Originally Posted by TomHuffman
Not just LovingDVD. Cine4Home reported much the same thing as well, though not as explicitly.
The fact that you are new to this is not particularly important. Did you use a white pattern that was the same level of stimulus as the color patterns? Unless you did not, the data is the data. It doesn't change just because the person collecting it hasn't has a lot of experience. The mere fact that both of you report that lowering the green saturation tool has almost no effect on green saturation is, by itself, pretty strong evidence that the CMS has a pretty severe design flaw.
What you guys were finally left with was just lowering the main color control and then trying to compensate for the loss in luma by raising the brightness controls on the various colors, which is at best a kluge. You might want to see if you can get the brightness of green, yellow, and cyan higher without also raising their saturation levels back to where they were.
Cine4Home posted an almost perfect corrected gamut (although without the raw data so it's difficult to know how the Y values were, but I would trust someone like Ekkehart). ColdMachine posted he had no problems following Ekkeharts "hint" to adjust the gamut to perfection. None of those who have "cracked it" have said how they did it exactly, but I believe you stand a better chance to get it right if you are more experienced than me, not from a collecting data point of view (I hope I got that right!), but from a "strategy" point of view. I'm making stabs in the dark, and discovering as I go how the principles work, which is obviously not the bet way to tackle a convoluted CMS like the 750's.
In my last attempt, as I explained, I didn't have at hand the Y percentages for each primary/secondary, so although I did get a better result, it's not a surprise it's still not perfect.
What I mean by strategy is what's the best way to get you from an uncorrected gamut where saturation/hue only can't get you close enough on th x,y space to the best "starting point" to play with saturation/hue before adjusting with brightness. Do you only adjust the color setting? Do you also adjust the tint (which I haven't done in my last attempt as it looked like it was making things worse)? How far down do you push the color? -14 was not enough, so I went all the way to -30 (the maximum) to test the theory, but something in between may allow, after saturation/hue/brightness correction, to get a perfect gamut.
I hope this makes sense. I'm going, this week-end if I can (just caught bad cold!) to try starting from scratch on a new user setting, following exactly the procedure you outline in your very helpful guide, and using the Y percentages you provide to try and get something closer. I'm sure LovingDVD (and others) will try as well, and hopefully we'll get something that's closer...
One question to help me understand what's still wrong in my values: when you say that apart from red, my colors are grossly inaccurate, could you quantify/explain why? Is there something flawed in the theory I am exploring, which is to lower the color value (we still need to find the optimum parameter) to be able to use hue and saturation to bring the colors spot on on the x,y space, and then use the brightness control to compensate for the loss of luminance generated by the lowering of the color control and get Y closer?
If the theory is not flawed, I really believe that it is possible to greatly improve the results (especially if using the correct target Y data as a reference, which I didn't have druing my last attempt, I was just trying to lower dE empirically). If the theory is flawed, then I'm clueless at this stage regarding how to make progress...
Hope this makes some kind of sense. It's hard to argue with your teacher!