Made out of people

Photos out of windows

Blogging from Cordoba, old seat of the Roman & later Visigothic Spanish empires, old Moorish capital, home to Maimonides. From an internet machine in the back of "Bar Hollywood" which is running IE 5.0, and thus cannot run Gmail. Since all popups are blocked, I can´t use a lot of websites...

So I´ve been thinking for a bit about the fact that I like to take pictures of scenery out of bus windows. The pictures inevitably turn out to be crap, of course:

- Busses are moving fast, so some scenery is blurry
- Busses are bouncy, so some stuff is shaky
- The windows are dirty, so some stuff has smears in front of it.

Now, the fact that it´s scenery gives us a few nice advantages.

The first of these is a problem of shutter speed; I don´t know how to solve it. But it doesn´t bother me much, if it´s close enough to parallax, it isn´t scenery. Scenery is stuff that stays still when you don´t. The second is interestingly solved by my camera already.
The third should be solvable if the human can contribute a little more information. Specifically, I´m happy to do several things to help improve the shot.

I could move the camera a little, and thus move the dirt marks. I could zoom the shot a little, and thus change the relative location of the (close up) dirt from the (far off) scenery. Last, I could take a bunch of shots and reconstruct an image.

Not many shots, of course: the scenery is doing a lot of moving. But at least a few shots. What if my camera was willing to go into "moving" mode, and I took eight shots on the spot while wobbling my camera around a little? (My camera has this already, just for a different purpose). We could then use reconstruction techniques to build a map of where the dirt was. Call the rest "signal".

Now, of the dirt, some images have it, some don´t. I´m not completely sure how to separate... do we assume that dirt is dark? It occurs to me that there´s a better way: we already know that dirt doesn´t look like the rest of the stuff around it.

So look for places where the area isn´t "smooth", at least compared to the other images around it. Sure, sometimes the "not smooth" will be a castle or something in the background -- but that will be the same for all the images with the castle.

Now, this is a pretty simple idea, and an extension of a technique that´s been around since the 70s. Anyone know of an implementation? I have some images to test it on... or I will when I return. Assuming my iPod doesn´t get stolen or lost or eaten by a grue or suffer a hard disk crash.

For the true fanatics: have a copy of the hand gestures to Swing Low, Sweet Chariot. because ... well, it came across a mailing list.