From Photo to Two-Plate Riso (notes from a work-in-progress)

I’m not chasing CMYK here. Two reasons: (1) it burns through inks and setup, (2) it sands off a lot of what makes Riso feel like Riso. Two plates is a sweet spot for photos — enough tone and mood, still honest about the medium.

I don’t think in ink names while I work. I think in plates:

  • Cool plate → structure / shadows / distance
  • Warm plate → highlights / presence / near-field

Colour choices come later. Files stay monotone all the way through; the only place I write colour is the filename for the studio/tool.

What I actually use

  • Affinity Photo for separations (I prefer owning my tools)
  • Spectrolite for halftoning + overprint preview
  • Uncoated paper (preferably) with a bit of tooth
  • A local studio (for me: If By Magic in Helsinki - find yours on Stencil)

The short version

  1. Decide what the cool plate does and what the warm plate does.
  2. Split the photo into two monotone plates in Affinity: by colour (for colour photos) or tonal range (for B&W).
  3. Preview inks with Recolour / blend overlays per plate (then turn them off before export).
  4. (Optional) add a small trap to the under-plate (≈ 0.25–0.5 mm).
  5. (Optional) Halftone both plates in Spectrolite (pick LPI + angles).
  6. Export 600 dpi plates. Put ink names in filenames only.
  7. Proof 3–5 sheets, tweak per plate, then print the run.

0) Prep the source (boring, essential)

  • Work at final size (300–600 dpi).
  • Clean dust/scratches now — halftones immortalise rubbish.
  • Keep some headroom in shadows/highlights; we’ll shape per plate.

For colour photos: manual colour separation

The goal is two grayscale plates built from different colour regions of your image.

My Affinity process

  1. Duplicate your image twice: name them PLATE_cool and PLATE_warm

  2. Make each plate grayscale-looking (but keep the doc in RGB):

    • Add a Black & White adjustment or Channel Mixer set to Monochrome

  3. Build masks using Select by Colour:

    • Select → Select Sampled Colour
    • Sample the hues you want this plate to carry
    • Adjust tolerance, add more samples
    • With selection active, Cmd/Ctrl+J to copy to new layer inside the plate group
    • Repeat for other colour regions

  4. Shape each plate with Curves and Levels:

    • Cool plate: emphasize structure and lower-mids, protect the top end
    • Warm plate: own the upper-mids and highlights, keep shadows light
    • Constrain outputs to ~8-92% (Levels output: Black 20-30, White 225-235)

Could Spectrolite do the colour split automatically? Yes, and it's decent. But I prefer deciding which objects live on which plate.

For black and white: tonal separation

  1. Duplicate to two plates as before

  2. Use tonal masks:

    • Select → Tonal Range → Shadows/Highlights
    • Or paint masks manually for more control

  3. Cool plate (structure): emphasize 0-70% tones, pull top end down

  4. Warm plate (presence): emphasize 30-100% tones, keep deep shadows lighter

That 30-70% overlap is where the print breathes. If midtones get muddy, reduce the overlap rather than just cranking contrast.

Preview colours without baking them in

Everything stays monotone for export, but you want to see how plates interact:

  1. Group each plate (GROUP_PLATE_cool, GROUP_PLATE_warm)
  2. Add a Recolour adjustment above each group
  3. Pick your intended inks to preview the overprint
  4. Turn these off before export (seriously, I've made this mistake)

Registration drift: add trap

Riso registration varies by 1-2mm. Plan for it:

  • Pick your under-plate (usually the structure/cool plate)
  • Add Layer → New Live Filter → Maximum, radius 1-2px at 300 dpi (≈0.25-0.5mm on paper)
  • Optionally add Minimum (1px) to the top plate to tighten joins
  • You're hiding white slivers, not drawing outlines—keep it subtle

Halftoning in Spectrolite

Export each plate from Affinity as 8-bit grayscale TIFF at 600 dpi, then:

  • Dot shape: Round or elliptical are safe; lines work nice on skies
  • Frequency: 35-45 LPI for photos (coarser = softer, finer = more detail but fussier)
  • Angles: Offset pairs like 15°/75° or 22.5°/82.5° to avoid moiré
  • Use the overprint preview to check balance
  • Export as TIFFs at 600 dpi

Things I’m borrowing from people who do it better

1) Flat-tone layering (threshold / posterise)

Turn parts of a photo into solid shapes instead of dots. One plate can be a thresholded shadow map; the other a mid-tone map. Where they overlap you get a third tone/hue. Looks more like silkscreen; inks look richer because you’re laying flats, not pepper.

2) Stochastic grain or custom textures

Swap tidy dot grids for diffusion dither or bitmap textures. Error-diffusion reads like film grain; custom patterns (stipples, scribbles, scanned paper grain) make tones feel hand-made.

3) Bold-plus-neutral, or no black at all

Pair one neutral plate (for edges/legibility) with one bold plate for mood — or try two colours with no black and let overlap create a “third” tone. Studios focused on photo books (e.g., Outer Space Press) lean into two-ink interpretations, aiming for quality while embracing Riso’s rough, textured character.

4) Design with misregistration

Plan for a 1–2 mm wobble. Put fine linework on one plate; use the other as a forgiving fill so any offset becomes a pleasant halo. Pip Lu (O.OO) frames imperfection as the source of Riso’s personality — treat drift as material, not a bug.

5) Layer order as a creative tool

Dark last usually preserves detail; light last can tint the first pass and feel more “printed.” Test both in proofs; don’t be afraid if the “wrong” order looks more alive. (Spectrolite’s overprint preview helps you pre-judge how layers will mix.)

6) Coarse screens on purpose

Big visible dots (or line screens) can be the aesthetic, not a compromise — especially for skies, seas, concrete, anything that welcomes texture. If you want that look, set a lower LPI or choose halftone shapes accordingly rather than fighting toward smooth CMYK-ish blends.

References & further reading

  • Outer Space Press — on “slow and calculated” Riso for photographic reproduction, embracing texture & imperfections.
  • O.OO — No Magic in Riso — two years of separation experiments; tritone colour charts; design with imperfection.
  • Exploriso — threshold/posterise separations for flat-tone layering.
  • Spectrolite — RISO-ify overview; halftone & dithering guides; practical LPI/angle context.