Hi Graeme, granted that the display behaves at least monotonic, mightn't it be better to search for the brightest WP with the desired chromaticity, subject to the constraints max(R,G,B) = 1, instead determining the clipped WP from a coarse (possibly too inaccurate) model? [ However, there are situations where a WP with max(R,G,B) = 1 may not really be desired. For instance, if the channel response happens to be say monotonically increasing in the 0...0.9 RGB range, but flat (clipped) in the 0.9...1.0 range, then we would rather want leave out the clipped region completely and place the WP at the knee at 0.9, and not at 1.0. Unfortunately that's not just fiction - I have seen this kind of clipped channel response in real life on an LCD display. And I could imagine even more weird behavior of display-internal color corrections. Basically, in order to deal with such flaws, one would need to determine the largest monitonic RGB subset [0..Rmax,0..Gmax,0..Bmax] first, and let the calibration limit the RGB numbers sent to the display to this subset. ] Best Regards, Gerhard Am 23.08.2012 02:24, schrieb Graeme Gill:
János, Tóth F. wrote:Changing the luminance targets to "native" didn't change anyting.No surprise there - the white point needs to be native for the algorithm to be used that targets a dynamic 100% in all channels. A non-native white point targets a calculated white point value. The puzzle is why the target that is computed from the additive model doesn't actually lie close to the gamut surface (ie. doesn't have one channel at 100%). In the previous log you sent me, you'll notice that the clipped value was expected to have an RGB value of 0.886559 0.823500 1.000000 for a white point target of XYZ 83.058731 87.390821 95.159898, but the eventual RGB to meet the white target was 0.9106000 0.8348100 0.9275700. So something is out of kilter with the initial model and the actual device response. It's possible that this is due to the inaccuracies of the rough models device curves. I will change it to just use the matrix to compute the gamut boundary clipping, as this may solve the problem. You can try this out using<http://www.argyllcms.com/disptools.win32.zip> Graeme Gill.