Halftone generator for screen printing

The four numbers that decide a halftone

Frequency, in lines per inch, is how many rows of dots per inch — garment work typically runs 35 to 65 lpi, and your mesh count sets the ceiling, because a screen physically cannot hold a dot finer than its own openings. Angle is the rotation of the dot grid, and it matters because two grids at similar angles beat against each other and produce moiré. Dot shape — round, elliptical or square — changes how tones join up as they grow; elliptical dots are popular because they avoid the abrupt tonal jump round dots make at 50%. Output DPI is the resolution of the film itself, and 600 or 1200 dpi is what determines how many distinct dot sizes you can actually resolve.

Angles chosen so they do not fight

For four-color process there is a well-established set of mutually non-interfering angles, with yellow placed where the eye notices its pattern least. For simulated process with six, eight or ten inks there is no single canonical set, so the angle assignment is generated for your actual ink count and ordering to keep the plates as far apart as possible. You can override any of it and enter your own angles — some shops have a set they trust on their equipment, and a tool arguing with a printer about their own press is not a useful tool.

Dot gain, the reason process prints go muddy

Ink spreads. A 50% dot on film becomes something well past 50% on fabric, and the effect is worst in the midtones where a print has the most to lose. Dot gain compensation applies an inverse curve before screening, so the dot laid on the shirt lands where you meant it to. The strength is a slider rather than a fixed profile, because gain depends on your mesh, your emulsion thickness, your ink, your squeegee and your substrate. Print a step wedge once on your own setup, read where it actually lands, and set the value — after that, it is the same number for every job on that press.

Grayscale plates or 1-bit film

Most RIPs would rather do their own screening, so continuous-tone grayscale plates are the default output. If you print film directly — through a driver with no RIP, or straight to a laser — switch to pre-halftoned 1-bit output and set your frequency, shape, angles and DPI here instead. A 14-inch plate at 1200 dpi is a 16,800-pixel image, which is a comfortable job for a server and a genuinely painful one for a browser tab; that is the plain reason halftoning is the paid half of the tool.

It comes with the separation, not instead of it

Halftoning is applied per plate as part of the print-ready render, so the same 10 credits that separate the image also screen it: choked underbase, highlight white, choke and spread, trapping, dot gain, halftone, registration marks. Re-renders of the same image are free, so trying 45 lpi against 55 lpi, or round against elliptical, costs nothing but the time to look. If all you need is flat spot plates with no tone, you never need halftoning at all — and that path is free and runs in your browser.

Or skip halftones entirely

Index separation is the escape hatch. Every dot is the same size at 100% ink, tone comes from dot density, and because there are no varying dot sizes there are no angles and no moiré. It is coarser than a good halftone and more graphic in character, but it is far more forgiving on press, and on textured garments and older equipment it frequently wins outright. Index separation is free and runs in your browser.