Stephan Bourgeois schrieb:
2. why is there more color cast with the colorimeter than the digital camera method? Hypothesis: the colormouse is more accurate and my screen is wrong. But then I shouldn't have a color cast when I print a gray scale.
Just a couple of thougts:
* Did you give the prints enough time to dry? (depending on the used paper and inks, the colors can still change significantly within 24 hours after printing)
* Under which light source do you judge the prints?
* Can you also MEASURE the presence of the color cast with your colorimeter, or can you only SEE it? If you can also measure a significant error, then the profile does not describe your printer's characteristics accurately enough. If you measure only an insignificant deviation (i.e. if the profile is accurate), then either your viewing illuminant or the instrument accuracy are likely the reason for the color cast you can see.
Example how to check:
# find printer RGB for a middle gray patch, L*=50 $ xicclu -ir -fif -pl myprinter.icc 50 0 0 50.000000 0.000000 0.000000 [Lab] -> Lut -> 0.326174 0.428683 0.439484 [RGB]
# Compute absolute L*a*b* for these RGB values. # That's what your colorimeter should read, if # you would print this patch and measure it. $ xicclu -ia -ff -pl myprinter.icc 0.326174 0.428683 0.439484 0.326174 0.428683 0.439484 [RGB] -> Lut -> 44.778623 0.026997 -3.770875 [Lab]
# multiply RGB numbers by 255 # (convert to 0..255 range) $ bc -l 0.326174*255 83.174370 0.428683*255 109.314165 0.439484*255 112.068420
==> print a patch with RGB = [83,109,112] and measure it with the colorimeter (after drying). If the profile describes your printer accurately, then your colorimeter should read L*a*b* = [44.778623, 0.026997, -3.770875]
* You said, that you only used 220 patches to create the profile. This may not be enough to achieve an accurate profile with a good, neutral gray axis. If I resample (fakeread) my printer profile with only 220 full-spread samples, and create a profile from these 220 samples, then then the gray axis of the resampled profile also deviates noticably from my original profile.
If the low number of patches is the reason for the inaccuracy, then you could try to augment your 220 patches with e.g. 100 additional patches along the gray axis, and create a new profile from all 320 patches. You can use "xicclu -ir -fif -pl ..." (see above) to find the RGB numbers for the additional gray axis patches.