Friday, May 25, 2007

Refocus your images after the fact

Have you ever taken an out-of-focus picture and wished you could correct your mistake? Or has your artistic side desired to blur parts of a picture even though everything is is sharp focus? After all, you can use Photoshop to make all sorts of modifications to your photographs. But even Photoshop can't help you: you're stuck with the depth of field you used when you took your picture.

That may be changing soon. Ren Ng of Stanford University was awarded the 2006 ACM Doctoral Dissertation Award for his work on Digital Light Field Photography. Ren and his colleagues at the Stanford Graphics lab built a digital plenoptic camera, described in the tech report "Light Field Photography with a Hand Held Plenoptic Camera". A plenoptic camera is

...a camera that samples the 4D light field on its sensor in a single photographic exposure. This is achieved by inserting a microlens array between the sensor and main lens, creating a plenoptic camera.

This microlens array is analogous to an insect's compound eye.

Each microlens measures not just the total amount of light deposited at that location, but how much light arrives along each ray. By re-sorting the measured rays of light to where they would have terminated in slightly different, synthetic cameras, we can compute sharp photographs focused at different depths. ... we demonstrate that we can also compute synthetic photographs from a range of different viewpoints.

And that allows one to refocus the image even after one has taken the picture! You can see examples of refocused images if you follow the above link to the tech report. Utterly fascinating stuff! Ren is now at a startup called Refocus Imaging that is commercializing these ideas.


Alon Halevy said...

I take partial credit for this amazing innovation. I worked quite a bit with his adviser at Stanford, Pat Hanrahan, and probably bored him to death on multiple events, therefore enabling him to think about refocusing in a focused manner.

Pandu Nayak said...

This suggests a strategy for coming up with such amazing innovations...:-)

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