wet - dry standard and tolerances

postworek

Member
I tried to find the best achievable values for my cmyk inks, using ISO as target. To do this I printed sheet with different densities and measure it using intellitrax. The best dE values after drying I've got were:
Code:
K 1,14
C 2,96
M 0,98
Y 2,11
and I set appropriate Lab values as target in intellitrax software. But I wonder how to correctly interpret ISO tolerances. What if I already have difference in dE more than half tolerance limit? Should I narrow printer tolerance to, for example, +/- 2dE instead of 5? Even so the printer wouldn't know how far from the ISO target he will land because he is printing to some internal standard not ISO targets.

After checking and comparing all measurements I found that the relation between wet and dry L/a/b values is rather constant beside different densities. For example for magenta average difference is:
Code:
L  0,78 with standard deviation 0,06
a -1,21 sd 0,41
b  1,35 sd 0,29.
For black difference is higher but also quite constant
Code:
L  5,18 sd 1,18
a  0,09 sd 0,37
b -0,24 sd 0,51
(whole sheet with other colors is attached below).

If the difference is constant I could calculate a new standard, with ISO target as base, even if in the real world these values are unachievable using particular combination of inks, paper etc. Calculation used (L as example):

correct_wet_standard_L = iso_target_L - (wet_measurement_L - dry measurement_L)

With this values the printer will know, from the beginning, how far he will land from the ISO targets, not some "internal" standard. All this because dE values are constant. Am I correct or there are too many assumptions? I haven't come across such attitude in any program or literature but maybe someone thought about this.

The deltaE relation stays the same regardless drying, it depends on ink characteristics. From the beginning the printer will know, that if he prints something with dE4 wet, the customer will also measure dE4 on dried sheet because they measure from common base (of course they will see different L/a/b values when measuring). The printer also knows, for example, that he cannot achieve dE on magenta below, for example 3, but with "correct_wet_standard" values will also know that he will not exceed dE5 from ISO target, not some internal standard.
 

Attachments

  • dry wet.xls.zip
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