Martin/Roger/Mike, I believe Roger is correct but he needed to elaborate. I stick my neck out and try. The Total Area Coverage (used to be Total Ink Weight) is the sum of the highest dot percentages in each channel of a CMYK file. These are necessarily customised for a particular printing condition for a host of reasons related to the specific transfer characteristics that result from the combination of ink, substrate, press and printing process. For example, newsprint will support a much lower TAC than sheet-fed coated as it is more absorbent and uses inks with lower tack and viscosity to cope with the run speeds. Laying down 'runnier' inks on 'blotting paper' generates far greater dot gain, or TVI, and is therefore harder to control in the shadows which soon 'plug up' if an inappropriate coated sheet-fed profile was used. Just to complicate the dynamic it is possible to generate and use multiple profiles, with the same TAC, for the same printing condition to produce the same colour space, or gamut. This is one reason why standards-based profiles are continually 'refined' - to achieve a more optimum operation for a given printing condition and its colour space. Using the wrong profile, with a higher TAC, would result in no greater gamut but it would certainly result in more poorly rendered detail, especially in the midtone to shadow region. This means that the Gamut View in Photoshop, which must be comparing Lab coordinates as it describes appearance, is telling you that the colours are out of gamut or beyond the limits of the colour space for a specified printing condition and profile. It does not tell you if that profile is appropriate for the specified printing condition and will not care what the TAC is. It is only concerned with the appearance of the colour. Mark On Fri, Dec 12, 2014 at 11:04 AM, Martin Orpen <martin@idea-digital.com> wrote:
On 11 Dec 2014, at 23:36, Roger Breton <graxx@videotron.ca> wrote:
Mind you, one can never go over the TIL built inside a CMYK output
profile for as long as the image is in RGB space, only at the time of conversion does the R=G=B=0 gets mapped to whatever 300% or 320% or whatever TIL embodied in an output profile.
Which is why it seemed clear that the OP was talking about editing CMYK images…
This has nothing to do with gamut warning, Martin. In my humble knowledge.
Really?
If you edit a CMYK image which has a TAC of 300% and make it 400% Photoshop’s Gamut Warning should show this shouldn’t it?
If you set the soft proof profile to something similar — for example the BasICColor version of ISO Coated v2 (300) while your image is in the usual ICC version it will “kind of” do it.
310% TAC is outside of the limits of the profile. Why doesn’t Photoshop’s gamut warning show this?
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