Aquarium Surveillance

Surveilling fish in an aquarium with a simple webcam is a fun activity for young and old. The following post describes a simple software setup that was used to continuously upload live still images of a small aquarium.

Nothing more is required than an aquarium, a webcam and a Linux computer with Internet connection. Optionally the aquarium may be substituted by a hamster cage. ;)

Probably ffmpeg could be used as an alternative to stream live video. However it was found that ffmpeg crashes rather often and that the encoding of popular video formats is CPU intense, which is especially infeasible on older computers. Another alternative for live video would be to use mjpegstreamer, which is especially resource preserving. Unfortunately the project seems to be inactive now and no 64-bit binaries are provided.

Therefore it was concluded that the best compromise would be to stream still images at the maximum resolution of the webcam and a refresh rate of a couple seconds. Many programs are suitable to acquire images. In this case fswebcam was chosen, because it is small and simple and can be found in the Debian/Ubuntu repositories.

Watching the fish should also have a social component. Therefore an Xajax sample program was used to provide a simple comment function ("graffiti wall"). The sample program can be tested and downloaded here.

The following packages need to be conveniently installed from the software repositories if not already present:

sudo apt-get install apache2 php5 fswebcam

Normally the images acquired with fswebcam would be written to disk continuously. To avoid letting the hard disk suffer too much, a ramdisk is created. This can easily be done by adding the following line to /etc/fstab:
#ramdisk for aquarium photos
ramfs  /var/www/aquarium/aqua_ramdisk ramfs defaults 0 0

You can download the script and the modified xajax web program here.

The webcam.sh script needs to registered for automatic startup. A description how to do this can be found here. The web program can simply be copied to the apache web folder eg. /var/www/aquarium.

Creating Timelapse Videos with a Webcam

Last week I had some fun creating timelapse videos using just an inexpensive webcam and a laptop. Timelapse videos are a nice way to visualize processes which are otherwise to slow to observe directly (eg. the movement of clouds or the growth of plants). Technically the the solution to all the world's problems seem to be little Python scripts, which can be downloaded here. ;)
For simplicity a lot of things are hardcoded in these scripts, so you most certainly have to make changes. The scripts should be easy to understand, as they are quite short and simple. However if anything is unclear, just drop me a comment.

timelapse.py, timelapse_copy.py

timelapse.py uses ffmpeg for capturing images from the webcam (support for v4l assumed). You do not need this script, if you have any other means of acquiring the individual frames. The filenames of the acquired images contain a consecutive nr. and the time and date when the image was taken. Unfortunately it turned out later that times and dates in the filename confuse ffmpeg and have to stripped away to join the individual frames to a single video file. Besides the nr. needs to have leading zeros. The timelapse_copy.py script was made to compensate for that.

timelapse_filter.py

As mentioned before, an inexpensive webcam was used for simplicity. Therefore a Gimp plugin is used to sharpen and denoise the pictures a little. The script uses Gimp and the package gimp-plugin-registry (for the wavelet denoise). You can skip this step if you have a good camera or are not willing to wait, because the filtering can take quite some time, depending on which filtering operations you want to run on the individual frames. Do not forget to copy this script to ~/.gimp-2.6/plug-ins and to make it executable.

timelapse_ffmpeg.py

A third script creates a video from the filtered images again using ffmpeg.