton) for which I can do this?

 

Thank you,

 

 

 

Ben

Edited February 4, 2009 by ColecoFan1981

[EricBall]

If you are going to/from RGB you also need the Luma, not just the Chroma phase/saturation. Note: these are NTSC CCIR 601 formulas, ASTC is different.

 

Y = 0.299R' + 0.587G' + 0.114B'

I = 0.596R' - 0.275G' - 0.321B'

Q = 0.212R' - 0.523G' + 0.311B'

 

(All values are gamma corrected.)