It's easy to see individual channels in
color in Photoshop's Channels palette--simply select "Color
Channels in Color" in Preferences> Display & Cursors. But what
if you want to print the channels in color, say as samples for
a screenprinter? That takes a few more steps.
Each color channel in an 8-bit CMYK image
is actually a grayscale representation of the image. When you
view a single channel on-screen in Photoshop, it displays, by
default, as gray. The Prefs enable you to display each channel
in color (which generally makes it much more difficult to see
the details of the Cyan and Yellow channels). When two or more
channels are visible in the Channels palette, the display is
always color.
As you can see, when the channels are
displayed in gray and a single channel is visible, it appears
that way both in the palette and in the image window
(upper-left). When channels are displayed in color and a
single channel is visible, it is displayed in its own color
both in the palette and in the image window (upper-right).
Regardless of how the Channels palette is displaying the
channels, when two or more channels are visible, the image
window always displays color (lower samples).
Regardless of whether channels are displayed in grayscale or
in color, an individual channel will always print as
grayscale. The "separations," individual channels printed in
grayscale, are used to make printing plates or screens. The
various levels of gray determine how much of that channel's
ink will be placed on the page in any given spot.
Here's how you can print
color separations in color, and even show the "build" of the
four colors as they are applied:
WARNING: Work on a copy
of your image, not the original.
1. Open a copy of your
artwork in Photoshop. If the image has layers, use the menu
command Layer> Flatten Image. From the Channels palette menu,
choose Split Channels. (NOTE: This command cannot be undone.
However, you can reverse the process with the Channels palette
menu command Merge Channels.)
A separate file is created from each color channel in the
image. The grayscale images show the distribution of each
color throughout the image. In the following image, the
channels have been labeled. The individual file names include
the channel's color after the file extension. Be aware that
this file naming convention can prevent file type recognition
by the operating system. You may need to re-name the files.
2. With the Cyan file active, use the
menu command Image> Mode> Duotone. In the Duotone dialog box,
select Monotone (which uses a single ink). Click the color
swatch to the left to the ink name and define the monotone's
ink as CMYK 100/0/0/0. (You can also select Pantone Process
Cyan from the Custom Colors.)
Using the same procedure, convert the Magenta file to a
Monotone using CMYK 0/100/0/0 and the Yellow file to a
Monotone using CMYK 0/0/100/0. The Black file can be left as
Grayscale.
These images can now be printed
individually, producing color separations printed in their own
colors. (These color separations cannot be used to produce
printing plates.)
3. To show the "build" of color, make the Cyan file active and
use the menu command Image> Duplicate, naming the new file
Cyan-Magenta. Convert the image from Monotone to Multichannel
mode (Image> Mode> Multichannel). In the Channels palette
menu, select the command New Spot Channel. Define the new spot
channel's color as Magenta (CMYK 0/100/0/0) and click OK.
Make the Magenta file active, select all, copy. Return to the
Cyan-Magenta image, make sure the Magenta spot channel is
active, and paste. In the Channels palette, make both channels
visible to see how the two inks will combine.
Duplicate this image, naming it
Cyan-Magenta-Yellow. Add a new spot channel (CMYK 0/0/100/0).
Switch to the Yellow file, select all, copy. Return to the new
composite image, make sure the Yellow channel is active in the
Channels palette, paste.
While you could continue, adding another
spot channel for the Black channel, there's really no need --
that simply duplicates your original CMYK image.
