Greyscale
Greyscale is support by most image type and is most commonly used for electronic documents that need to be printed out on black and white printers (e.g. Fax’s).
If a full colour image is used in documentation when it comes to being printed out (on a standard black and white printer) colours of a similar darkness can blend into each other and the artwork (usually a logo) becomes less defined. However if the same document uses a greyscale image instead this image has already been refined for use with black and white printers and will keep all the detail of the artwork when printed.