Image optimisation
Image optimisation is a process of trading off quality against file size. Depending on the graphics file format, each of these two attributes is decreased in different ways: with GIFs, by decreasing the number of rendered colours with JPEGs, by increasing the proportion of interpolated (or "guessed") pixels. Professional web imaging toolsets allow the artworker to play around with these parameters and make a judgement call about the minimum file size consistent with acceptable quality. Every image on the Jetex.org website has been put through this process – except, of course, the image on the left below!
1: Unoptimised - 45.9 KB (need not mean better quality!)		2: Optimised - 22.7 KB