The purpose of this tool is self-evident although it is something of a misnomer. Monochrome would be a better term as it also allows you to tone your image with any other single colour. Photoshop offers several ways to convert to monochrome. Some, like desaturation and converting the mode to greyscale are to be avoided as they give no control over the conversion. Using a Black and White adjustment layer is nearly always my preferred option as it gives lots of control over how your image is converted. It is a relatively straightforward tool and fairly easy to understand.
The Black and White Tool converts to monochrome by converting colour to greyscale. It gives you control over 6 ranges of colour – red, yellow, green, cyan, blue and magenta. The corresponding greys for each of these 6 colour ranges can be made brighter or darker by adjusting a set of sliders.
Black and White Tool Properties
Presets: These are worth a look to see what effect the different presets have on the slider values.
On Image Adjuster: Click this and a dropper appears. Click anywhere in your image and drag the dropper left (to darken tones) and right (to lighten tones). The adjustment will be made to the original colour below the cursor. This is quite a daft tool and can be safely ignored!
Sliders: In each case, slide left to darken tones and right to brighten tones. You can also enter numbers explicitly into the value boxes to the right of each slider.
Auto: This will automatically convert to black and white.
Tint: Click this to add a single colour. Click the colour swatch to choose any colour. This option is limited when you are working with an adjustment layer. You can also use a black and white adjustment from the Image menu >>> Adjustments >>> Black & White. This gives extra options to adjust the hue and saturation of the tint colour. allowing you to achieve a very precise result. It’s a good idea to use this on a final version of your image as it is a destructive process which will result in information being lost.
Using the Black and White Tool
Add a black and white adjustment layer. The colours in your image will instantly be converted to tones of grey.
Adjust the sliders for each of the six available colours. This determines how bright the corresponding grey tones will be in your converted image. For example, sliding the red slider to the right will brighten all reds in the image. Slide to the left and the reds will be darker.
Optionally, click the tint box to tint your image with a single colour. Sepia tends to be the most popular.
The original image is on the right. Probably not an image which would normally be converted to monochrome but it serves to illustrate how the Black and White Tool works.
Two very different adjustments were made to the red slider. The other 5 sliders are identical in both adjustments.
Below are two versions of the image showing the effects of this single change to the red slider. Drag the slider to the left to see the light version and right to see the dark version.