Optimisation task

In today's interactive media seminar I was given a task of optimising an image for use on a website.

The original image is a jpeg with dimensions of 1000 pixels by 1000 pixels at 300 dpi.

The image source is: http://en.wikipedia.org/wiki/File:SurfaceTension.jpg

The image above has a file size of 581 KB.

I re-sized the image using Photoshop to 500 pixels by 500 pixels at 150 dpi. Here is the result:

The image above has a file size of 329  KB.

I then saved the image as a gif at 500 pixels square; here is the result:

The file size of the gif image is 149 KB. The reduction in quality is clearly visible as the gif format does not use as many colours as jpeg; this is most noticeable in the green area in the bottom right corner of the image. I believe this format would be most suitable if there is an image with a small number of colours such as a logo or button; otherwise I would use jpegs for detailed images.