There are two different types of file formats – bitmap (raster) and vector drawing.
Bitmap (Raster) Images
Bitmap is the most basic of the formats with each image made up of individual pixels. This format is most often used with photographs and images that contain subtle shading.
There is however one problem with bitmap images, scaling up the image. This is because by scaling up the individual pixels become more pronounced, leading to a jagged appearance. There is the ability to improve this using a technique called anti-alias which acts to smooth the graphic, however this still will result in a jagged appearance as the image is scaled up once more. This again can be improved through increasing the image resolution, however this causes the problem of making the file larger and therefore slower to load.
Programs that produce such files are Adobe Photoshop, Paint Shop Pro and Corel Photo Paint, with file formats including BMP, GIF , JPEG, JPG, PNG, PICT (Mac), PCX, TIFF and PSD. The most popular out of these formats for web pages are GIF and JPEG, the former because of it ability to compress files and therefore speed up loading time, the JPEG because it allows a full range of colors.
Vector Images
Vector images differ because they are made up of paths. This makes them much smoother and clearer as the image I scaled up and is what true-type fonts use to ensure that they lose no quality with changes in size or resolution. It is for this reason that vector drawings are used for page layout / type / line art and illustration.
Programs that produce these types of files are Adobe Freehand MX, Deneba’s Canvas and Abode Illustrator, the file formats include .ai, .cnv, .cdr and .fh8 .
The EPS format is a file type that allows a graphic application that can’t read the file types above and is a format that is likely to be most requested for illustration and line art because of the ability to scale the work with no loss of detail.
Hopefully this makes the scary world of graphic file formats a bit clearer and if your graphic designer is of any quality then as soon as you mention a format they should know exactly what you’re talking about and will be very impressed if you do too!