By: Dennis Dunbar, Dennis Dunbar & Assoc.
Dennis Dunbar
When converting images in Photoshop from Color to Black and White there are 2 tools most commonly used, both of these are available as Adjustment Layers: Channel Mixer and Black & White. While the purpose of these tools are similar they work in different ways and can give you very different results. Let’s take a quick look to see what I mean.
Just to keep it simple let’s take a color image that’s already in an RGB space like the one below. Looking at the channels palette in Photoshop you’ll see that this image has 3 channels: Red, Green and Blue. Each of these channels is basically just a grayscale version of the image that controls how much Red, Green or Blue will be in the image. The mix of these channels determines the color, density, and detail of the image, right?
Photoshop’s Channel Mixer Adjustment Layer allows us to interactively change the influence of the Red, Green and Blue channels on our Black & White version. The sliders let us add more Red and take out some Blue pretty easily. To make it easier for us to tell how much we’re adding there are readouts right in the dialogue that tell us what percentage of each channel we’re using. While the general rule of thumb is that we should keep the total percentage to 100%, there’s really nothing preventing you from using whatever you like. It is your image, right?
Here’s an example of this image converted to Black & White using the Channel Mixer Adjustment Layer. (Next to it is a blow up of the Channel Mixer dialogue so you can see the settings I used.)
Note that the adjustments are all based on the individual channels in the image. This can be a pretty powerful tool, but what if I want to get a different rendering, say one that separates the girl from the background a little better? Short of using a lot of the Blue Channel which doesn’t give me really good skin tones I’ll have to resort to selections and masks and more adjustment layers etc.
Now look at this example. Here’s the same image converted to Black & White using the Black & White Adjustment Layer. (Again with a blow up of the dialogue box.)
Since this tool works by adjusting the colors in the image, not by mixing the channels we have a different set of adjustments that let us achieve a much different rendering. Here I added more Red to lighten the subject up a bit while balancing the Yellows and Greens to darken the grassy background. And since her blouse was Purple pushing the Magentas up a bit lightened that up just enough to make her stand out.
You’ll find this tool needs a little experimentation at first to determine what slider will affect what part of the image. With this shot I found the Cyans and Blues sliders had very little effect. But if there was a sky behind her and not the grass it would be a different story.
Keep in mind that the Channel Mixer and the Black & White adjustment layers are simply different tools to keep in your bag of tricks. Neither one is “better” than the other and you probably will find images where one seems to get you where you want to go more easily and vice versa. Just like lenses and filters, the more you play and use them the better you’ll know which to use for what job. Cool thing is, since they’re adjustment layers you can play to your heart’s content.
For a more on converting Color to Black & White just go to my website: http://www.dunbardigital.com and click on the contact me link at the bottom of the page to send me an email.