On the Threshold of Photoshop Greatness

Yesterday I was reading an article on TutorialBoard.net on How to Create a Stencil Look in Photoshop. I see this look all the time in ads, especially ones that want to convey artsy overtones, like the Gardner Museum’s After Hours Program. or something you’d see on the Montreal subway.

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You’ll get cleaner results with Illustrator, but Photoshop can get you almost there in much less time.

Anyway, the tutorial is a good reminder of Photoshop’s Threshold command, but as I read it, I was thinking how some images could be quite frustrating to Threshold. Finding just the right spot to divide light from dark may seem impossible….unless you remember that the most powerful adjustments in Photoshop can be performed on individual channels. You’re not limited to working with the composite channel when using Threshold, Curves, etc. Here’s what works on individual channels.

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Why is this important? Take for example, this picture of a fence.

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Say you wanted to include the fence in your stencil look, but not the sky or clouds. With the composite channel this is impossible. By the time you’ve blown out the sky, the fence is gone too.

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But if you isolate the Blue channel (just click on it in the Channels panel)…

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…you can immediately see that the fence and sky occupy two different ranges of values. Then, in the Threshold dialog, it’s a cinch to find the sweet spot.

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Now you need to apply that Thresholded channel to the whole image to work it into your composition. To do that, select the composite channel (again, just click on it at the top of the Channels panel) and choose Image > Apply Image. Then in the Apply Image dialog box, select your Thresholded channel as the source, and apply it using the Normal blend mode.

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Now the whole image is thresholded in a way that you could not achieve by working with the composite channel alone. Obviously, you’ll get the most powerful results from isolating channels on images with saturated colors. The more saturation, the more your channels will differ. Good times.

But wait, there’s more. When I’m struggling with an adjustment in Photoshop, I always remember the sage words of Photoshop authorĀ Dan Margulis, that every image has ten channels. Ten? Really? Yup. R-G-B-C-M-Y-K-L-A-B. By switching modes you can access ten different versions of an image instantly. For example, if you just want to isolate the blackest shadows, you can work with the K channel, Yellows, the Y channel, and so on. Actually, every image has an infinite number of channels, if you consider color profiles, but that is a story for another day.

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