I'm in the ColorSync Utility, on a MacBook Air, looking at the "Phosphor" tab (French MacOS 10.12.6) of the "Color LCD-77E200AD-B0E6..icc" profile. I'm intrigued by the displayed Red, Green, Blue and White chromaticities: x y ------ -------- --------- Red 0.5881 0.3333 Green 0.3229 0.5495 Blue 0.1542 0.0900 White 0.3127 0.3290 White chromaticities are easy to decode, this is straight Rec 709 HDTV D65. However, the red, green and blue chromaticities are not straight Rec 709. As you know, these chromaticities are incomplete without the Y = Luminance factor. Is there a way, mathematically, to compute the Y from the x and y? I'm using Robin Myers's excellent ColorConverter 2.2 to "guestimate" the Y by typing in the x and y values, and trial-and-error different Y factors, until I hit the "maximum" a* and b* for that color, to get at a "realistic" CIE Lab value. Please forgive my technical ignorance. For the red primary, I get the "max" a* with a Y = 55 value which gives a CIE Lab value of 79.04 90.28 54.12. Somehow, this "method" of mine does not make sense? I get a Chroma of 105 and a Hue angle of 31 degrees. Any help is appreciated. / Roger Breton