Why won't Photoshop limit TAC to 300% when using the ISO Coated v2 300% profile

Question

I have limited hands-on experience in color management (even though I've read quite a bit) and now I have the opportunity to send some posters for offset printing to an online printing company that ask for 8-bit CMYK TIFF files. For these they supply the ISO Coated v2 300% (ECI) profile and ask for a coverage of 300% max.

I created an empty Photoshop document in CMYK with the above profile, but now that I've finished my composition, checking with the eyedropper tool, I realize that the ink coverage exceeds in many places 300% (mostly where the black line-art is).

Isn't this particular profile supposed to be limiting the coverage at 300%? What did I do/understand wrong? What can I do at this point?

Answer 1

If you are asigning the colors directly in CMYK the color profile can not limit the ammount of inks.

If you are mixing layers, for example using multiply, the profile can not limit any ammount of ink.

Basicly the user's input (you) override any value the profile needs to make.

You should not work in Photoshop in CMYK. You should work in RGB and then convert to CMYK as an output file, unless you know exactly how to use CMYK files, filters, blending modes, and how they react.

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Ouch... Thinking of this hurts me... but you can save a copy of the project in RGB and convert it again to CMYK or manually correct the problematic zones.

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Which cases it does limit the amount of inks? Feels strange having an ISO standard with a hard ink-limit that it never enforces!

This is a really nice question.

An RGB color model is quite easy to use and understand, because it is a three dimensional model, you even go left-right, front-back or up-down. We live in a three dimensional universe.

But a CMYK model has 4 components and one of thoose components is just to patch deficiencies on the other 3.

One thing that a color profile does is making the transitions between using just CMY inks to the aditional K seamesly. (the black ink does not start to apearing in a gradient right away, a gradient could start getting darker adding complementary colors first)

Other objetive is making the usage of the model and inks as saturated, contrasted as vivid as possible.

There is not only one way to make the "same" color in a CMYK model. A rough example is a middle gray. You could use c50m50y50 (the real values are not thoose, just as an example) or use k50, or use c25m25y25k25.

So a color profile chooses a color based on the best seamlessly possible way asumming that color is part of an image, an ilustration or photo.

The same with the black. You can have a k100 for texts or an overprinted black shadow over a green solid color c100y100m0k100 but the profile only asumes you have a black starting again from a RGB black. (c75M68y67k90) which is the optimum for that case.

The SWOP profile is a matrix for converting colors from an RGB image to a CMYK, not to override the user's input.