rmotion

RMotion

• RMotion provides a simple interface to build motion detection software in ruby.

Author

• Riccardo Cecolin
• rikiji at playkanji dot com
• http://www.rikiji.it

Documentation

• You need libopencv-dev, libhighgui-dev and libfftw3-dev to compile this extension.
• For usage examples check examples/first.rb and examples/second.rb
• http://www.rikiji.it/post/19

Require the lib, instantiate the main object and print default options:

irb(main):001:0> require 'rmotion' => true irb(main):002:0> m=Motion.new => #Motion:0xb74d14a0 irb(main):003:0> m.show? => true irb(main):004:0> m.write? => false irb(main):005:0> m.fft? => true

http://www.youtube.com/watch?v=HNL-2pNkuSo&feature=player_embedded

show, write and fft are the most important options. When show is true the video analyzed is also displayed in a window. You can set write to a string (a filename) to save the video analyzed to a file! Both displayed and saved video will have motion detection markings on it, like the video i just showed to you.

fft manages how the video frames are processed (fast fourier transform or direct): i recommend to set it always true, except in case your cpu isn't fast enough to follow the stream in realtime. Soon i'll post an in-depth analysis of what's the difference between fft=true and fft=false.

irb(main):006:0> m.fill? => true irb(main):007:0> m.rect? => false irb(main):008:0> m.point? => false

Next group of options is about output frames: fill default true behaves like the previous video, rect draws rectangles around moving objects and point draws instead a small circle centered on the object. Let's see them! Note that i can swap them live!

http://www.youtube.com/watch?v=0LQIt0XiWqE&feature=player_embedded

irb(main):012:0> m.threshold_fft? => 1.0 irb(main):013:0> m.threshold_direct? => 8.0 irb(main):014:0> m.threshold_distance? => 9.0 irb(main):015:0> m.threshold_group? => 20

threshold_fft and threshold_direct values influence what is recognized as noise and what as an object. Note that they are used in a mutually exclusive way: if fft is true then threshold_direct won't affect result. Same for fft as false and threshold_fft. Play with those value to fit your enviroment (light, object speed..).

threshold_distance and threshold_group also have a role on recognizing objects: an object is a group of al least group cells distant each other no more than distance. So you can choose min size of objects and spread of cells. Cells are a group of pixel determined dynamically on camera resolution, so don't worry about it.