ColorLayers
Halftones: how tone becomes dots
A screen can do exactly two things: let ink through or not. Every tone in between exists as dots of different sizes. Halftoning is the conversion that makes them.
Denys Lynnyk, prepress engineer and designer updated
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. Around 160 mesh. The low end for most shops: one-color work, heavy white on dark. The most robust, the coarsest detail.
- 45 LPI. Around 200 mesh. Athletic wear, high-contrast graphics, cheaper shirts: steady and undemanding.
- 55 LPI. 230 to 305 mesh. The middle ground for simulated process and busy artwork, and the value the default profile ships with.
- 65 LPI. 305 mesh and finer, with 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 and appears in the ink map and the report. The scheme itself comes from the shop profile, so a shop printing on paper rather than cloth sets spread angles back there.
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 once in the shop profile and applies to every ink, as the line count does. The angles come from the same profile’s angle scheme.
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
Which line count should I choose?
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Work it out from the mesh: line count is roughly the mesh count divided by 4.5. That puts 160 mesh near 35, 230 near 50 and 305 near 65. Most textile shops stay between 45 and 55, which is why the default profile ships at 55. The final number comes from a test on your own mesh: what matters is not the figure in a handbook but the smallest dot that images reliably in your shop.
Can I print without halftones?
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Yes, if the artwork has no continuous tone, only solid areas. Then every ink prints at full coverage and no dots are needed. Halftones are for gradients and for shades of a single ink.
Where does moiré come from?
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From three places. Most often the halftone coinciding with the mesh thread, which the angle cures it, and 22.5° is the safest. Less often, the halftones of two inks against each other. And separately, a regular pattern in the image itself laid over the halftone, where changing the line count or editing the artwork is what helps.
