Editor › Learn › Total Ink Coverage (TAC): The Press Limit Hiding in Your Shadows
What is total ink coverage and why does my printer care?
Total ink coverage (also called total area coverage, TAC) is the sum of the cyan, magenta, yellow and black percentages at any point of the image — up to a theoretical 400%. Real presses cap it, typically around 300% for coated offset work and lower for uncoated stock and newsprint, because paper can only absorb so much ink before it fails to dry, sets off onto the next sheet, or muddies shadow detail. A properly built ICC profile enforces the limit during conversion, which is a core reason to convert with the RIGHT profile rather than any generic one.
Where the limit comes from
Ink is liquid and paper is absorbent — up to a point. Beyond that point, wet ink stacked on wet ink smears in the delivery pile (set-off), dries slowly enough to disrupt finishing, and turns deep shadows into undifferentiated mud. Every printing condition therefore specifies a maximum: characterisation data for coated offset conditions commonly sits around 300–330%, uncoated lower, newsprint in the 220–260% region. The exact figure belongs to the printing condition — your printer's spec sheet or profile is the authority, not a universal rule.
How a profile keeps you legal
You do not manage TAC by hand in raster work. The CMYK profile's separation tables encode it: during RGB→CMYK conversion, black generation (GCR/UCR) replaces overlapping CMY with K so dark neutrals reach depth with less total ink. Convert through a profile whose TAC matches the printing condition and your shadows come out inside the limit automatically. Convert through the wrong profile — say a 340% coated profile for an uncoated job — and every deep shadow in the file may violate the spec, invisibly on screen.
Where violations come from in practice
- Converting with a generic or mismatched profile (the most common source by far).
- Hand-editing CMYK values after conversion — pushing a shadow to C90 M85 Y85 K95 is 355% no profile ever produced.
- Building "rich black" areas with heavy four-colour recipes instead of the printer's recommended build.
- Stacking adjustments on an already-converted CMYK file until channel values creep up.
Checking a file
The reliable check is the one your printer runs: preflight against the job's spec. Short of that, inspect the darkest areas of the converted file plate by plate — a shadow carrying heavy ink on all four plates is the warning sign. In PhotoAIA the Channels panel isolates each plate of a CMYK document; a deep neutral converted through a sane profile shows most of its darkness on the K plate, not four saturated plates stacked.
Try it in PhotoAIA
- Open a photo with deep shadows and convert it with Image ▸ Mode ▸ CMYK.
- Open the Channels panel and view the K plate alone: a good separation carries shadow depth here.
- Cycle the C, M and Y plates and look at the same shadow — through a sane profile they thin out where K takes over.
- Compare a near-black area against pure text black: text should live on the K plate only.
Questions
- Is 400% black the darkest black?
- On paper it is a drying problem, not a darker black. Perceived depth saturates far below 400%; the profile's black generation reaches maximum useful density within the TAC limit.
- Does TAC apply to inkjet and digital presses?
- The physics differs (toner fusing, inkjet ink loads) but analogous limits exist and their profiles encode them the same way. The rule is unchanged: convert with the profile for the actual condition.
- My printer said "max 300%" — what do I actually do?
- Convert with a profile built for that condition (their supplied profile, or a standard one matching it). Do not try to fix TAC by hand-lowering channels after a wrong conversion — reconvert from the RGB master.