The idea for this quick tutorial came from an article I wrote about converting CMYK images to spot color images with transparency. That article is fairly old but still gets some attention, and a reader wondered how to bring a duotone image into CMYK with proper channel separations. As you might know, by default Photoshop will create CMYK black with a combination of cyan, magenta, yellow and black ink even though the original document (a duotone in this case) uses a plain black ink. You can get around the problem by isolating the duotone channels:
- In Photoshop, make the duotone a monotone by selecting Image â€“> Mode â€“> Duotone… and changing the Type from Duotone to Monotone. This will leave you with only one ink.
- Create a new CMYK file and copy the monotone’s pixel data into one of its channels. If your monotone image displays the black ink, paste it in the black channel.
- In the monotone image, recreate the ink settings for the second color and then convert the image to CMYK. If the second ink is actually a process magenta, cyan or yellow, you can simply copy and paste the pixels into the corresponding CMYK channel.
There is an easier alternative to this method of mode conversion, copying and pasting: make Photoshop understand that black should separate as 100% black ink (plain black) and not a combination of CMYK inks (rich black). Here’s how:
Figure 1: The Color Settings dialog box with the Black Generation drop-down menu set to Maximum.Insert caption here
- Go to Edit â€“> Color Settings…
- Click the CMYK drop-down menu and select Custom CMYK…
- In the Separation Options area, click the Black Generation drop-down menu and select Maximum (see Figure 1). The gray ramp graphic will change to show a single black line (actually, the black line is overlapping the CMY lines).
- Click OK twice to exit Color Settings.
- To convert the duotone to CMYK, just use Image â€“> Mode â€“> CMYK as usual.
That’s all there is to it: Photoshop will now generate as much black in the black channel as possible, which means rich blacks will be interpreted as plain blacks during CMYK conversion. The cool thing about this trick is you can set up a color settings preset to remember this setting, and you can even create an action that changes it at the push of a button. Let’s see the technique in action below on a logo for Imagetek, a digital document storage and management company in Des Moines. This logo works really well for the tutorial because it uses two colors, black and red. I’ve made this a Photoshop duotone graphic with process black and PANTONE Red 032. Standard Photoshop color settings will create the channels seen in Figure 1a: the red is separated into magenta and yellow but the black has been separated and added to all four channels. Figure 1b is what you get after setting the black generation to maximum: the red is separated into magenta and yellow but the black is in its own channel, leaving the cyan blank and the others untouched. This makes work much easier when working with spot color or CMYK printing!
Figures 2a and 2b: The Channels panel show the separations with conventional color settings (left) and with maximum black generation (right).Insert caption here