Right, but where does your black = 0.022 cd/m^2 come from though ?
The only knowledge that collink has about the display is the profile, and any BT.1886 black offset applied has to be chosen to result in a negligible difference between the black the display is capable of, and the black it produces for zero input to the device link.
So from the profile:
xicclu -ff -ir -px basetargets.icm
0.000000 0.000000 0.000000 [RGB] -> Lut -> 0.000000 0.000000 0.000000 [XYZ]
The profile says the display has a perfect zero black. So that's what collink has to work with. To use anything else would result in a raised black when the black point XYZ if inverted.
.022/146.5 = .00015
xicclu -fif -ir -px basetargets.icm
0.000145 0.000150 0.000124 [XYZ] -> Lut -> 0.016065 0.015489 0.013713 [RGB]
which is a result that is likely to be 0.022 cd/m^2 higher than the actual black, which is probably not what you want.
So it doesn't matter what you measure as a black point, it's the black point reckoned by the profile that counts, because that's what's used to predict the RGB values needed to achieve the target.
Now why the profile isn't so accurate at the black point, and whether it matters is a different question. 0.022 cd/m^2 is at or below most instruments accurate capabilities though.
So why doesn't the profile contain my actual measured black point so collink can calculate the desired target response (column 7 above) for everything above black when given the -IB switch? If the profile can't accurately represent my display black point than this will never work properly. One would have to put the desired gamma response into the source profile. Can the switch be modified to accept a user specified black point just for the purpose of calculating the correct above black targets and proceed based on that?
The display pro can reliably measure Y down to 0.005 cd/m^2. I can go back through all my measurements files and and the 0 input value is always 0.025 cd/m^2 +/- a little bit. Achieving the gamma roll-off that the bt.1886 function provides creates a very noticeable improvement for my display in alleviating black crush during daytime viewing which is why I'd like to have it working in the LUT workflow rather than baked into the display calibration. That way I can easily switch from day to night LUTs.
Edited by zoyd - 6/3/13 at 6:55am