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How to make film positives from a PNG

PrintSeps guides · updated September 2026

You have a PNG — a customer logo, a design from an artist, an export from Procreate — and you need film positives your exposure unit can use. Here's the whole path, including the traps that cost shops reprints.

Step 1: Check the resolution before anything else

Film wants 200–300 DPI at print size. A 1000-pixel-wide PNG printed 12 inches wide is 83 DPI — halftones made from it will look like gravel. Divide pixel width by intended print width in inches; if the result is under ~200, ask for bigger art (or expect visible softness). Upscaling in software can rescue borderline art but can't invent detail.

Step 2: Separate the colors

Each ink that will go on press needs its own film. For flat art, that means isolating each color into its own plate (spot color separation); for photorealistic art it means building simulated process channels. This is the skilled step. Your options, roughly in ascending order of automation:

• Manual Photoshop channels — full control, hours of work, expertise required.
• Photoshop actions/plugins (UltraSeps, T-Seps and kin) — faster, still requires Photoshop, a license, and cleanup.
• Automated web tools — upload the PNG, review the proposed plates, adjust, download. Minutes, no installs. (This is what PrintSeps does.)

Step 3: Add halftones deliberately

Any tone that isn't 100% solid must become dots. Three numbers matter:

• LPI (line count): 45–65 LPI for most garment printing. Higher needs finer mesh and tighter process control.
• Angle: a single angle (often 22.5°) for all plates avoids cross-plate moiré in sim process; classic offset angle sets (15/45/75/0) are designed for CMYK, not opaque inks.
• Dot shape: elliptical dots close more gracefully in midtones than round; either beats letting the RIP decide by default.

Compensate for dot gain: a 50% dot on film can print as 65–70% on garment. Good separations pull midtones back so the shirt — not the film — hits the intended tone.

Step 4: Output the films

• Print emulsion-down, right-reading (check your shop's standard — consistency matters more than convention).
• Every film needs registration marks in identical positions, plus a label: plate name, ink, LPI, angle. Unlabeled films breed press-side mistakes.
• Density check: solid black areas on film should block light thoroughly (transmission density ≳3.0). Weak blacks expose through and blur the stencil edge.

Step 5: One-file-per-plate, sanity-checked

Before burning screens, overlay the films on a light table: registration marks aligned, no color hiding in another plate, trap/choke where colors butt, underbase choked 0.5–1 pt so it never peeks out from behind the top colors on dark shirts.

Common questions

Can I make film positives from a JPEG?

Yes — same process. JPEG compression artifacts show up in halftones more than in screen viewing, so high-quality exports matter more than format.

Do I need a RIP?

If your separation tool outputs pre-halftoned films (dots already baked in at your LPI/angle), any accurate printer path works. If it outputs continuous-tone channels, a RIP does the halftoning at print time.

What about transparency in the PNG?

Transparent backgrounds are fine — better than white, since nothing is misread as printable white ink. Just confirm whether white areas in the art are "shirt shows through" or "white ink prints."