How can slightly blurred photos be improved in post processing?

Question

I have heard quotes which say "If its not good, delete it."

I go by that advice, but sometimes you capture some precious moment but you see that photo is slightly blurred because of camera shake. I don't have an IS lens, and it's too late to somehow do it over.

What best one can do in post processing to improve the quality of the picture?

Ideally, I'd like to use Gimp or Picassa for this.

Edit: I came across a video regarding this -
http://www.youtube.com/watch?v=xxjiQoTp864&feature=player_embedded

Answer 1

I used to think that blurring was one of those things that was impossible to recover from in post. Amazingly enough it's possible to take an image that is blurred beyond recognition:

and recover all the original detail if you know the exact blurring function:

So why isn't this done all the time? Well firstly you never know the exact blurring function so you can't create a perfect inverse filter, secondly if you have noise in the blurred image:

this will totally bias the outcome, as the inverse filter is unable to replicate it:

pseudo inverse filters such as the Wiener filter can cope much better with noise but you still get ringing artifacts like the following:

image (c) MathWorks, see http://uk.mathworks.com/help/images/examples/deblurring-images-using-a-wiener-filter.html for more detail

This is a bit of a digression, but it shows that deblurring is at least possible in principle. There are some very clever algorithms that outperform the Wiener filter by guessing what parts of the original image looked like, in order to estimate and reverse the blurrig function, based on the statistical likelihoods of various light patterns existing.

There are some Photoshop plugins that offer image deblurring using such advanced methods, you might want to take a look at the following (which offer free trial versions)

• http://www.focusmagic.com/
• http://www.humansoftware.com/pages1200/ApertureEdit/HSapertureedit111.html

The results are never perfect but for shots that are irreplacable it's better than nothing!

Answer 2

If the photo is blurred due to camera shake, you really don't have many options. While lots of things can be fixed after the fact in post-processing (such as white balance or exposure), camera shake can't be undone. About the only option here is to apply a blur effect to more of the photo that might make it look like it was intentional.

Even without an IS lens, most newer DSLRs (and some of the high end point and shoot cameras) have great performance at higher ISO levels. If you find yourself in a situation where you can't get as fast of a shutter speed as you need, bump up the ISO. Sure, you might get a bit more noise in the photo, but noise can be addressed via software if you wish.

Answer 3

You can try this software: http://smartdeblur.net/ It's able to detect blur kernels automatically.