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

If you've been following along in order with our tutorials on how to convert color photos to black and white in Photoshop, you've seen how to convert RGB (Red, Green and Blue) images into Grayscale mode, you've seen how to desaturate all the colors in a photo using a Hue/Saturation adjustment layer, and in our last tutorial, you saw how to remove all the colors in an image using the Luminosity Blend Mode in the Layers palette.

In this tutorial, we're going to look at a slightly more advanced and more professional way of converting color images to black and white, yet one that is quite similar to using the Luminosity Blend Mode, since both methods convert the color photo to black and white using the image's luminosity (lightness) values. Rather than using a blend mode this time though, we're going to use the "Lab" color mode.

Once again, I'll use the same photo I've been using in each of these tutorials:

What Is The "Lab" Color Mode?

If you read through our section on converting color images to black and white by converting them to the Grayscale color mode, you'll remember from that tutorial that by default, all color photos and images use what's called the "RGB" color mode, and that the letters "RGB" stand for "Red, Green and Blue". Red, green and blue are the colors of light, and every color our eyes can see is made up of some combination of red, green and blue. Electronic devices which project light, such as your television or computer monitor, use the RGB color mode to display all the colors on the screen. Likewise, devices which capture light, like your scanner or digital camera, capture images in RGB color so they can store all the information about the colors in the image and then pass that information along to your computer monitor so that it can accurately reproduce the colors when it displays the image.

To see what I mean about the photo using red, green, and blue, let's take a look at the Channels palette in Photoshop.

The Channels Palette

By default, the Channels palette is grouped together with both the Layers palette and the Paths palette, which means you'll find it in the same place as your Layers palette. The Layers palette is most likely in the forefront of the group, with the Channels and Paths palettes hiding in the background behind it. To access the Channels palette and send the Layers palette to the background, simply click on the Channels palette's name tab at the top, and it will jump to the front, sending the Layers palette to the back.

As you can see in the Channels palette, with the image in RGB mode, Photoshop separates the image into a red channel, a green channel, and a blue channel, and it uses these three channels to recreate all the colors in our image. The channel at the very top, which says "RGB", is the composite of all three channels, giving us our full color image.

So if "RGB" stands for "Red, Green and Blue", and combinations of red, green and blue create every color our eyes can see, what is the "Lab" color mode, and what does "Lab" stand for? Well, for one thing, "Lab" is pronounced "L-a-b", not "lab", and in case you were wondering, is not short for "Laboratory", although you pretty much do have to be a mad scientist to fully understand how the Lab color mode works. For those of us who are not mad scientists, the only thing we really need to understand is that the Lab color mode separates the lightness values in an image from the colors. The "L" in "Lab" stands for "Lightness". For the record, the letters "a" and "b" actually represent all the colors the human eye can see, with "a" covering all the colors between magenta and green, and "b" representing every color between yellow and blue. And that's all I'm going to say about that because it goes way beyond anything we need for our purposes here. The only letter we're interested in is the "L", since we want access to our photo's lightness values, not the colors.

Converting Our Photo From RGB To Lab

Now that we've had a brief look at what the Lab color mode is, we need to convert our photo to the Lab color mode from RGB. We do that in the same way that we converted a photo to Grayscale mode, by going up to the Image Menu at the top of the screen, selecting "Mode" from the top of the list of options, and then this time, rather than selecting "Grayscale", we select "Lab Color" from the list of available color modes.

You won't notice any changes to your image after you've converted it from RGB to Lab, but let's take a look at the Channels palette now that we've made the change.

Notice that instead of a red, green and blue channel, the Channels palette is showing a "Lightness" channel, an "a" channel and a "b" channel.

Selecting The Lightness Values In The Photo

As I mentioned above, we want to use the lightness values in the image to convert it to black and white. Now that our image is in the Lab color mode, the lightness values are easily accessible to us simply by clicking directly on the Lightness channel in the Channels palette, which will deselect the "a" and "b" color channels and remove the color from the photo.

As soon as you click on the Lightness channel, all the color in the photo disappears.

Convert To Grayscale

We're not quite done yet though. All we've done here is turned off the "a" and "b" color channels in the Channels palette. We need to make sure the color is removed completely, and we need to convert the photo from the Lab color mode back into a more useful color mode, one that most electronic devices can understand, since most won't know what to do with an image that's using Lab color. To remove the color completely from the image and at the same time convert the image into a more useful color mode, all we need to do is convert the image to the Grayscale color mode.

To do that, just go back up to the Image Menu at the top of the screen, select "Mode" once again, and then select "Grayscale".

Let's take one more look at our Channels palette now that we've converted the photo from Lab mode to Grayscale mode.

Images in Grayscale mode contain only one channel, the "Gray" channel, and as our Channels palette is showing, that's exactly what we have. The color in the image has now been completely removed, and the color photo has successfully been converted to black and white.

Multiply And Screen

As we saw in the previous tutorial on converting to black and white using the "Luminosity" blend mode, there's one final step you can take. If you find that your black and white version is too light or too dark, you can duplicate the layer in the Layers palette and then change the Layer Blend Mode of the duplicated layer to "Multiply" if the image is too light, or change it to "Screen" if the image is too dark. You can then reduce the Opacity value of the duplicated layer to adjust the brightness of the image to your liking.

If you need to see exactly how to duplicate the layer and change the blend mode to Multiply or Screen, check out the previous tutorial on converting a color photo to black and white using the Luminosity blend mode.

And that wraps up our look at how to convert a color photo to black and white using the Lab color mode. We have one more way of converting to black and white to look at, and it's the professionals' method of choice since it gives you complete control to create your own custom black and white image using the Channel Mixer. We'll look at that next.