Trimingham looks at one of the more powerful separating options available in Adobe Photoshop.
The quad-tone method is good for higher volume shops that have to generate many sets of separations very quickly. The greatest advantage when this style works well is incredible speed. In fact, separations are truly generated in seconds. The downside is that sometimes a fixed method such as this can’t handle the subtleties in image graduations and can simplify and posterize some graphics and make them clunky in transitional areas. Again, base your separation method on the image. Careful observation and execution bring the strengths of this method to the forefront and minimize its weak spots.
The process of creating a quad-tone separation is similar to using the Curves menu to create an image split. The values in the image are converted into specific colors that can then be pulled out as channels.
An easy method of setting up a quad-tone separation set of curves, as a demonstration, is to take a test band of graduating color and then carefully adjust the curves that are input into each color so that they re-present a section of that value range. This set of curves can then be saved and used to separate other images that exhibit the same set of tonal ranges (Figure 1).
The next step, after practicing this system of pulling out colors using the Curves menus on a tonal bar, is to move forward and work on a design. It’s easier to begin with a design in grayscale mode. First, open the image in Photoshop and then convert the image to grayscale and adjust if necessary to make sure the darkest blacks are 100% and the whitest white is 0% (Figure 2).
Next, convert the image into a quad-tone design by using the duo-tone selection, found under >Image>Mode>Duotone. A dialog box opens, and the pull-down menu at the top allows you to select quad-tone. Four colors become available for manipulation as soon as you select quad-tone (Figure 3). A couple of grays, plus a white and a black, can create all of the basic colors that are needed to quickly reproduce a grayscale design.
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