Preparing a 1-Bit File for Risograph, From Screen to Press

What does a press-ready risograph file actually look like?

Four things, in the order a shop actually checks them: 1-bit, split into one master per ink color, built at the drum's native 600dpi, and never asking the press for 100% ink coverage across a full sheet. Get those right and the rest of prep is detail work. Miss one and it doesn't matter how good the artwork is — it comes back.

Two mistakes account for most of the bounces. A monitor preview lies about tone, which we'll get to. And files built at screen resolution fail silently the moment they hit a drum built for something else entirely. Fix resolution and tone conversion first. LPI choice, ink density, and multi-color registration all sit downstream of those two.

What resolution should a risograph file be?

600dpi. That's the drum's native resolution, and it's what you design and export at — not a rough target to round toward. Send something below it and the master burns soft, with no fixing it afterward (CCS Imaging Center).

Screen resolution is the trap. Code-based and canvas tools tend to default to a browser-friendly export — p5.riso, for instance, ships images at 72dpi out of the box. That reads fine in a preview and burns visibly soft on a drum (p5.riso getting-started guide). Coming from a generative or code pipeline? Resize to print resolution explicitly before the file leaves your machine. Don't assume the export step already handled it, because it usually hasn't.

Leave a 0.25in blank margin on every edge. Not a design choice — clearance for the press's grip and roller area. Content that runs into it is exactly the kind of thing a shop bounces back before they've even really opened the file.

How do you convert a photo to 1-bit for risograph printing?

A riso driver's "Screen-covered" option is a classic ordered halftone. "Grain Touch" is a randomized error-diffusion dither. Those are the two paths from a continuous-tone photo to the 1-bit output the drum needs, and picking the wrong one for your source is the single most common reason a photo print looks worse than the file did.

Screen-covered gives you two knobs. Screen Frequency sets dot size — higher values mean smaller, finer dots. Screen Angle rotates the dot pattern, and it isn't cosmetic: it's what keeps two or more color passes from beating against each other and producing moiré, a separate problem once you start stacking inks. (See how to stop halftone moiré on riso for the angle math.)

Grain Touch reads more like film grain than a regular dot grid. For photographic source images it's the practitioner default, because the randomization hides press mis-registration and dot gain better than an evenly spaced screen does at the same coarseness (CCS Imaging Center). Prefer to pick a named dithering algorithm directly rather than trust the driver's built-in modes? Floyd-Steinberg vs ordered dithering covers the same tradeoff at the algorithm level.

Quick rule: continuous-tone or photographic source, use error-diffusion. Flat, graphic, or areal art, use ordered halftone — a regular grid reads clean at low detail where a randomized dither just looks noisy for no reason.

What LPI should you use for a riso halftone screen?

Riso drivers expose a screen width range of 38-200 LPI (lines per inch). 71 LPI shows up as a common driver default, but 90-105 LPI is the practical all-round choice most shops reach for first (Exploriso).

Don't guess your way to a number above 105. Move in 5 LPI steps instead — 105, then 110, then 115 — and proof each one. A laser-preview or monitor check simply can't tell you how the paper will absorb ink at that density.

How much ink coverage can a riso press handle?

Not 100%, not across a full sheet. That's a mechanical limit, not a settings preference, and a full-bleed solid at 100% opacity is the single most common reason a file gets bounced back from a shop.

Drop large solid fills to roughly 75-85% opacity instead. The top-center of the sheet is the most vulnerable spot for visible roller marks under heavy coverage — so that's where a too-dark file shows its problems first (RISOTTO Studio advanced setup).

Type and line work have their own floor. Minimum safe text size sits around 7pt; minimum line thickness, around 0.5pt. Fall below that and elements risk dropping out of the stencil entirely, or clogging it during the burn. For fine type or hairlines that genuinely need 100% solid ink — where opacity tricks would leave them looking gray — use a dedicated "Registration black" swatch instead of relying on a layer's fill opacity to get you there.

