Process color printing reproduces continuous tone by breaking it into a grid of small dots. The halftone screen. A 50% midtone is half ink, half paper. But ink is not a perfect square pixel: it's a wet droplet that hits substrate and spreads. The spread comes from two sources combined.
Mechanical gain is the physical squashing of ink under press pressure. The plate hits the substrate, the dot deforms outward, and what was supposed to be a 50% dot is now physically larger.
Optical gain is the light-scattering inside the substrate. Light hits a dot, bounces sideways through the paper fiber, and emerges colored from a slightly larger area than the actual ink coverage. A densitometer reads this combined effect as a darker tone than the file specified.
| Substrate | Midtone gain (at 50%) | Standard ICC profile |
|---|---|---|
| Coated paper (gloss/matte) | 12–18% | GRACoL 2013, FOGRA 51, Coated v2 |
| Uncoated paper | 25–30% | FOGRA 47, Uncoated v2 |
| Newsprint | 30–35% | SNAP 2007, ISOnewspaper26v4 |
| Kraft / unbleached | 30–40% | Custom press profile |
| BOPP / PE film | 8–12% | Custom press profile |
| Digital toner (Indigo, Xeikon) | 5–10% | Press-specific G7 profile |
The ICC profile your printer uses has these gain curves baked into it. When the RIP processes a file in the correct profile, it darkens the pre-press dot value just enough that the printed dot lands at the visual tone the designer specified.
For designers working in a color-managed Adobe workflow with the printer's profile assigned, dot gain is invisible. Photoshop and InDesign show a soft proof that already accounts for it, and the RIP compensates automatically on output. You make a 50% gray, you get a 50% gray.
The places it bites are: (1) supplying flat CMYK values for a brand color without realizing those values were measured on a different stock, (2) using a CMYK profile that doesn't match the print process, (3) building rich black or shadow areas that already sit close to the ink limit, then having gain push them past TAC into mud.
If a designed midtone gray is going to print on uncoated kraft, it will look noticeably heavier than the same gray on coated stock from the same press. Even though the file is identical and both jobs are color-managed correctly. This is a substrate reality, not a file error.
An output ICC profile is a calibration of the press: it's measured by printing a test target, reading every patch with a spectrophotometer, and recording how the press distorts color. A 50% file value on this press might print as a 67% measured tone. The profile records that relationship.
When you convert a file through the profile, the conversion runs the relationship backwards: to print a visual 50%, send a 33% dot to the plate. The press then gains it back up to the visual 50% the designer wanted.
This is why "correct ICC profile" is one of the most important file-prep checks a preflight does. Wrong profile → wrong pre-compensation → printed piece is too light, too dark, or has wrong color cast. Right profile → press behavior is invisible to the designer.
Ask your printer for the ICC profile. Every printer has one for every press and substrate combination. Assign it as the working CMYK profile in InDesign or Illustrator. If they say "use GRACoL" or "use SWOP," that's also a profile. Set it.
Soft proof in your design app. View → Proof Setup → Custom → choose the profile. The on-screen preview now simulates what the press will produce, dot gain included.
Don't compensate twice. If you manually lighten the midtones because "uncoated will look dark" and the printer's profile already compensates, your file will print too light. Trust the profile and verify with a printed proof.
Watch your shadows. Heavy shadow values (75–95% on multiple plates) plus dot gain plus high TAC equals a muddy unprintable region. Profile-aware Photoshop curves keep shadows open without losing density.
Preflight reads the embedded ICC profile and flags when it doesn't match the press or stock you've specified.
Check a file →