From Duotone to Spot Colour Layers for Riso

[aepasek]

Hi again,

I'm continuing to feel out the prospects of switching from Photoshop to Affinity for risograph printing. One puzzle piece has to do with duotones--a handy way to reproduce images with the limited and eccentric colours of risograph ink.

The way I was taught to do this previously is to take an image and 1) convert it to black and white, 2) use photoshop's Duotone mode, setting the colours to riso inks, 3) convert to 2 channels via multichannel mode, 4) duplicate each channel into a new file, 5) copy/paste the layers from the new files back together in a new document, with multiply set as the blend mode. You end up with a great looking duotone image, with  layers for each colour of ink that you can turn on/off when printing.

So far I've gotten part of the way with Affinity. It seems that the Gradient map adjustment does a good enough job of producing a duotone image from a black and white source (though, if there are more precise ways forward here--count me very interested!). The trick is: how now can I separate out each ink colour into separate layers?

It seems like channel separation for spot colours is a long-standing feature request that hasn't yet been added to the Affinity suite, so I suspect if there's a way forward here, it will be through more unconventional means. Has anyone stumbled into a solution in their travels?

[thomaso]

On 5/3/2022 at 11:16 PM, aepasek said:

how now can I separate out each ink colour into separate layers?

A workaround: Place the object of each Riso colour on a separate artboard, whereas all artboards are a stack of same size & position in the layout window. If I output the document each artboard = each colour will become a separate page.

To avoid the need to untick various colorizing layers I tried a Black & White adjustment on top of the stack which gets used only during output. (it might need a specific setting depending on the used colours & the image source.)

In this sample I used Fill layers (blend mode: Colour) to colorize the grayscale image (blend mode: Multiply). The colour mix is simply set with the blend range curve of the upper (red) layer – no gradient or mask.

–> v1105 riso.afdesign

–>  v1105 riso_b&w.pdf

[aepasek]

Many thanks for this! I've got this to work well in Photo without the artboard, moreover.

I went ahead and recorded a short tutorial, for the benefit of future folks with this question:

 

[MikeW]

Excellent tutorial.