Most digital cameras give the photographer the option of changing the 'picture style' to a monochrome setting.
Most digital cameras give the photographer the option of changing the 'picture style' to a monochrome setting. This 'monochrome' setting on your digital camera basically just combines the different colour channels (red/green/blue) saving only the total brightness – not the colours themselves. For example, something that was 50% red, would look the same as if it were 50% green, or 50% blue – all would become indistinguishable as 50% black (AKA grey). Of course, the fact that they were different colours originally is of huge value in post processing the black and white image, allowing you to separate them, perhaps choosing to make red things become darker grey than green things and so on. Unless you are also shooting in RAW (see below), setting your camera to shoot in monochrome (AKA black and white) setting is a bad idea. While this option can produce reasonable results occasionally, the colour data (which is now lost) actually held a lot of valuable information which would have been very helpful in post production, allowing you to separate out or process differently the parts of the image that were different colours but similar brightness. Converting to black and white yourself later gives you significantly better control of your end result.