Color Channel Magic

You’ve probably heard the advice that you should always scan in color, even when you’re scanning black and white photos. If not, you heard it here first: always scan in color.

The reason to scan black and white photos in color is that some channels will have more or better information than others. This is especially true if you’re working with old or damaged photos. Let’s look at an example.

You can download it here, if you want to play along at home.

This is a scan of an old photograph and it looks just horrible, doesn’t it? But some color channels are probably less horrible than others. A quick way to check this out in Photoshop is by previewing the color channels. You can do this in a flash with a keyboard hotkey. Press Ctrl+1 (Cmd+1 on the Mac) to preview just the red channel. Ctrl+2 and Ctrl+3 show you the green and blue channels, and Ctrl+~ (tilde) takes you back to RGB mode.

In this scan, the red channel is clearly the best, and the blue channel is the worst. No surprises there; the blue channel will usually be the worst channel.

There are various ways to extract the red channel information into the current or a new document, but my preferred way is by using an adjustment layer. I love adjustment layers! Use them whenever you can. They provide you so much more flexibility now and later by always preserving your original information.

In the Layers palette, click the New Adjustment Layer button at the very bottom, and choose Channel Mixer from the pop-up menu.

I already previewed the channels, so I know that the red channel is the one I want to work with. In the Source Channels area, slide the Red slider to 100%. Leave all the other sliders set to 0. At the bottom of the dialog, check Monochrome on. Monochrome tells Photoshop that we are not building a new Red channel (or green, or blue) but that we want this adjustment layer to affect all three channels equally, to create a grayscale or “black and white” image.
Click OK to close the Channel Mixer dialog.

 

Viola! We’ve easily extracted the red color channel information in just a few seconds without altering our original file at all. It’s not perfect, but it’s a better starting place than we had before, and it’s a better result than anything you’d get by tweaking playing with levels and curves. Now, after we’ve extracted the information from the superior red channel, is when we begin playing with levels and curves.

Notice that I’ve done everything in adjustment layers. I’ve preserved my original scan and all my work thus far. I can go in at any time and make further changes and adjustments, or just start over from scratch.

You might be surprised to find out that this technique can also work for you on color photos. Sometimes.

Here’s a color photo of a boy rolling a hoop.

It’s a fine photo. None of the channels are damaged. But we can get some interesting, and helpful, results by extracting individual color channels and applying their Luminosity onto the original photo. For example, I can create a new Channel Mixer adjustment layer above the photo, set the blue channel to 100% and check Monochrome.

This gives me a perfectly nice black and white photo. In fact, this will often give me a better black and white photo than will simply desaturating the color original, and it’s always a different one. Choice is good. For example, here’s a sea scene made ‘black and white’ by both methods. Red channel extraction is really good at dramatically darkening skies.

But I can go one step further. Back to our boy with a hoop. If I change the blend mode of the adjustment layer to Luminosity, Photoshop uses the tones from our monochrome version as the light and dark values of the original photo, while leaving the colors untouched.

This can sometimes distort a photo surprisingly but the results are usually surprisingly subtle..

I like the way the green channel pumps up the contrast and darkens the red wall.

This photo of a girl in goggles shows much more dramatic results, thanks to the bright green goggles and the red hair. Notice how dark the goggles are with the red channel applied. The red highlights in her hair are also much brighter, and the face almost glows.

This technique can sometimes really help you out with contrast problems and it only takes a minute or two. Try it out and see what happens.

Remember: When in doubt, scan at the highest resolution possible. Always scan in color (even black and white material). Use Adjustment layers, and always save your original scans.