Mixing models

• Subtractive — mixes ink colors straight in sRGB, as a linear program. Fastest, and hits almost any color exactly, but it isn't how ink behaves on paper.
• Multiply — treats each ink as a filter built from its published color, so overprinting darkens. Order only matters with press simulation on.
• Kubelka-Munk — models absorption, scattering and fluorescence across 36 wavelength bands. 6 inks are calibrated from measured spectra, the rest inferred from their published color. The most physical of the three, and the only one that handles fluorescent inks.

Press simulation

On by default for Multiply and Kubelka-Munk. Dots spread on absorbent paper — a nominal 50% covers about 75% — while a dot landing on ink already down spreads no further. Calibrated from one photographed chart on one machine, so treat it as approximate on any other. Subtractive is an abstraction rather than a print prediction, so it isn't offered there.

Ink minimization

How much color shift, in ΔE00, you'll accept to drop an ink layer. Zero keeps every color as accurate as the palette allows; higher settings rebuild colors from fewer layers. Offered for Multiply and Kubelka-Munk; Subtractive fits nearly every color exactly and has no spare layers to trade.

Discretizations

Rounds each layer's opacity to a fixed number of steps, for a posterized look.

Print order

Which ink prints first, paper-adjacent. Kubelka-Munk always cares, and Multiply cares once press simulation is on, since a dot spreads differently on paper than on ink already down. Subtractive never does. Choose a fixed order or let Automatic search permutations for the lowest weighted reconstruction error — though where the model ignores order there is nothing to search. It also numbers and names the exported layers, so it still matters there.