Converting from colour to sepia or black and white using photoshop

(aka Black and White - more than just desaturation)

So you have a colour photo that you want to convert to black and white, monotone or duotone.
There are so many ways to do it, those listed below are just a few, listed in reverse order of my personal preference.

Image>Adjustments>Desaturate

Now you may want to desaturate an image but this is a quick and easy, very rough method.

Image>Adjustment>Desaturate

This just removes all colour from an image without filtering by channels (R, G and B) and often looks a little flat. You can't tweak the way certain colours represent in the black and white result as with other methods. It usually gets an OK result but wait until you see the other methods. If you are creating a Duotone image (two tones, not just black and white but black and another colour) then you will be using the desaturate adjustment in order to switch to Duotone mode - more on that later. If at all possible try using the other methods, especially the Image>Adjustments Black and White feature that started in the CS range (CS, CS2, CS3). This is my least favourite method of converting Colour to B&W.

Black and White (B&W) via Channels

One of the quickest ways is to select the Channels pallette and click to the right of the name of the colour (red, blue or green)