Anders Torger wrote:
With that I expected that for RGB 0,0,0 the calibration curves would also be at 0,0,0, but looking at the calibration curves in the .cal file I see: I R G B 0.0000 0.023793 0.020968 0.020392 That is non-zero for the black point, and also slightly different values for RGB, so desipte that -k is 0.0 there seems to be black point correction. Is this the expected behaviour, or am I doing something wrong?
Notice that these are device values. The device response could be almost anything, so how do you know that the above produces something other than black ?
It seems like the -A parameter can control when calibration is reduced, but I expected that with -k 0.0 the curves will always end at 0,0,0. Could it be that the gamma setting affects the process?
No, it is expected if the display response has a flat spot at zero. Because the calibration curve is composed of finite steps, it can't instantaneously transition from zero to what it needs to be to start displaying something (ie. the inverse of flat is an infinite slope step). So to make the transition smooth and the response progressive, the zero is a device level that is as large as possible and has a color that (hopefully) is the same as black. Graeme Gill.