Introduction to Raspberry Pi

Raspberry Pi Camera

The Raspberry Pi has the unique ability among hobbyist embedded systems to interface with a camera. As the Raspberry Pi is based around essentially a smartphone CPU, it uses a camera very similar to a cellphone camera. Some other embedded platforms (Arduinos, PICs, etc...) are too slow to make use of live video feeds. Other platforms (Beaglebone for example) are fast enough to process video, but it places a large burden on the CPU. The Raspberry Pi's graphics processor is responsible for handling all camera data so the CPU doesn't have to. This means the camera can record high quality FullHD (1080p30) video without stressing the Raspberry Pis CPU, leaving it available for other tasks (motor control, machine vision, serving Internet requests). For still pictures the camera has a resolution of 2592x1944 (5 Megapixels). There are two variants of the Raspberry Pi camera, a normal camera and one with the infrared filter removed. The latter is called the Pi NoIR and is meant for scientific research, education or infrared photographers. Images taken with PiNoIR are not meant for everyday use (don't take friends and family snapshots with them).

Connecting the camera

The camera is connected through a flex cable, see pictures below for more detail.

Enabling the camera

Before use, the Raspberry Pi must be setup to use the camera. From a command line terminal run:

pi@raspberrypi: sudo raspi-config

Select option 5, "Enable Camera". You will be asked if you want to enable or disable the camera, choose "Enable". Select "Finish" at the bottom of the menu page. You will need to reboot before the camera is available for use.

Taking Pictures/Videos

The camera can be controlled either through a command line interface. There are three utilities available, raspistill, raspivid, and raspiyuv:
* raspistill - Basic camera application * raspivid - Records live video * raspiyuv - Camera application but outputs uncompressed (large) images. These are similar to RAW images if you are familiar with digital photography

While each of these commands have many options, we will only cover the most basic and useful options here. The full set of options can be listed by running the command with a -h argument.

Picture Taking

The most basic use of the Raspberry Pi camera is with the command:
raspistill -o output_filename.jpg
This will save a full resolution image to outputfilename.jpg. If you'd like to copy this file off your Raspberry Pi, the easiest way is to use scp. If your host computer is Windows, I recommend the WinSCP program. IF your host computer is OS X or Linux, run:
`scp pi@<raspberrypiIP>:~/outputfilename.jpg ./`
You can also upload the image to an image viewing website like flickr or Facebook.

A few of the more important options to raspistill are:

There are also many other options as you would expect from a camera: exposure modes, metering modes, even Instagram-like filters.

Recording a video

To record a video, use raspivid. By default, the camera will record five seconds of HD video and then stop. To change the duration, use the -t ms option. Setting a time of 0 milliseconds will record indefinitely (until disk space runs out). _ It is highly recommended to power your Raspberry Pi with a wall wart (not through a computer's USB port) when recording video!_

Basic Example

raspivid -t 0 -o output_video.h264 This will record until stopped (with Ctrl-C for example).

raspivid also has some very useful triggers for creating multiple video files. The camera can stop recording and move to a new file based on time intervals or key presses.

This can be played back using VLC or even streamed live to other computers.

Using camera in Python

To use the camera directly from Python, use the picamera library. The library interface to use the camera is simple to use and offers many of the same controls as the command line utilities.

Before using the library, it must first be installed on your Raspberry Pi. pip (Pip Installs Python) is the application which manages Python packages, and it too must first be installed before use.

<% highlight bash %> pi@raspberrypi:~$ sudo apt-get install python-pip pi@raspberrypi:~$ sudo pip install picamera <% endhighlight %> _source code here

Both flickr and Facebook offer Public APIs to upload your photos directly from python. Using web APIs will be discussed in more detail next week.

Example Source

• Photobooth
• Color picker
• Timelapse
  

FAQ

• Q: Why should I use timelapse mode instead of calling raspistill repeatedly?
  A: Timelapse mode allows you to take more than 1 image per second and to more precisely time the interval between images. Also, the camera needs a small amount of time to warm-up, otherwise color shifts can occur. Using timelapse mode keeps the camera powered on throughout to avoid these color shifts.
• Q: What is the power usage of the camera?
  A: The camera draws about 250mA additional to the Raspberry Pi
• Q: Why does my Raspberry Pi freeze when recording a video? A: Power? Bitrate?

References

• raspistill, raspivid, raspiyuv Documentation
• Raspberry Pi Camera Documentation
• Motion - Detects motion in a webcam