Halftones: how tone becomes dots

Why dots at all

Ink lays down as a solid film: there is no physical such thing as 50% of a tone. For the eye to see half a tone, you print dots covering half the area — and from a distance they merge into an even tone.

Everything about a halftone follows from that: how many dots per inch, at what angle they sit, and what shape they are.

Line count (LPI)

Line count is how many rows of dots there are per inch. A higher count gives smoother gradients and finer detail, but the dots get smaller, and at some point they stop holding on the mesh.

• 35 LPI. The low end for most shops: one-colour work, heavy white on dark. The most robust, the coarsest detail.
• 45 LPI. The usual choice for simulated process on textiles: clearly more detail than 35 and still stable.
• 55–65 LPI. Needs finer mesh and controlled exposure. Good detail if the process is steady.
• Above 65 LPI. Very fine mesh only; risky on textiles.

These are industry starting points, not a rule. What your mesh and your exposure actually hold is found by testing, and that number is what belongs in the shop profile.

Angles and moiré

In screen printing the moiré that matters is not between inks but between the halftone and the mesh thread. Mesh is stretched at 90°, so a halftone at 0° or 90° lies along the thread and barely prints, while 45° hits the knuckles of the weave and eats detail.

That is why textile shops commonly use the same angle — 22.5° — on every screen: it sits furthest from all of those. Spreading angles between inks is offset and CMYK practice, where there is no mesh at all.

ColorLayers puts every ink at 22.5° by default, for exactly this reason. The angle stays a property of the ink: it appears in the ink map and the report, and any ink can be given its own. A shop printing on paper rather than cloth sets spread angles back in the profile.

Dot shape

A round dot is the most predictable: it grows evenly and joins its neighbours latest. Other shapes change how tone builds through the midrange, and some give a smoother transition in the highlights.

The shape is set per ink, alongside the line count and the angle.

The point where a dot disappears

The lightest areas are the smallest dots, and they are the first to go: they fail to expose, or wash out with the emulsion. On the print it looks like a gradient that stops abruptly.

So before output every film is checked against the minimum dot size in your profile, and anything smaller is marked on the artwork — while there is still time to lift the tone or lower the line count.

Output resolution

Film is written at its own resolution, higher than the artwork’s: a dot needs enough pixels to describe it or its edge turns into steps. 1200 ppi at 55–85 LPI is typical.

It is a separate setting, and it changes nothing about how the artwork looks on screen — only the file that goes to output.

FAQ