Color Separation: Methods, Halftones & Screen Printing

Group every pixel into N colour clusters in a perceptual colour space. The user picks N (typically 4–8 for screen printing). Each cluster's colour becomes one ink color; each pixel is assigned to its closest cluster.

Convert continuous gradients into dot patterns. LPI controls dot density (30–65 for textiles); screen angle controls moiré prevention (22.5° + offsets); dot shape controls visual texture (round/square/elliptical).

Map each channel colour to its closest library colour, the one that looks most alike to the eye. Production target: a difference too small to see for a commercial-grade match. Output the colour codes alongside the separated layers as the spec sheet for the print partner.

How many screens you need

One screen per spot colour, plus a screen for any white underbase and any highlight white. A three-colour design on a black shirt is usually four or five screens: the underbase, the three colours, and sometimes a highlight white printed last. Fewer screens means less setup and less to register, so merge colours that read the same at arm's length.

Underbase on dark garments

Inks are slightly transparent, so on a dark shirt the colours sink into the fabric. A white underbase is printed first and flash-cured, and the colours print on top of it. The underbase is choked, made slightly smaller than the colours above it, so no white shows at the edges. On white or light shirts you normally skip it.

Trap and choke

No press registers perfectly. Trapping overlaps neighbouring colours by a hair, so a small shift shows ink rather than a gap of bare shirt. A spread grows a colour outward; a choke pulls it inward. Screen Print Studio applies choke or spread to every screen for you.

Print order

The usual order is underbase, flash, then light colours to dark, with the darkest colour or outline last because it covers small registration errors. A highlight white, if used, goes on at the end. Your printer may change the order for the ink system they run.

Check the films before burning screens

Each separation becomes a film positive: solid, opaque black wherever ink goes. Lay the films on a light table and check that the registration marks line up, that no colour has a stray speck, and that halftone dots are not smaller than your mesh can hold. A rough rule: mesh count about four to five times the halftone LPI, so a 55 LPI halftone wants a mesh around 230. Screen Print Studio exports each screen as a film positive with registration marks.

What is color separation in textile printing?

Color separation is the process of splitting a multi-color design into individual color channels, one channel per ink color in screen printing, or per process color (CMYK) in digital printing. The output is a set of grayscale layers, where each layer's intensity at a pixel determines how much of that color's ink will be applied at that location. Color separation is required before screen printing because each color requires its own physical screen and its own ink pass; the separated layers become the templates for those screens. For digital printing, color profile assignment serves the same conceptual purpose without producing per-color templates.

How does colour separation work?

Colour separation groups the pixels of a design into N colour clusters. The grouping works in a perceptual colour space, calibrated to human vision rather than to how a screen renders colour, so the groups match what the eye sees. The user specifies N (the desired channel count, typically 4 to 8 for screen printing). Each cluster becomes one channel; each pixel takes its cluster's colour. The result is a quantized version of the original design with exactly N colors, plus N grayscale masks defining which pixels belong to which channel.

What is a halftone screen and why is it needed?

A halftone screen converts continuous-tone gradients (smooth color transitions) into a pattern of dots that screen printing can reproduce. Screen printing applies ink in a binary fashion (ink is either on a pixel or off), so smooth gradients are impossible without halftoning. The halftone pattern uses dot size variation to simulate gradient: large dots in dark areas, small dots in light areas, the eye blends them at viewing distance into a continuous tone. Halftone screens have three parameters: LPI (lines per inch, typically 30–65 for screen printing on textiles), screen angle (typically 22.5° for the dominant color, with secondary colors at 45° offsets to avoid moiré), and dot shape (round, square, or elliptical, each with different visual characteristics).

Why match separated colors to a color reference?

A color reference (a colour code with Lab values, or a physical colour standard) is what textile print partners, dye houses and brand specification documents work from. After color separation, each channel's colour should be tied to a color reference so the print partner knows which ink to mix. Texloom's Separation Studio names each channel after its nearest colour in the Texloom colour library. Without a color reference, designers describe colors in RGB or hex, which print partners cannot reproduce reliably because monitors and fabric reflectance differ. Confirm critical colours against the buyer's colour standard before production.

How many colors should a separated design have?

Screen printing typically uses 4 to 8 colors per design. Each color requires a separate screen (an extra cost), and registration becomes harder with more screens (visible misalignment between screens degrades quality). 4 colors is the cost-conscious target for most apparel work; 8 colors is the upper limit for high-end fashion or art prints. Digital roll printing supports unlimited colors so separation is conceptual rather than channel-physical: the digital workflow needs an ICC color profile per fabric base instead. For complex photographic-style designs, designers often use 'process color' (CMYK) which uses overlay of 4 ink colors to simulate the full gamut, but the cost is reduced color accuracy compared to spot-color separation.

Can AI automate color separation?

Yes. AI-augmented color separation groups colours automatically, then applies optimization heuristics to: (1) auto-select the optimal channel count for the design's complexity, (2) prevent visually-jarring color quantization (e.g., choosing channel colours on smooth gradients to minimize banding), (3) auto-assign halftone screen angles to avoid moiré patterns, and (4) name each cluster after its nearest library colour. The designer still reviews and adjusts; AI separation is faster than manual but requires human judgment for high-stakes work.

Do I need an underbase on dark shirts?

Usually, yes. Most plastisol and water-based colours look dull on dark fabric because the shirt shows through the ink. Print a white underbase first, flash-cure it, then print the colours on top. Discharge inks are the exception: they remove the shirt's dye instead of covering it, so many discharge prints need no underbase.

What is the difference between spot color and simulated process separation?

Spot colour separation gives each solid colour its own screen and ink, which suits logos, type and flat artwork. Simulated process builds a photographic image from a handful of spot inks printed as halftones, usually over a white underbase on dark shirts. Four-colour process (CMYK) does the same job with cyan, magenta, yellow and black, and works best on white garments.