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filesize optimisation

The basic factors to reduce filesize for each of the two web-compatible graphics formats, gifs and jpegs, have been discussed earlier. As a summary:

Make all images the correct resolution for most monitors - 72dpi. Anything higher is pointless.

Try the image as both a gif and jpeg, copying each as you push the factors to reduce filesize. As you can see, the effectiveness of the filesize reduction depends on the type of picture you're working with. Remember that the comparison between jpeg and gif varies according to the size of the picture. Generally speaking, a jpeg's advantages are greater than a gif's as the size of the picture increases, unless the picture contains large areas of single colours.

On small graphics such as these, you can see that the amount of filesize saved is barely worth the quality lost - but try it with bigger pictures and you may find it is worth reducing the number of colours or adding compression. Just remember to save an uncompressed full-colour original!

Full-colour illustration:

Jpeg 7K minimum compression	Jpeg 4K 30% compression	Jpeg 3K 50% compression	Jpeg 2K 70% compression
Gif 10K 256 colours	Gif 9K 128 colours	Gif 6K 32 colours	Gif 4K 16 colours

Photo:

Jpeg 10K minimum compression	Jpeg 3K 30% compression	Jpeg 3K 50% compression	Jpeg 3K 70% compression
Gif 9K 256 colours	Gif 9K 128 colours	Gif 6K 32 colours	Gif 4K 16 colours

Line Drawing :

Jpeg 12K minimum compression	Jpeg 6K 30% compression	Jpeg 5K 50% compression	Jpeg 4K 70% compression
Gif 6K 256 colours	Gif 5K 16 colours	Gif 4K 8 colours	Gif 2K 2 colours