Why does my print look darker than my screen preview?

Dot gain. Ink spreads as it's absorbed into uncoated paper, so mid-tones on the actual sheet read heavier than the same file did on a monitor or a laser-printer proof (Exploriso).

Paper stock is part of the story. Riso ink is soy or vegetable-oil based, and it needs an uncoated surface to be absorbed and dry — coated stock simply won't cure the same way (Risograph — Wikipedia). If a shop hands you a coated sample sheet to test on, that's the wrong sheet, full stop.

The fix isn't glamorous, but it works: treat any on-screen tone check as approximate, and get a physical proof before committing to a full edition. Especially if you're running near the top of your chosen LPI range, where the margin for error is thinnest.

How do you prepare a file for multi-color riso registration?

Each riso ink color burns its own master and runs as a separate pass through the drum. So a "1-bit file" for a two-color job is really two separate 1-bit files. A four-color job is four. Submit PDF — either pre-separated by color or as flat grayscale layers, one layer per ink — never JPG or PNG, since JPEG compression artifacts on line work in ways a stencil reproduces exactly (Reprographixxx print room guide).

Avoid overprinting small type across passes. Registration between colors is never pixel-perfect, and stacked fine type is where that shows first. Flatten gradients and drop shadows before separating them into layers, too — left un-flattened, they tend to band once they go through a screen. Where two color shapes genuinely need to touch, add trapping: a small deliberate overlap that hides the gap when registration drifts by a fraction of a millimeter, which it always does by some amount.

A pre-flight checklist before you send the file

Copy this into your file-prep notes before export:

• File built and exported at 600dpi, not a screen-resolution default
• 0.25in blank margin on every edge
• Photo source run through error-diffusion (Grain Touch) or ordered halftone (Screen-covered), matched to whether the source is photographic or flat art
• LPI chosen from the 38-200 range, tuned in 5 LPI steps if above 105, test-printed if above 120
• No full-bleed fill at 100% opacity; large solids dropped to 75-85%
• Fine type and hairlines set to a true Registration black swatch, not layer opacity
• One PDF per job, separated by ink color or as flat grayscale layers — no JPG, no PNG
• Trapping added anywhere two color shapes touch
• A physical proof pulled before committing to a full edition

Frequently Asked Questions

Can I send a risograph file as a JPG?

No. Riso shops want PDF, either pre-separated by ink color or as flat grayscale layers, one per pass. JPEG compression introduces artifacting on line work and clean edges, which a stencil burns literally.

What resolution does a riso file need to be?

Match the drum's native 600dpi. Files built at screen resolution (72dpi is a common default from code-based tools) need to be explicitly upres'd before handoff, or the master burns from an under-resolved source and you lose detail you can't get back at the press.

Why does my riso print look darker than my screen preview?

Dot gain. Ink spreads as it's absorbed into uncoated paper, so mid-tones read heavier on the sheet than on a laser-preview or monitor. Treat any on-screen tone check as a rough guide and proof physically before committing an edition.

What LPI should I use for a riso halftone?

90-105 LPI is the practical all-round setting for most jobs. Go coarser (38-60 LPI) for flat gradients and areal art, and only push past 120 LPI on non-photographic art after a test print — gradients break into visible tonal steps at that density.

Can a riso print 100% ink coverage across the whole page?

Not reliably. Full-bleed 100% fill risks paper jams and roller marks, especially top-center. Drop large solid areas to roughly 75-85% opacity, and reserve true 100%-black registration swatches for fine type and hairlines that need to hold their edge.

Run it before you send it

Before the file leaves your machine, run the source image through kott's riso tool and preview the 1-bit conversion — Grain Touch or Screen-covered, LPI, and angle — with the effect already loaded. Seeing the halftone on screen won't catch dot gain. It will catch a resolution or coverage mistake before a shop does.