Professional Quality Black And White Conversions Using 'Lab' Color And Channels In Photoshop

Written by Steve Patterson, Photoshop Essentials.com

If you've been following along from one tutorial to the next in our look at how to convert color photos to black and white in Photoshop, you've seen how to instantly remove all the color from a photograph by converting it to Grayscale mode. You've seen how to use a Hue/Saturation adjustment layer to easily desaturate all the colors in an image and leave you with black and white. You've seen how to use the Luminosity blend mode on a layer in the Layers palette to hide all the colors in an image, and you've seen how to separate the lightness and color values in a photo by converting it to the Lab color mode. You've also seen how to tweak the final result using either the Multiply or Screen blend mode on a duplicate layer.

Each of these methods of converting a color image to black and white has one serious drawback though, which is that none of them gives you much of anything in the way of control over the result. If you're a professional photographer, chances are you want more control over your images than what these methods offer.

Fortunately, there's a much better way of converting color images to black and white, one that gives you complete control over the process and allows you to customize the black and white conversion to your liking. What is it that gives us this control? Photoshop's Channel Mixer.

Mixing Red, Green and Blue Together

First, let's open up our photo once again, which is currently in the RGB color mode, using red, green and blue to create every color in the image:

Now, with the photo open, let's take a look at the Channels palette:

Since the photo is currently in the RGB color mode, the Channels palette is showing what we'd expect to see, a Red channel, a Green channel, and a Blue channel, with an RGB channel on top which serves as the composite channel, giving us our full color image.

We're going to use all three of these channels (red, green and blue) to create a custom black and white version of the photo, using the Channel Mixer, which, as the name implies, allows us to mix the three channels together until we're satisfied with the results.

If you were following along with your own image and had your Channels palette open, switch back to you Layers palette and click on the "New Fill/Adjustment Layer" icon at the bottom of the Layers palette (the icon which looks like a circle half-filled with black and half with white) to bring up the list of available fill and adjustment layers. Select the "Channel Mixer" adjustment layer from the list.

Selecting "Channel Mixer" from the list will bring up the Channel Mixer dialog box.

In the bottom left corner of the Channel Mixer dialog box is a checkbox next to the word "Monochrome". Click inside the checkbox to select it, which will instantly remove all colors from the image, giving you a black and white version.

Customizing The Result

Here's where the control comes in. We can now customize the look of our black and white image by adjusting how much impact the separate red, green and blue channels have on the image.

By default, Photoshop uses 100% of the information from the red channel to create the black and white version when you click the "Monochrome" option, and leaves the green and blue channels out of it, setting them to 0%. Depending on the photo, this may give you a good black and white conversion, and it does a pretty decent job with my photo here, but usually, this isn't what you want. You'll most likely want to decrease the amount of information from the red channel and add in some information from the green and blue channels in order to get a result you're happy with.

You can continue adjusting the sliders until you get the result you're after, since you're not harming the image in any way.

The 100% Rule

The general rule when converting an image to black and white using the red, green and blue channel slider bars in the Channel Mixer is to try and keep the total value of all three channels adding up to 100%. This will give you the greatest amount of contrast in your image without "blowing out" any of the highlights and losing image detail. Keep in mind though that it may be perfectly acceptable to lose some image detail if the area of the photo you're losing detail in is not the main focus of the image, which means your image may in fact look better to you by increasing the total value of all three channels beyond 100%. Don't blindly limit yourself to the 100% rule. If your image looks better to you even though you've gone beyond 100%, so be it. Let your eyes be the judge, not the numbers.

With my photo, I didn't need to tweak the channel values much in order to get good results. Here's my final black and white image:

I simply reduced my red channel to 92% and bumped the green channel up to 8%, leaving the blue channel alone. Your values will no doubt be different.

And that's our look at using Photoshop's Channel Mixer to convert a color photo to black and white the way the pros do it, giving you complete control over the final result.