This is part 25 of the Photoshop quick tip series where you will learn how to convert an image into black and white. I have actually previously created a tutorial that show you how to turn an image black and white which can be found here. I will be briefly discussing these methods in this quick tip.
The first method involves changing the default RGB mode in a colour image to the greyscale mode. This is not the most common method of converting to a black and white image. If you are using Photoshop CS4 you will receive a message asking if you want to discard the colour information. You click the discard button if you want to follow through with the conversion.
The second method is the most common and can be done through the menu bar or using shortcut keys. The default desaturate keyboard shortcut is Shift + Ctrl + U, or the menu bar option is Image > Adjustment > Desaturate.
The third method is similar to the second as it desaturate the image, the only difference is that it takes more time. You again can use keyboard shortcuts (Ctrl + U), or you can go through the menu bar by selecting Image > Adjustment > Hue/Saturation.