The Photoshop CS2 Book for Digital Photographers [Electronic resources] نسخه متنی

Calculations Method

If there's one dialog in Photoshop that scares the living daylights out of people, it's the Calculations dialog. It's got an awfully intimidating layout for a dialog that simply lets you combine two channels, but that's part of the beauty of itonce you learn this technique, you can "name drop" it to impress other Photoshop users. So the next time you're at a Photoshop party and Deke McClelland strolls by, just casually mention something like: "I was converting this grayscale image using Calculations the other day..." and then see if he offers to buy you a Heineken.

Step One

Open the color photo that you want to convert to grayscale using Calculations. Go under the Image menu and choose Calculations to bring up the Calculations dialog. Basically, what you're going to do here is choose two channels from your color photo that look great when blended together, then you'll use them to create an entirely new photo. For example, if you have one channel that looks too dark and one that looks too light, you can combine the two to create a black-and-white image with lots of depth (at least, that's the theory).

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Step Two

By default, Calculations tries to combine the Red channel (under Source 1) with another copy of the same Red channel (under Source 2). So your job is to experiment to find out which two channels from your color photo look best together, and then find out which blend mode looks best for blending them together. This is easier than it sounds, because you do this by simply choosing channels and blend modes from the pop-up menus. Start by leaving Source 1's Channel pop-up menu set to Red, but change Source 2's Channel pop-up menu to Green and see how that looks.

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Step Three

The default blend mode for Calculations is Multiply, which makes the combination of channels look darker, and that's fine in some situations, but here it makes the photo look too dark. So, change the Blending pop-up menu from Multiply to Overlay. If the tone looks more balanced, but it's too intense, you can lower the Opacity setting (I lowered it to 90% here). Now, just experiment by trying different combinations of channels and blend modes to see what looks best.

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Step Four

When you've come up with a combination that looks good to you, go to the Result pop-up menu at the bottom of the dialog and choose New Document. Click OK in the dialog and a new document will appear with your custom-calculated channel as the Background layer. One last thing: In this new document, go under the Image menu, under Mode, and choose Grayscale.

Regular grayscale conversion

Black-and-white conversion using Calculations