Originally Posted by Lawguy
This was what I was looking to see. I would be very happy with what you have accomplished. What was your approach?
Now instead of being stuck in New Orleans, I am stuck in Boston but I hopefully will be home tonight and my RS20 awaits.
Well, first of all I got my theory right by re-reading Tom's excellent tutorial. I had used Kal's also excellent "Calibration for dummies" article (it felt at my level!) with success for learning greyscale calibration, so I initially went on with it for my first two color calibration attempts. Unfortunately, Kal doesn't really cover a full CMS and especially doesn't provide the data for the correct percentage of Y for all colors. I my first attempt, I simply ignored Y (sorry!), in my second attempt, I tried empirically to play with brightness to lower dE, and on my third attempt I started from scratch, following religiously Tom's article regarding methodology and data, and using a speadsheet to calculate the right values of Y for primaries and secondaries.
I got the greyscale close enough easily and did not spend too much time refining it, and then I started playing with the CMS.
The trick is to concentrate on green (and yellow) to start with as they are the most far off, set brightness for both to max because you'll probably need it anyway, then lower the color control to bring green within the gamut. The mistake I made in my second attempt was to lower color even more (I went from -14 to -30) and I ended up with not enough brightness to compensate, so I tried to go in the other direction and found a setting closer to Jeff's (I'm -8 and he's -5). Then play with saturation and hue to put it spot on. Don't play with brightness on these two colors (green and yellow) because for some reason it also affects saturation. That's why I went the other way, set brightness to max on these two and tried to find the least damaging value for color to bring them in reach of saturation/hue.
It's then very easy to adjust red. Blue is a bit more tricky because it needs quite a lot of subtle play with hue and saturation to get it right. I wouldn't bother with cyan until blue is adjusted (as well as green). It will stay outside the gamut but you should be able to bring it close enough. Once everything is right on the gamut on the x,y plan, adjust saturation to get Y as close as possible for all remaining primaries and secondaries (I used a spreadsheet for easy calculations). It sounds easy but it requires a lot of back and forthing!
I guess that if I could get a satisfactory result, it proves that anyone should be able to (and no doubt will get even more satisfactory results, especially with cyan)!
I forgot to say that before embarking on my 3rd attempt, I measured the THX preset again in high lamp. Gamut is about the same (not as good as what I got), but greyscale is unfortunately not better. So unless they acounted for an older lamp, the THX preset remains an ok approximation, but I wouldn't live with it because the greyscale is really bad.
Hope it helps...