Learning to use the Channel Mixer Adjustment Layer
Before the days of the Photo Filter and B&W adjustment layers, Channel Mixer was often used to create a grayscale image that was more expressive than the standard conversion, to tint images, and to create stylized looks for photos. Today Photoshop provides us with easier (though not necessarily better‚ methods to create B&W from color or to tint a grayscale, but it still can create some of the best stylized looks—and much more easily than you might think. It helps to start with the easiest adjustments, though, to get the hang of how the Channel Mixer works.
The Channel Mixer adjustment layer mixes the amount of each channel used to change the hue and brightness of your image. If you’re using it to convert to B&W, it’s straightforward. Simply check Monochrome and you’ll work with the three channels in a single tab—you choose how much of each channel to use, and can get rid of a noisy blue channel altogether by setting it to 0%, while still producing a good monochrome image. To keep the same brightness as the original, the three source channels combined should equal 100%, but you don’t have to make it equal 100% if you want something lighter or darker. If you don’t have a third party plug-in such as Silver Efex Pro or Topaz B&W, the Channel Mixer is still a great way to make better conversions than simply choosing Mode> Grayscale, plus the ability to save presets makes creative B&W’s a one click process.
When you want to play around with color, there’s so much more to do. The Red, Green, and Blue channels in your image are the target, and you adjust each one by mixing together all three channels as your source. For instance, the Red channel’s output can be 100% Red, 0% Green, and 0% Blue, so no change in the target channel from the source. However, you could make the Red slider something less than 100%, and add to it some of the source Green and Blue channels through their sliders, to get quite a different result for the Red Channel alone. Rinse and repeat for the Green and Blue target channels (or for Magenta, Yellow, Black if CMYK). You can even use negative percentages of any source channel to invert it before adding it to the target channel. And just to be really confusing, there’s also a Constant slider. This slider will adjust the brightness of the target channel, with positive values making it lighter, negative darker. and even very slight adjustments have a strong effect on the outcome.
I have always found creating color with the Channel Mixer difficult to predict, and I normally choose another method when tinting a B&W. However, there are two uses for Channel Mixer when working with color that make using it worthwhile. First, if you want to quickly create an old-fashioned B&W hand-tinted or faded print look, add a Channel Mixer adjustment layer, check Monochrome (which converts it to a standard grayscale), then disable Monochrome to add back a bit of color using the sliders. To keep most of the image in grayscale, use just one of the color channels. To make the entire print color, but faded or hand-tinted, use some or all of the channels to adjust the effect until you have a vintage look you like.
To get a good start on creating a look to save as a Color Lookup Table preset, try the Channel Mixer on a color image. Be sure the color image is a flattened Background layer in order to save the adjustments using File> Export> Color Lookup Tables. Then simply play around with the sliders for each target channel to find a nice look for an image. Remember that small changes to each channel will make a significant difference overall. If the photo is typical of many others you take, you’ll be able to stylize your photos simply by adding a Color Lookup adjustment layer.
All in all, the Channel Mixer is still a very versatile adjustment layer. Channels are the source of every image, and being able to target them in this completely non-destructive, re-editable fashion makes this adjustment layer worth taking some time to get comfortable with. If you know exactly how you want to change the color and tone of an image, it’s not usually the first adjustment layer to reach for, but if you’re in the mood to experiment and be open to a little serendipity, Channel Mixer fits the bill.