Trimingham looks at one of the more powerful separating options available in Adobe Photoshop.
The tricky part is that you need to set the proper curves to build the quad-tone values that will recreate and separate the image. A simple way to do it is to create a reference point to emulate when creating curves in the quad-tone. The Color Range tool can provide a reference point. You can select several channels in the original image using the Color Range tool—for instance, several shades of gray, a white, and then a black. Then save the channels for recreation in the quad-tone. Now you can then build the quad-tone a-round these selections by recreating one color at a time. Before you produce the final separation, apply the quad-tone to a duplicate grayscale of the original image with the preview turned on to show how things shape up.
The design will more than likely need some manipulation to look good. The curves may benefit from some gentle adjustments to blend properly with one another. If the design looks really good, then it can be split apart and tested quickly. In the design example, I had to modify the gray underbase by adding the white channel information to it. This would allow a bright white to be printed in one step. To do this, hold down the Ctrl/Cmd key, select the channel information in the white, and use it to fill in the areas in the gray underbase channel.
Testing the quad-tone separation set
Now that you’ve completed your first separation set using the quad-tone method, are you staring at the Channels menu, wondering what to do next? The answer is very simple: Just convert your quad-tone image into a multi-channel design by using >Image>Mode>Multi-channel.
It is important at this stage that you copy and paste the channels into alpha channels on the original design for viewing and editing purposes. The original channels in the multi-channel document show them as spot-color channels with no solidity, so they can blend with each other completely. For emulating screen printing, you’re best served by having them as alpha channels with the proper color input in the Channel Options menu.
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