Aside from infrared (which is super neat but you have to convert your entire camera for its purpose), there are 5 ways I know of to convert an image from color to black and white. I never...ever take black and whites in camera unless I'm using film or digital infrared.
1.
The easiest way to do it (Photoshop) is go to Image>Mode>Grayscale
I would only use this to get a basic representation of how the image would look and if I even want it black and white.
2.
Another method is Image>adjust>Desaturate
But I never actually use this either.
3. 1 channel
You could see how any one particular color channel would look on its own. I would actually use this with some images.
Open the Channels palette>look at the individual channels (red and green are good for most applications IMO). Click on a channel that looks best and go to Image>Mode>Grayscale. The brightness values of that channel are retained and the data in the other channels are abandoned. It can make for some cool results.
4. Use lab mode.
Image>Mode>Lab Color
Open the channels pallette, drag Channels B and A to the trashcan. The Lab channel will disappear which leaves you with lightness. Go to Image>Mode>Grayscale
Go to the Laters Pallette and make a copy of the layer your image is on. Change the layer mode to "Multiply" and add more depth and contrast. You can raises or lower the opacity of this layer to change contrast.
5. Channel Mixer (I like this one)
Open the channels palette, look for the channel that shows the best contrast and which shows the best detail. Adjustment Layer>Channel Mixer (mix channels by percentage)
Choose the best channel in the channel mixer dialog box, Check Monochrome for grayscale, and adjust the sliders of the best two channels. In most cases you want to make sure the percentages add up to 100% but there are of course creative exceptions.
If anyone else knows any other methods chime in because that is my black and white bag of tricks.
