Printing duotones, About duotones, Convert an image to duotone – Adobe Photoshop CS4 User Manual
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USING PHOTOSHOP CS4
Printing
Last updated 1/10/2010
Printing duotones
About duotones
In Photoshop, duotone refers to monotones, tritones, and quadtones as well as duotones. Monotones are grayscale
images printed with a single, non-black ink. Duotones, tritones, and quadtones are grayscale images printed with two,
three, and four inks. In
these images, colored inks, rather than different shades of gray, are used to reproduce tinted
grays.
Duotones increase the tonal range of a grayscale image. Although a grayscale reproduction can display up to 256 levels
of gray, a printing press can reproduce only about 50 levels of gray per ink. For this reason, a grayscale image printed
with only black ink can look significantly coarser than the same image printed with two, three, or four inks, each
individual ink reproducing up to 50 levels of gray.
Sometimes duotones are printed using a black ink and a gray ink—the black for shadows and the gray for midtones
and highlights. More frequently, duotones are printed using a colored ink for the highlight color. This technique
produces an image with a slight tint and significantly increases the dynamic range of the image. Duotones are ideal for
two-color print jobs with a spot color (such as a PANTONE Color) used for accent.
Because duotones use different color inks to reproduce different gray levels, they are treated in Photoshop as single-
channel, 8-bit, grayscale images. In Duotone mode, you do not have direct access to the individual image channels (as
in RGB, CMYK, and Lab modes). Instead, you manipulate the channels through the curves in the Duotone Options
dialog box.
Convert an image to duotone
1
Convert the image to grayscale by choosing Image > Mode
> Grayscale. Only 8-bit grayscale images can be
converted to duotones.
2
Choose Image > Mode
> Duotone.
3
In the Duotone Options dialog box, select Preview to preview the image.
4
For the Type option, select Monotone, Duotone, Tritone, or Quadtone.
5
Click the color box (the solid square) to open the color picker, then click the Color Libraries button and select an
ink book and color from the dialog box.
Note: To produce fully saturated colors, specify inks in descending order—darkest at the top, lightest at the bottom.
6
Click the curve box next to the color ink box and adjust the duotone curve for each ink color.
7
Set overprint colors, if necessary.
8
Click OK.
To apply a duotone effect to only part of an image, convert the duotone image to Multichannel mode—this converts
the duotone curves to spot channels. You can then erase part of the spot channel for areas that you want printed as
standard grayscale.
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