Fine tuning for speedy download times

In the relentless pursuit of web page optimisation, images are frequently cited as the main culprits when it comes to slow download times.

Large image file sizes are the online equivalent of concrete boots, but even after optimising images for the web, there may still be some scope for fine-tuning. In some cases saving an image as a GIF instead of a JPEG may trim a fraction more off the download time without losing quality.

Photographic images should be formatted as JPEGs, but graphic images, with relatively few colours, can be saved as GIFs and still look sharp. A company logo, for instance, will usually only contain two or three colours, so this is an ideal candidate to be formatted as a GIF rather than saved in the bulkier JPEG format. Drawings, artwork, clip art, icons, black and white photographs and text images are also suitable for GIF formatting.

Generally speaking, the GIF format is best used for images with 16 or less colours that do not bleed into one another. With 256 colours or more, you’re probably well advised to save in the JPEG format. Multicoloured images that are dithered, that is, colours bleeding or overlapping such as in a photograph, will be smaller in file size and sharper when saved as JPEGs.

Both formats compress the image in different ways in order to pack more information into a smaller file size. It is the difference in these compression methods, and the trade offs they employ, that affect the image quality.

Try copying some images from your site and experimenting with both formats. Before long you’ll have a feel for which format to go for.

To copy an online image to the hard disk, right click on the image and select Save picture as. The image can then be manipulated in a variety of packages including Adobe Photoshop, Paint Shop Pro and MS Paint.