Photoshop: the easiest option to have blue and white instead of black and white effect in an image?

Question

I am looking for the easiest and quickest option to apply blue and white (or green and white) to an image.

Basically, I would like to have a shade of another color instead of gray scale in black and white effect.

Answer 1

Start with a greyscale image.

1. Image > Mode > Duotone
2. Click the Black Square and pick your blue
3. Image > Mode > RGB (if your'e not creating an image for print).

Answer 2

The most versatile way would be via adjustment layers:

1. Add blck & white adjustment layer to turn picture into greyscale
2. Add gradient map adjustment layer and edit its gradient colors to ones you need (blue or green to white)

And of course you can do the same through menu, without layers, but layers add that extra tweaking possibilities. Here is more detailed explanation if you need one: http://www.photoshopessentials.com/photo-effects/gradient-map/

P.S. Step 1 could be ommited if I remember correctly.