I wrote recently about the hardware involved in my Raspberry Pi motion-detecting wildlife camera. Here are some more details.
The motion detection software
I started with the simple and clever motion-detection algorithm posted by "brainflakes" in a Raspberry Pi forum. It reads a camera image into a PIL (Python Imaging Library) Image object, then compares bytes inside that Image's buffer to see how many pixels have changed, and by how much. It allows for monitoring only a test region instead of the whole image, and can even create a debug image showing which pixels have changed. A perfect starting point.
As part of the PiDoorbell project, I had already written a camera wrapper that could control either a USB webcam or the pi camera module, if it was installed. Initially that plugged right in.
But I was unhappy with the Pi camera's images -- it can't focus closer than five feet (though a commenter to my previous article pointed out that it's possible to break the seal on the lens and refocus it manually. Without refocusing, the wide-angle lens means that a bird five feet away is pretty small, and even when you get something in focus the images aren't very sharp. And a web search for USB webcams with good optical quality was unhelpful -- the few people who care about webcam image quality seem to care mostly about getting the widest-angle lens possible, the exact opposite of what I wanted for wildlife.
Was there any way I could hook up a real camera, and drive it from the Pi over USB as though it were a webcam? The answer turned out to be gphoto2.
But only a small subset of cameras are controllable over USB with gphoto2. (I think that's because the cameras don't allow control, not because gphoto doesn't support them.) That set didn't include any of the point-and-shoot cameras we had in the house; and while my Rebel DSLR might be USB controllable, I'm not comfortable about leaving it out in the backyard day and night.
With gphoto2's camera compatibility list in one tab and ebay in another, I looked for a camera that was available, cheap (since I didn't know if this was going to work at all), and controllable. I ordered a used Canon A520.
As I waited for it to arrive, I fiddled with my USB-or-pi-camera to make a start at adding gphoto2 support. I ended up refactoring the code quite a bit to make it easy to add new types of cameras besides the three it supports now -- pi, USB webcam, and gphoto2. I called the module pycamera.
When the camera arrived, I spent quite a while fiddling with gphoto2 learning how to capture images. That turns out to be a bit tricky -- there's no documentation on the various options, apparently because the options may be different for every camera, so you have to run
$ gphoto2 --set-config capture=1 --list-configto get a list of options the camera supports, and then, for each of those options, run
$ gphoto2 --get-config name [option]to see what values that option can take.
Once I got everything working, the speed and shutter noise of capturing made me wonder if I should worry about the lifespan of the Canon if I used it to capture snapshots every 15 seconds or so, day and night.
Since I still had the Pi cam hooked up, I fiddled the code so that I could use the pi cam to take the test images used to detect motion, and save the real camera for the high-resolution photos when something actually changes. Saves wear on the more expensive camera, and it's certainly a lot quieter that way.
To get the images off the Pi to where other computers can see them, I use sshfs to mount a filesystem from another machine on our local net.
Unfortunately, sshfs on the pi doesn't work quite right. Apparently it uses out-of-date libraries (and gives a warning to that effect). You have to be root to use it at all, unlike newer versions of sshfs, and then, regardless of the permissions of the remote filesystem or where you mount it locally, you can only access the mounted filesystem as root.
Fortunately I normally run the motion detector as root anyway, because
the picamera Python module requires it, and I've just gotten in the
habit of using it even when I'm not using python-picamera.
But if you wanted to run as non-root, you'd probably have to use
NFS or some other remote filesystem protocol. Or find a newer version
Testing the gphoto setup
For reference, here's an image using the previous version of the setup, with the Raspberry Pi camera module. Click on the image to see a crop of the full-resolution image in daylight -- basically the best the camera can do. Definitely not what I was hoping for.
So I eagerly set up the tripod and hooked up the setup with the Canon. I had a few glitches in trying to test it. First, no birds; then later I discovered Dave had stolen my extension cord, but I didn't discover that until after the camera's batteries needed recharging.
A new extension cord and an external power supply for the camera,
and I was back in business the next day.
And the results were worth it. As you can see here, using a real camera does make a huge difference. I used a zoom setting of 6 (it goes to 12). Again, click on the image to see a crop of the full-resolution photo.
In the end, I probably will order one of the No-IR Raspberry pi cameras,
just to have an easy way of seeing what sorts of critters visit us at
night. But for daylight shots, an external camera is clearly the way
[ 20:09 May 24, 2014 More hardware | permalink to this entry | comments ]