Spot color separation, free and in your browser

What a spot separation has to get right

A spot separation is one plate per ink, and the rule that matters is that a plate is defined by color, not by shape. A single cream ink might appear in eleven letters of a wordmark, two snowcaps and a scattering of highlights — that is one screen, printed once, so it has to be one plate. Tools that separate by connected region hand you eleven plates and a headache, and tools that filter small regions by area quietly drop the lettering entirely. The separator here clusters in LAB space using perceptual color distance, so inks are grouped the way a printer groups them and small shapes of a known ink stay with their ink.

Ink count, tolerance, and a list you can actually edit

Two controls do most of the work. Ink count sets how many screens you are willing to burn — 2 to 12, and most spot jobs land at 2 to 6. Tolerance decides how far a pixel can drift from an ink before it becomes its own ink, which is what keeps anti-aliased edges and JPEG mush from spawning phantom plates. After that you get a working ink list: merge two near-identical greens that should have been one screen, rename a plate to your actual ink name instead of a hex code, reorder the print sequence, delete a plate you decided to drop, and check each one in per-plate preview before you commit. The nearest PMS match is shown as advice, not gospel — your ink drawer wins.

A real four-color job, separated

Below is an unretouched example: a four-ink retro design on a black garment. Orange, blue, red and cream each landed on their own plate — including the cream lettering and snowcaps, which share a single screen despite being a dozen separate shapes. This came out of the editor you are one click away from; nothing was tidied up for the screenshot.

Free, client-side, and offline

Spot separation runs entirely in your browser. There is no upload, no account, no queue, and no network call at all during separation — which also means it keeps working when the shop internet does not. Export as per-ink transparent PNGs, a numbered ZIP in stacking order, an OpenRaster file for GIMP or Krita, or a layered PSD with one named layer per ink and the selection carried as a real layer mask (three PSD exports a day on the free tier, full quality, never watermarked).

When you want the print math on top

Separation is one half of a press-ready file; the other half is print math. The paid render adds per-ink choke and spread, trapping between adjacent inks, a choked underbase on dark garments, a separate highlight white printed last, dot-gain compensation, registration marks, halftone screening if a plate needs tone, and film output at your chosen DPI. It also writes a multichannel PSD with real spot channels rather than plain layers. That render is 10 credits per image and re-renders are free while you tune, so you can adjust a choke value five times without watching a meter.

Where spot separation is the wrong tool

Spot is for flat and mostly-flat art. Point it at a full-tonal photograph and you will get a posterized approximation, because a photograph does not have discrete inks in it. For photographs you want index separation (posterize plus dither, no halftone angles to worry about) or simulated process (tonal channels, halftoned, underbase, highlight white). Both are one tab away, and both start from the same clustering pass you already ran.