On Tue, Jan 5, 2016 at 2:28 PM, Martin Orpen <martin@idea-digital.com> wrote:
I’m not sure what else you’d expect to happen here?
If you build the ICC profile in Argyll using -kz -l300 -L0 you are going to create CMYK with no K and the CMY channels compensating as best they can for the missing K.
That is precisely what happens and what I expected. What I did not expect is: 1. that the resulting separations (by converting with Photoshop using Colorimetric Relative w/BPC) are rendered (in Photoshop, again) so differently than when these same separations are rendered as ISOcoated_v2_eci.icc. Again, the purpose was obtaining separations for the same color space as the profile being used as a source data set, but altering the black generation rule so that no K is used and CMY are compensated to account for that lack. 2. that colors that already were separating using no K when converted to ISOcoated_v2_eci.icc are separated pretty differently when converting to this custom zero-K profile. The purpose was only altering black generation, not separations where black ink was not used already. After having had a look at the data set http://www.color.org/FOGRA39L.txt and the verbose output of colprof, I think the issue (or one of them) is that colprof is assigning the black point that the total ink limit of this profile can produce (300% CMY, with a Luminance value of 23 according to FOGRA39L) instead of that of the profile I am using as a source data set (I don't know the Luminance of the black point of ISOcoated_v2_eci.icc, but 400% CMYK in FOGRA39L purportedly has a Luminance value of 8.71). As a result, when converting to the custom profile using Black Point Compensation, or simply when it is converted to RGB in realtime for on-screen display, the luminance of 300% CMY is brought down to zero instead of where it would fall if rendered as ISOcoated_v2_eci.icc. So I feel I am back at square one: how do I create separations for a color space defined by a profile created from FOGRA39 but using no K and compensating CMY to account for that lack (as far as possible)? That was the original purpose when asking how to create a custom zero-K profile using FOGRA39.