Sign & Digital Graphics

January '17

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S I G N & D I G I T A L G R A P H I C S • January 2017 • 41 A better technique is to first convert the image to grayscale, and then con- vert it back to RGB. The image can then be posterized to the specific number of shades of gray. Each value of gray can be selected and then filled with the unique color. This effect simulates a multicol- ored serigraph (a type of screen-printed print). Here is a detailed step-by-step illus- trated workflow of the process (as shown in Figure 6): Open a full color RGB image (see Figure 6a). Choose Image > Mode > Grayscale to convert the image to 256 gray values (see Figure 6b) Click the Posterize icon in the Adjustments panel and enter a Levels value of 4—you can enter any amount from 2 to 255 (see Figure 6c) Click OK. Notice that the image is now divided into four shades of gray: white, light gray, dark gray, and black (see Figure 6d) Choose Image >Mode > RGB to convert the image back to RGB. Make a new layer and place it at the top of the stack. Name it "Color." From the Tools panel, choose the Magic Wand tool. In the Options bar set the Tolerance to 1; clear the Anti-Aliased and Contiguous options and choose Sample All Layers. Click an area of white to select all of the white in the image. Choose Window > Show Swatches. Pick a light color from the Swatches panel. Target the Color layer and press Option + Delete (Mac) or Alt + Backspace (Windows) to fill the selected area with the color (see Figure 6e). Repeat the process for each of the additional shades of gray choosing a cor- respondingly darker color for each shade (see Figure 6f). Figure 6a: Open a full color RGB image. Figure 6b: Choose Image > Mode > Grayscale to convert the image to 256 gray values. Figure 6c: Click the Posterize icon in the Adjustments panel and enter a Levels value of 4 (you can enter any amount from 2 to 255). Figure 6d: Click OK. Notice that the image is now divided into four shades of gray: white, light gray, dark gray, and black. Figure 6e: Choose Window > Show Swatches. Pick a light color from the Swatches panel. Target the color layer and press Option + Delete (Mac) or Alt + Backspace (Windows) to fill the selected area with the color. Figure 6f: Repeat the process for each of the additional shades of gray choosing a correspondingly darker color for each shade. Figure 6

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