Here’s a photo I have open in Photoshop. I want to convert this photo to black and white using the Black & White adjustment:
I want to use the adjustment layer version of the Black & White converter, so I’ll click on the New Adjustment Layer icon at the bottom of the Layers palette and choose Black & White from the list of adjustment layers that appears:
This brings up the Black and White dialog box. The main features in the dialog box are the six color sliders, each one controlling one of six primary colors in the image starting with Reds at the top followed in order by Yellows, Greens, Cyans, Blues, and finally Magentas at the bottom:
These sliders adjust how bright or dark each color will appear in the black and white version, and we can use them to emphasize or de-emphasize certain objects or areas in the image, brightening areas we want to bring attention to and darkening less important areas, based entirely on the original color of those areas. Dragging a slider towards the right will brighten areas that contained that color, while dragging a slider to the left will darken areas that contained the color. There’s really nothing more to it than that!
Notice how, when you bring up the Black & White dialog box, each slider is already set to a certain value, with Reds set to 40%, Yellows set to 60%, and so on? These are the default values that Photoshop uses as a starting point for the black and white conversion. You’ll also notice that as soon as you choose the Black & White adjustment from the Layers palette, Photoshop instantly converts your photo to black and white using those default settings. Here’s my image as it appears so far with the default slider values:
The default settings for my black and white conversion are perfect! Or at least, they would be perfect if I wanted the man’s shirt and the girl’s dress to be the main focus of the image. Unfortunately, that’s not really the result I’m going for, but that’s okay because this is just a starting point. I can simply adjust the sliders to make whatever changes I need. To start with, I want the sky above the man’s head to appear a little darker. Now, since I’m looking at the image already converted to black and white, I can’t see what the original color of the sky was, but I know from memory and common sense that the sky was probably blue. So to darken the sky, I simply need to drag the Blues slider in the dialog box towards the left. The further I drag to the left, the darker the sky, as well as anything else in the image that contains blue, will appear. There’s usually a lot of cyan in the sky as well, so I’ll also drag the Cyans slider towards the left. There are no specific values to use here. It depends entirely on your image and the look you’re trying to achieve, so as I drag the sliders, I’ll keep an eye on my image in the document window to make sure I don’t darken the sky too much. Making changes that are too drastic could also introduce banding, giving you ugly, harsh transitions between colors or brightness levels:
After dragging the Blues and Cyans sliders towards the left, the sky in the black and white version of my photo is now a little darker, which helps bring more attention to the main subjects in the foreground. To make it easier to see the changes, I’ve divided the photo into a “Before and After” view, with the default brightness of the sky on the right and the new, slightly darker version on the left:
Depending on the image you’re working with, you may be able to get away with darkening the sky even more. In my case though, if I had tried to darken it any further, I would have ended up with the ugly banding problem I mentioned. Here’s what the sky would have looked like. Notice all the harsh transitions between brightness values, especially where the trees and sky meet? That’s banding. You definitely want to avoid it, so make sure you keep an eye on your image as you drag the sliders:
If you did go too far with a slider, you can undo the last change you made either by going up to the Edit menu at the top of the screen and choosing Undo or, for a faster way, use the keyboard shortcut Ctrl+Z (Win) / Command+Z (Mac). Of course, you can also simply drag the slider itself to undo the change.