It's possible to link to a file of any sort of graphics format. But if we want the image to appear on the page then we want to pick a format which (a) is supported by the browser and which (b) downloads quickly.
Browser support is getting broader, but not broad enough. Any browser should support GIFs and JPEGs. AOL also supports their own ART format and MSIE can be extended to support that as well. Several browsers support BMPs. Most modern browsers support PNGs but not all of their advanced features (such as alpha tansparency).
In the following list, if an image loads alongside the description then your browser supports that format:
| GIF | |
| Transparent GIF | |
| JPEG | |
| PNG | |
| Transparent PNG | |
| BMP | |
GIFs are a lossless compressed format, useful for logos, text, icons and other simple images. They can be transparent and animated. They are limited to 256 colours. To make them smaller, reduce the number of colours used.
PNGs are rather like improved GIFs, they have no limit on the number of colours and support clever transparancy options. Support is rather lacking at the moment. Use them for full-colour maps and diagrams where clarity and colour are needed and where is people need the information they will get the software required. Within a few years PNGs will be 'safe' to use on ordinary web pages.
JPEGs are a lossy compressed format. The example above is over-compressed to show the existance of JPEG artifacts (the messy bits surrounding the text). JPEGs are good for cramming images with lots of colours into a small package. Use them for photographs. To make them smaller increase the level of compression until the quality becomes unacceptable for your purpose.
I can't think of a good reason to use a BMP in a web page. The BMP above is 15kb, all the other images are about 1kb.
How you generate your graphics depends on what software you use. There are a vast number of possible choices. It all comes down to what you have, what you know how to use and what you are prepared to pay for.