CMYK separation for screen printing

When CMYK is the right call

Four-color process is the cheapest way to print a full-color photograph, because it is always four screens no matter how complicated the image is. On white or very light garments, and on paper and poster work, it is hard to beat. On dark garments it struggles — process inks are translucent by design, so they need a bright substrate to sit on, and once you add an underbase and start fighting for saturation you are usually better served by simulated process with opaque inks. Knowing which side of that line your job is on is most of the decision.

RGB to CMYK, with the parts that matter exposed

The conversion applies gray component replacement, which is the control that decides how much of a neutral gray is built from equal parts CMY versus replaced by black ink. Heavy GCR uses less colored ink, holds neutrals more stably on press, and is generally kinder to garment printing; light GCR keeps richer colors but makes your grays dependent on three screens registering perfectly. Undercolor removal trims total ink coverage in the darkest areas so you are not laying down four saturated plates on the same spot. Both are exposed rather than baked in, because the right setting depends on your press.

Angles, frequency, and dot gain

Process separation is halftoned at the standard set of mutually non-interfering angles, with yellow placed where it is least visible. Frequency is yours to choose: garment work typically runs 35 to 65 lpi where paper work runs far finer, and mesh count sets your practical ceiling. Dot gain compensation applies an inverse curve so that a 50% dot on your film is closer to a 50% dot on the shirt after the ink spreads — the single largest source of muddy process prints. Output as continuous-tone grayscale plates for a RIP that wants to do its own screening, or pre-halftoned 1-bit film at 600 or 1200 dpi.

What you get back

Four plates — C, M, Y, K — plus registration marks if you want them, a manifest recording the angles and frequency actually used, and a proof rendered over your substrate color. The paid render also writes a multichannel PSD carrying real channels rather than plain layers, so the file behaves like a separation in Photoshop instead of like a stack of pictures. Re-render as many times as you like after adjusting GCR or dot gain; the 10 credits are charged per image, not per render.

Free first, paid when you need film

You can load your artwork, crop it, clean it up, and run a free spot or index separation in the browser without an account or an upload, which is often enough to decide what the job wants. CMYK conversion and halftone screening run on the server because plate rendering at print resolution is not a browser job: 10 credits per image, from a plan at $8.50 a month for 600 credits. No watermarks on any output at any tier.

CMYK versus simulated process, plainly

CMYK: four screens, translucent inks, needs a light substrate, cheapest for complex images, standard and well understood. Simulated process: six to ten screens, opaque inks, works on black, more control and more vivid results, more setup and more judgement. Index sits alongside both as the low-risk option — solid dots, no angles, no moiré. All three are in the same tab and share the same document, so trying the alternative on your file costs you a click.