From what you describe, the easiest thing would be to put it in a layer set to darken. But search for similar issues, since this subject has been covered any number of times, and depending on your exact needs there could be better solutions.
There are several ways. Here’s one that is foolproof:
Go to Channels. Command-click on the composite channel (RGB or CMYK or Gray. You will get a selection. Command-Shift-I to inverse the selection.
Back to Layers. Create a new layer. D for default B&W. Option-Delete to fill the selection with black. Trash the original layer.
This will also work with colors other than black.
Ed
Is there an advantage of the way you just mentioned over the following?
Layer Style palette > Blend If Gray > This Layer (right delta moved to left slightly)
Ron,
Tnat’s a good method too, but if you have antialiasing, which you probably will, you have to keep an eye on it so the Blend If dosn’t cut away some of it. Or leave some you don’t want. The channel way just gives you your line with no judgement needed.
Also, Blend If makes the white pixels transparent but doesn’t eliminate them. To get rid of them entirely you must merge with a transparent layer.
Ed,
Just to clarify from your original post, what do you mean "D" for default B&W?
If you press the D key the color picker will change to the default, black foreground/white background.
