For any pixel or fill in the file, you add up the four channel percentages. C=80, M=60, Y=50, K=70 → TAC = 260%. The maximum theoretical value is 400% (full ink on every plate). The minimum is 0% (paper white).
The TAC of the file is the maximum value found anywhere in the artwork. A logo region might be at 240%, but if there's one shadow corner of a CMYK image at 320%, the file's effective TAC is 320%, and that's what determines whether the press can hold the job.
| Press | Typical TAC cap | Notes |
|---|---|---|
| Digital toner (HP Indigo, Xeikon) | 240% | Toner can't fuse cleanly above this |
| Flexography (labels, packaging) | 260% | Anilox can't deliver enough wet ink to dry above this |
| Offset (coated stock) | 300% | Sheetfed standard; GRACoL profile assumes this |
| Offset (uncoated stock) | 320% | Absorbent paper holds more wet ink |
| Web offset (publication) | 280% | SWOP standard; faster speeds, less drying time |
| Newsprint | 220% | Very absorbent, very thin paper |
| Flexible packaging (laminate) | 260% | Heavy ink loads cause adhesive bond failure |
These are starting points. Specific presses and substrate combinations may run lower or higher. The press operator and printer's prepress tech will give you the real number.
Set-off. Wet ink transfers from the front of one sheet to the back of the sheet stacked on top of it. The job comes out the back of the press looking fine, then sits in a stack and ruins itself.
Drying failure. The paper or laminate can only absorb so much wet ink. Above TAC, the surface stays wet long enough for downstream press operations, folding, gluing, lamination, to smear or pick the ink off.
Marking through. On thin substrates, heavy TAC areas show through to the back of the sheet as ghosted marks.
Laminate failure on flexpack. Heavy ink in the printed layer prevents the lamination adhesive from bonding properly. The pouch comes off the line looking fine, then delaminates in the customer's hand a month later.
Cracking on creases. Folding cartons and flexpack with heavy TAC at fold lines crack on the bend. The ink layer is thicker than the substrate can flex.
Designers default to "100% black" for solid black areas, then add CMY underneath to make the black look richer. The temptation is to go all the way: 100/100/100/100 = 400% TAC. This is wrong on every press.
Press-safe rich black recipes:
The 100% black plate provides the depth. The supporting CMY just keeps the black from looking thin against any color it sits next to. You don't need a lot of supporting ink to get the visual effect.
In Photoshop: Window → Info, set readout to Total Ink. Sample shadow areas of CMYK images. Anything above the press cap needs reduction.
For images: Image → Adjustments → Curves → CMYK channel mixer. Pull the shadow point of one or more channels down until the densest pixel is under the cap. Channel-by-channel curves work better than a global Levels adjustment because you can keep the black plate at 100 and only reduce the CMY underneath.
For solid fills (rich black, dark backgrounds): rebuild them with the press-safe recipes above.
For overprinted spot colors: if a 100% spot is set to overprint on a region with existing 200% process build, the effective ink in that region is 300%, and the spot still has to dry on top. Either knock out the process under the spot, or reduce the process build.
Preflight samples the densest regions of your file and flags any area where CMYK sum exceeds your press's ink limit.
Check a file →