I’m working with existing illustrations which consist of only two colours, yellow and black. These were originally created as CMYK TIFFs.

This must be printed on a two-colour press, not CMYK.

The problem I face is that the printer is worried about the trapping of the two colours, i.e. as a result of inevitable paper distortions there may be white gaps between the solid areas of yellow and black. What the printer really wants is for the two colours to be on separate layers, one for yellow the other for black.

In order to achieve this, I could of course just use one of Photoshop’s selection tools to first select the yellow and create a new spot layers from this selection and then do the same for black then just dump the original CMYK layers, however this is not ideal. Whilst Photoshop’s selection tools are good, a lot of the detail will inevitably be lost where it will show up most, around the edges.

Is there any way to collapse a CMYK file into just two spot colours?