This morning while eating my porridge, I read todays article on 24ways by Paul Robert Lloyd in which he links to an article outlining a technique for better image compression. I decided to try it out myself and post the results.
The image I decided to test is an old photo of mine which has a good mix of detail and colour gradients. Below is the starting image with dimensions of 1000px by 667px with 80% compression (file size: 168KB):
Now the same image with dimensions increased to 2000px by 1334px with 15% compression (file size: 70KB):
And finally, same larger dimensions but with 5% compression (file size: 57KB):
In this example, there is noticable degredation in the sky but the main focal point stands up pretty damn well considering nearly a 300% drop in file size.
Definitely a technique to be considered carefully as it may not be suitable for all situations but certainly worth testing on projects to see where precious kilobytes can be saved.