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Simulated process separation, step by step

PrintSeps guides · updated October 2026

Simulated process is how a screen printer gets a photographic or painterly design onto a dark shirt with six to ten standard inks instead of CMYK. Each ink is a halftone that carries one slice of the image; the halftones overlap on press and the eye blends them back into a full-color picture. Here is the whole job, from file to press, in the order a separator actually does it.

What makes it different from CMYK

Four-color process relies on transparent cyan, magenta, yellow and black over white paper. On a black shirt there is no white paper, and plastisol inks are opaque, not transparent. Simulated process gets around both problems: it prints a white underbase first to give the colors something to sit on, and it picks real inks that match the dominant colors of the art (a red, a gold, a royal blue, a flesh tone) so each ink only has to do a little work. A sim-process separation of a sunset might be underbase white, yellow, orange, red, purple, black and highlight white: seven screens, no cyan in sight.

Step 1: Read the art and pick the ink set

Before touching a channel, list the colors that matter. The rule is one ink per family of hue that shows up in a meaningful area, plus black for detail and shadow, plus two whites:

• Underbase white, printed first, under everything that isn't the shirt.
• Highlight white, printed last, only where the art is near-white.
• Black for line work, shadow and the dark end of every tone.
• Three to six colors, one per dominant hue. Pick the vivid, bright version of each: a slightly dark ink can be tinted lighter by the halftone, but a dull ink can never be made vivid.

Six to eight screens covers most art. Ten is the practical ceiling on a manual press; beyond that registration, not separation, is the limit.

Step 2: Build the underbase

The underbase is a grayscale map of "how much white needs to be under this pixel". Fully saturated or dark areas need little or none (let the shirt do the work); light and pastel areas need a lot. Then:

1. Choke it by about half a point to a point so no white peeks out past the color edges. See the underbase choke guide for how much.
2. Drop it under pure black. White under black only makes the black look gray and adds ink to the shirt for nothing.
3. Pull the midtones a little. A base that is too full prints colors that look chalky and flat.

Step 3: Split the color channels

Each color ink gets a plate whose halftone coverage says "how much of this ink here". The classic way is selecting by hue range and feathering the edges so neighboring inks blend instead of butting up; modern separation tools do the same job by assigning every pixel a mix of its nearest inks. Two habits keep the result printable:

• Limit each pixel to two or three inks. Four inks stacked on one dot is mud, and it registers badly.
• Let black carry the darkness. Color plates should hold hue and brightness; the black plate holds shadow and line. If a color plate goes to 100% in the shadows, it will print heavy and lose the detail black would have kept.

Step 4: Halftone everything at one angle

Sim-process plates all use the same screen angle, usually 22.5° (or 61°), rather than the rotated CMYK set. The inks are opaque and sit mostly side by side, and the dot grids line up with each other instead of fighting; a single angle also keeps the dots clear of the mesh threads. Typical frequency is 45–65 LPI, set by mesh count (the LPI vs mesh guide has a table). Use elliptical or round dots, and pull the midtones to compensate for dot gain: a 50% dot on film prints closer to 70% on a shirt.

Step 5: Print order and mesh on press

If the design goes on a light shirt instead, drop both whites, let the shirt be the highlight, and pick the color inks as if they were transparent: the spot vs sim process guide covers when that's the better route.

Common mistakes

• Too many inks. If the preview looks the same with six screens as with nine, print six.
• Underbase under everything. Dark, saturated areas usually look richer with little or no base.
• Mixed angles. Rotating sim-process plates like CMYK invites moiré with the mesh.
• No dot gain pullback. Films that look right on screen print heavy and lose the highlights.