Page 305 - Enhancing CAD Drawings with Photoshop

4386.book Page 289 Monday, November 15, 2004 3:27 PM

REPRODUCING GRAYSCALE IMAGES WITH COLORED INKS 289

Reproducing Grayscale Images with Colored Inks
Anyone who has studied traditional photography is probably aware of the beauty of old-fashioned
photographs. For example, sepia-toned prints have a pleasing antique feel and warmth that is uncom-
mon in computer graphics. You can simulate this effect in Photoshop using Duotone color mode.
In Photoshop, Duotone color mode collectively represents monotone, duotone, tritone, and quad-
tone prints. These terms refer to the practice of printing grayscale images with one- to four-colored inks.
Photoshop does not maintain separate channels for these inks like it does in RGB and CMYK modes.
Instead, the tonal information in duotones come from a single channel containing 256 value levels
only (similar to grayscale). Each ink is allocated a portion of the tonal range in the Duotone Options
dialog box using curves. Let’s take a look at how this works.

1. If you have Farmhouse3.psd open from the previous exercise, you can continue here; if not,
open that file from your hard drive before continuing. This file is also provided on the com-
panion CD if you are jumping in here.
2. Click the Layers palette if it is not already active. Click the triangle button, and select Flatten
Image from the palette menu. Click OK in the warning dialog box to discard hidden layers.

WARNING You cannot convert directly from RGB to Duotone color mode without first converting
to grayscale in order to discard the additional color channels.
3. Choose Image Mode Grayscale. Click OK to the warning dialog box asking whether you
want to discard color information. The black-and-white image was stored with RGB channels
previously, and now it has only one Gray channel carrying the tonal information.
4. Click the Channels palette. Notice that in addition to the Gray channel, special channels still
appear from the previous exercise. Delete the Alpha 1, ObjectID, Normal, and Zdepth channels
by dragging and dropping them on the Trash icon at the bottom of the Channels palette.
5. Choose Image Mode Duotone to open the Duotone Options dialog box. Select Tritone
(three inks) from the Type drop-down list box. Click the Load button to open the Load dialog
box, as shown in Figure 8.39. Navigate through your file system to the Photoshop CS folder
and load the following preset file:

\Presets\Duotones\TRITONE\Process Tritones\BMY sepia 1.ado

Figure 8.39
Loading a set of duotone
options