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Photography and the web
Web graphic formats
JPEG (Joint Photographic Expert Group)
The most popular format for photos on the web is JPEG. This is a 'lossy' format (each time you open and save a JPEG you lose information) so you should only ever save an image as a JPEG once you've finished working on it.
Most graphics editors let you adjust how much compression you want to apply to an image, so it's best to experiment to find an acceptable compromise between image quality and file size.
Be careful how you compress the image: too little and it'll weigh a ton, too much and it'll look horrible. Tip: blurring a JPEG image slightly can result in substantial file size savings.
GIF 97a/89a (Graphical image format)
GIFs files can only support a maximum of 256 colours and use LZW compression to substantially reduce file sizes.
While this is great for flat colour artwork and type, it can wreak havoc with photographs containing millions of colours, adding weird 'dotty' effects and colour banding (as GIFS can only contain a limited amount of colours something like a graduated sky will be reduced to unnatural bands of colour).
However, photographs that only contain a few hues can be compressed very successfully with the added bonus of transparency support - so you can make your images appear to 'float' on the page background.
PNG (Portable Network Graphics)
Hastily springing into life in 1995 when it looked like CompuServe were going to demand royalties from everyone using GIFs, PNGs offer better compression rates than GIFs with no loss of information like JPEGs.
With these clear benefits, the PNG format should have set the world alight, but due to Netscape and Microsoft's reluctance to adopt the format quickly, limited browser support means that you're better off ignoring it for now.
Article © Mike Slocombe 2001
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