Convert varying opacities of a CMYK colour into a spot colour

Question

A project I am working on has all raster/bitmap illustrations in black and orange colours. The orange at full power is 0, 50, 100, 0 CMYK. The artist in some places of the illustration has used lighter opacities of that colour, like 0, 29, 59, 0 and so on.

So, the whole artwork is only using magenta and yellow plates/channels for the colourful bits and black for the outlines.

We want to print this in two colour costing. Previous projects had illustrations in cyan and black colours, which made it very simple cost-wise. Now, I suppose the only option left to make this project 2 colour is to somehow merge the information from magenta and yellow plates into a new spot colour.

The illustrations are in TIFF and they will be placed into InDesign before being exported to PDF.

What are my options? A good workflow for converting channels in Photoshop? Or perhaps some kind of ink mixing in Indesign during export? Or some kind of preflight in Acrobat?

Thank you for any help.

Answer 1

There is a nice easy solution to this which requires no changes to the artwork.

Simply choose an orange Pantone colour. Either agree on a colour that is a close match to any proofs that the customer has seen or just pick a nice, bright orange like 021.

Then, when you send the files to the printer, ask them to use the yellow plate from the process set as the spot orange plate. You’ll get solid colour where the orange is at full strength because it contains 100% yellow and appropriate tints everywhere that the orange is lighter. The black plate is still the black plate.