Originally Posted by ADU
And just a bit off D65 towards green or yellow-green, as anticipated. (A couple tips on how to compensate for that here
, as mentioned previously.)
Actually, since the CIE xy values are known for the GE daylight CFL bulbs, there's probably a simpler and potentially more reliable way to compensate for the difference in color between them and D65 than just fudging the green setting lower on the display, as described in the link above.
The "error" in the GE bulbs could instead be built into
a special set of tinted or "profiled" grayscale patterns designed to match the color of the GE bulbs on an accurate D65 display. If the "profiled" patterns are used for optical comparison with the GE bulbs instead of regular neutral gray patterns, the result should be more precise D65 grays on the display (without the need to tweak green levels on the display after the fact).
To put it simply, if you match the "tinted" patterns on the display to the color of the GE Daylight bubls, then the neutral grays
on the display should wind up pretty damn close to D65; or at least as close as just about any eyeballing method could possibly allow. By building the difference between D65 and the GE bulbs into the patterns you save yourself the trouble and guesswork of how to tweak the green values lower later on, and also end up with a more accurate result.
Assuming the colors on Joel's graph above are accurate (and they usually seem to be
), then the closest "white" color match to a GE Daylight bulb on a D65 display should be in the neighborhood of R=238, G=255, B=231*
. And the closest 50% gray should be about half that, or around R=119, G=128, B=116*
. (This is in 0-255 "full swing" RGB values, as opposed to 16-235 compressed video levels.)
I haven't done any xyY -> sRGB math to confirm this yet. But in theory, if you use "grayscale" patterns which are based on percentages of the above R=238, G=255, B=231*
white values for optical comparison with the GE bulbs, then the neutral
grays on the display ought to come out pretty close to D65.
For this to work best, you should have a player or other output device (ie, PC with HDMI out) that can output correct color to begin with (which could be a stretch for some players). And the RGB primaries on the display should be as close to the HDTV/Rec. 709 spec as possible. (IOW, a "wide gamut" display should be switched to the "normal gamut" setting, or whichever gamut is closest to Rec. 709, if that's possible.)*Edit: please see updated values in post below.