BITMAPS
All photographs are bitmaps. That is, the image is made up of tiny dots or picture elements (pixels) of different colours, which combine to form the complete picture. Bitmaps are commonly seen on Windows computers as BMP files, and on Macs take the form of TIFF or EPS.

RESOLUTION
Most monitors have a resolution of between 72 and 96 dpi, but most desktop printers will require 150dpi, and most commercial printers will need 300dpi.

VECTOR IMAGES
On the other hand these are made up of scalable objects, such as lines and curves, defined by mathematical equations. Consequently they are not dependent upon resolution and can be scaled to suit without any loss of quality.

You cannot convert a bitmap image to a vector, but you can convert a vector to a bitmap, but only at the expense of losing its unique attributes.

.eps or ENCAPSULATED POSTSCRIPT
This a container for holding PostScript descriptions of an image. It can be used for both bitmap and vector images, will hold clipping paths and supports millions of colours, as well as RGB and CMYK colour spaces. These files cannot be edited because they are dependent on the program that wrote them. TIFF's on the other hand can be edited through DTP programs, and serious editing with Photoshop.
QuarkXPress also uses a form of EPS known as DCS (Desktop Colour Separations), made up of four files: one for each CMYK colour plus a composite for previews.

.gif or GRAPHICS INTERCHANGE FORMAT
An internet graphics file, the GIF 89a is the most common version. It uses a patented data compression algorithm and has an 8-bit colour palette of 256 colours, resulting in very small file sizes. Although it suports transparency it is best used for illustrations with solid colours.

.jpg. or JPEG or JOINT PHOTOGRAPHIC EXPERTS GROUP
This is used for compressing photographic images. It can result in rather blocky pictures lacking in fine detail. However it makes extremely small files that can be used on websites or e-mailed to colleagues. When compressing there is a sliding scale, so you decide how much quality to trade off against compression. JPEGs are 24-bit with 16 million colours. The moving picture equivalent is an MPEG.

.pdf or PORTABLE DOCUMENT FORMAT
This is a page description format used for exchanging documents in their final format. It may in time replace postscript. It uses a layered file structure, storing vectors, bitmaps, line arts and fonts in different layers, and can therefore apply different types of compression to each producing reasonably small file sizes without compromising quality. You need to be very careful when making PDF's. If you set them up for web or ebook use the result is a very small file without the information needed for high-quality printing. On the other hand, if you keep that information, you will have a file too big for use on the web.

.png or PORTABLE NETWORK GRAPHICS (Alternative to a GIF)
A lossless compression format for bitmap graphics with 256 indexed colours, plus support for 24-bit and 48-bit true colour. It is relatively new and not widely supported at the moment.

.ps or POSTSCRIPT
This is a computer language that describes a page, including the fonts and the graphic elements contained within it, in a form that an output device, such as a printer or an imagesetter, can easily understand. Postscript is a universal format in that virtually every output device can understand it, and is therefore the best format for delivering work to a printer or output bureau.
Postscript files need to be rendered for each device they are printed on, that is, given device-specific information, such as paper size, available colours, resolution and screening. This area is handled by the RIP, or Raster Image Processor and every output device has it's own RIP.

.swf or SHOCKWAVE FLASH
This is a vector format, used by Macromedia for its Flash image and animation program.

.tif or TIFF
Tagged Image File Format. TIFF's have a very wide choice of what information to include, however you may get slight variations between Corel and Adobe. For this reason some designers may choose an EPS over a TIFF. TIFF's can hold both vector and bitmap information, plus alpha channels, paths, and support all colours. It also supports LZW compression.
When you save an Adobe Photoshop image as a TIFF, you can choose to save in a file format for IBM PC-Compatible or Macintosh computers. To compress the file automatically, click the LZW Compession check box. This decreases its file size.
As a rule, at Fox we tend to use EPS for all images containing vectors or paths and TIFF's for anything else.

.xml or EXTENSIBLE MARKUP LANGUAGE
This was developed from HTML. It is an extremely powerful and flexible, yet simple, way of describing data that can be used for writing databases, spreadsheets and websites.