Camera

Prototype code for live QR code recognition.

Eventually we'll use the position of the QR code as error data for a control system that tries to centre the camera on the QR code.

Install

On OS X, you should use Homebrew. Do the following:

$ brew tap homebrew/science
$ brew install opencv
$ brew install zbar

On Ubuntu, something similar such as $ sudo apt-get install opencv zbar will probably work.

Run $ python -c "import cv2" && echo "It works!" to make sure it worked.

Install Python libraries:

$ pip install pillow
$ pip install git+https://github.com/npinchot/zbar

Camera

Here are the things we'd like the camera to do:

Raw Capture

capture raw video, discard all but latest frame.

• What would be a zbar-friendly format? Have a look at https://github.com/ZBar/ZBar/blob/854a5d97059e395807091ac4d80c53f7968abb8f/zbar/convert.c and https://github.com/mattvenn/qr-music-player/blob/master/picam_qr.py.

  => Gabi worked out ZBar will only scan grayscale images ("Y800"). We can get grayscale using the Y channel of the Pi's raw YUV image.

• shared memory? This would be nice for zero-copying things between processes, so different things can do stuff with the camera stream. This looks useful: http://stackoverflow.com/questions/5549190/is-shared-readonly-data-copied-to-different-processes-for-python-multiprocessing/5550156#5550156

Have to use use_video_port=True so the field of view doesn't change while grabbing frames.

Still capture

periodically capture still images to jpeg

For aerial photography.

• consistency might be important? http://picamera.readthedocs.org/en/release-1.8/recipes1.html#capturing-consistent-images

Live stream

capture h.264 video, resized to be smaller (eg. using resize=(1024, 768))

For streaming live video over wifi.

• How can we stream this using UDP?

  python gstreamer-rtsp?

  raspivid -t 0 -h 480 -w 640 -fps 25 -hf -b 1000000 -o - | gst-launch-1.0 -v fdsrc ! h264parse ! rtph264pay config-interval=1 pt=96 ! udpsink host=127.0.0.1 port=1234

  http://www.jonobacon.org/2006/08/28/getting-started-with-gstreamer-with-python/

  http://stackoverflow.com/questions/7669240/webcam-streaming-using-gstreamer-over-udp