Open an image that has a subject with striking colour. We’ll keep this colour and turn everything else black and white. The Magic Wand tool is ideal to select colour. Choose the tool, and then untick the Contiguous box in the Options bar. This makes sure the tool selects colour across your entire image. Make sure the Anti-alias box is ticked and the Tolerance is set to around 75px.
Click anywhere on the colour that you want to keep. You can increase the Tolerance number if the tool has failed to cover much ground. Ctrl/Cmd+D to remove the selection if you need to start again. Continue to select more of the same colour by holding Shift while clicking. Hold Opt/Alt while clicking to remove areas of the selection that happen to overflow.
For the effect to work well, be sure to select as much of the colour as possible. Try to get close to the edges where the colour meets other colours. You can lower the Tolerance to get a more accurate selection as you go. Flick between the normal version of your image and the Quick Mask mode (Q) to see just how your selection is taking shape.
In Quick Mask mode the areas of red will not be included in the selection and areas that show will be. If you can spot any small specks of the image coming through the Quick Mask that shouldn’t be there, use the Brush tool set to black to retouch them and apply a mask. Use the Eraser tool to remove parts of the selection that shouldn’t be masked.
When you’re confident that the mask is accurate and the selection looks good around the colour you want to keep, press Cmd/Ctrl+Shift+I, or go to Select>Inverse. This flips the selection. Go to Layer>New Adjustment Layer>Black & White, and what you should see in the Layers palette is a new adjustment layer with a mask moulded to the selection that was just made.
The Black & White adjustment layer gives your image a basic conversion from colour to monochrome. But this adjustment layer contains a number of sliders and also presets, which can mix up the monochrome effect. Firstly, cycle through the presets to choose one that brings out the most detail in the black and white areas. The option Lighter works well if your image has lots of sky involved.
There is a collection of sliders in this adjustment that change the look of the black and white effect. Each slider represents a colour, and by increasing certain ones you’ll be able to retrieve details from the parts of the image that are in shadow. There are no rules to this, as it’s really down to which one you think looks the best.
[this post syndicated from Photoshop Daily]