Dot gain
Halftone dots print larger or look larger than planned, so middle tones come off press darker and muddier than the file.
See it
What it is
Dot gain, formally tone value increase, means a halftone patch prints darker than its nominal file value because the apparent dots grow. Some growth is physical as ink and pressure widen the mark; some is optical as light scatters in the paper around it. The change is usually easiest to see through the midtones.
Press operators measure control patches and use plate or RIP compensation curves to bring the printed tone response back to its target. ICC profiles also describe the characterized result so image separations can anticipate it.
Gotcha: lowering the opacity of the whole image is not dot-gain compensation. Tone value increase varies with stock, ink, plate, screen ruling, and press condition, and absorbent uncoated paper generally shows more than coated stock. Measure the actual process before changing the curve.
Ask AI for it
Measure the 25%, 50%, and 75% halftone control patches with an X-Rite eXact spectrophotometer, calculate tone value increase against the ISO 12647-2 target, and build a RIP compensation curve for each process ink. Reimage the test form, measure it again, and return a before-and-after table for C, M, Y, and K without altering solid 100% patches.