Can you use spot channels in a duotone?

April 4, 2008 12:30 PM

Working with duotones and spot channels in Photoshop question.

I wanted a specific effect for this cover image I'm working with and I'm not sure whether or not my printer is going to kill me for what I'm doing, or whether I need to save the file in a specific way to make it workable.

What I've done is create a duotone (we'll say RED and BLUE colors). I then wanted to highlight two areas — one in the red and one in the blue — so I created additional spot channels for each color and did some touch up coloring.

I now have three channels: pms RED, pms BLUE, and Duotone (made up of the same pms RED & BLUE colors). Is this going to create problems at the printer and how should the file best be saved?

posted by papercake to computers & internet (8 comments total)

Mmm, sounds fishy to me. I'd convert it to a multichannel and make your edits directly to the appropriate channels. I just did a little test and InDesign doesn't see the extra spot channels in the duotone file.

Your printer will probably want an EPS.
posted by Plug Dub In at 1:07 PM on April 4

First, is there a really, really, really good reason you need to use Pantone match colors in your duotone? If not, you will make life easier for everyone if you use simple cmyk mixes.
posted by Thorzdad at 1:07 PM on April 4

"please save it as a CMYK pdf" is probably what the printer will tell you.
posted by joelf at 1:16 PM on April 4

I got the impression that this was a two-color job. If it's four, then by all means CMYK it up.
posted by Plug Dub In at 1:20 PM on April 4

I'll second Plug Dub In here: the printer will probably not handle a three channel file well at all. Make the edits on the respective color channels.

Also: I assumed implicit in the duotone nature of the question we're talking about spot color printing. If it's not two color, who cares?
posted by griffey at 1:42 PM on April 4

Prepress Dept. here.

Your printer won't kill you, but you'll make your prepress operator cry. Converting the whole file to CMYK is one way to get the effect you're looking for, but if you're constrained by a two-color design or a two-color press you'll want a Multichannel DCS 2.0 EPS file.

You already know how to make a multichannel file, so what you'll want to do is split your duotone into two separate channels. Image -> Mode -> Multichannel will split the duotone channels and keep any applied curves. (assuming the curves have been applied in the Duotone Options window) Then you'll want to merge your two Pantone Red channels (Duotone base + highlights) and do the same for your Pantone Blue.

The merging part can be kind of tricky. I've found that copying the individual channels into the layers of a blank PS document, merging, then copying back to the original channel in the original document is the fastest workaround, but that's my particular trick. You may find a way that's easier.

The best way to save the final image is as a Photoshop DCS 2.0 EPS. Make sure that the Spot Colors box is checked, otherwise all that work will be lost. In the DCS 2.0 window, choose your preview type. (I prefer 8-bit tiff because it works best with both Win and Mac) Choose Single File DCS, No Composite from the DCS: drop-down menu. I haven't had to mess with any of the other options in years, so I'd suggest leaving them in the default state.

Speaking for all prepress operators, thank you for asking this question before dropping the file off.
posted by lekvar at 2:34 PM on April 4 [1 favorite]

I should have been clear: this job is limited to two colors. Thanks for all the answers.
posted by papercake at 4:15 PM on April 4

Please, for the love of god and some more prepress tech's sanity, pick up the phone and ask the printer directly next time. Communication is key is making a printing job goes smoothly.
posted by Brandon Blatcher at 8:17 PM on April 4