Dear all,
I want to be sure that what I'm doing is correct. My task is to compute some
theoretical CMYK values that will produce a desired XYZ values from a
printer. These are the steps I'm following:
1 - I printed a set of CMYK patches and measured the XYZ and Lab values with
an x-rite spectrophotometer; for a D50 illuminant. (experimental Lab values)
2 - Then with an IT8 target page, I created a custom ICC profile of my
printer with Monaco Profiler.
3 - I used the profile's AtoB tables to convert the same CMYK values in step
1 to the profile's PCS which is Lab (theoretical lab values).
4 - Then I computed the delta E between the theoretical and experimental Lab
values.
My problem is that I'm getting delta E greater than 10 (for all AtoB tables,
best results with the AtoB1 and AtoB3 tables); which I'm assuming is too
high. The thing is that the media white point is not equal between the
measurements in step 1 and the icc profile in step 3; however the
illuminants are the same. I'm not sure if what I'm getting is correct or if
I'm missing something. I have the following questions:
Should I have to do a Von Kries transformation or XYZ scaling using the
media white point before computing delta E?
Or Do the measured experimental and computed theoretical Lab values are
ready for computing the delta E.
Also, if I'm converting from XYZ to Lab, do I use the illuminant or the
media white point to do the conversion?
What delta E can be considered as acceptable, if we are trying to match a
color spot?
The bottom line is, ( I don't know if I'm asking too much) that I'm not sure
when is necessary to do a chromatic/white point adaptation and what Delta E
to expect between theoretical and experimental results.
Thanks for your help,
Hector
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