Use an intervalometer to detect footprints
Automated disclaimer: This post was written more than 15 years ago and I may not have looked at it since.
Older posts may not align with who I am today and how I would think or write, and may have been written in reaction to a cultural context that no longer applies. Some of my high school or college posts are just embarrassing. However, I have left them public because I believe in keeping old web pages alive—and it's interesting to see how I've changed.
While Alex was in town for the weekend, we used my camera's intervalometer to record tracks in my gravel driveway. I'm still playing with the images, but I've got a pretty sweet sample uploaded to BoF Labs.
I set up the camera on a tripod and told it to take 1 image per minute for 7 minutes. The first image is useless because the tripod slowly settles over the course of the first minute. Between each pair of photos we made tracks in the camera's field of view.
- Pristine driveway
- This is the baseline image.
- Driveway with tracks
- I doubt you can see the footprints we made in the "after" photo, partly because the baseline image was already covered in tire, foot, and paw tracks.
- Difference between images
- I used the GIMP to subtract the former picture form the latter, which reveals the footprints as light areas in a sea of dark.
There was some tripod shift between other photo pairs, and I'm still working on aligning the photos. Already I'm thinking of other surfaces that might support before/after subtraction for tracking purposes. Carpet? Grass? Sand?
Mindy says:
Those are pretty sweet. Even without the third picture, you can definitely see a difference between the pictures flipping back and forth between them. It's hard, as you say, to detect the exact tracks (because you can't see them with the naked eye just by looking at the second picture alone). Even so, it's neat to flip between the two and then look at the third picture. I think the sand would be a lot fun to try, as well as picking up tracks better.