How to improve quality of pictures that are already taken (if possible in GIMP)?

Question

I'm not a photographer but a graphic designer.

In GIMP, I only discovered two methods of improving the quality of an photo:

Filters > Enhance > Unsharp MaskNoise > HSV Noise

Basically, I would like to remove some blurriness and 'fake' high resolution, if possible (I don't mind adding some noise).

I like this final result: http://www.blog.spoongraphics.co.uk/about (the guy in the picture).

Any other suggestions?

Answer

There are many ways to improve an image, and sharpening and noise reduction are just the very start. These techniques are almost completely program-agnostic, and can be done using a variety of different tools, Gimp included.

In photography, this is a major portion of the work that is done, and has become known as "Post Processing" or simply "Post".

Post-Processing Techniques:

Basics

• Cropping
• sharpening
• white balance correction
• Contrast enhancement
• spot touchups/dust removal

Advanced

• noise reduction
• cross-processing
• halftone/duotone
• HDR

These lists are by no means exhaustive, but merely show a few of the more common techniques.

There are quite a few tutorials around that may be helpful for you.

Check more discussion of this question.