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Overview |
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GCE |
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Marble Challenge |
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ASCIIroids |
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PSD (Second Life) |
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Gravity Bubbles |
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FractalNet |
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EcoSim |
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Cosmic Dust |
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LandMesh |
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Imagencrypter |
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Foxy Detector |
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MacDiff |
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Asteroid Belt |
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Matrix Attack |
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Solar Swarm |
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OS X Terminal |
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Tools |
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Names :-) |
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Foxy Detector
 Foxy Detector (FD) is a motion detection program which I wrote from scratch in about 850 lines of Java. It monitors the image from a webcam which is watching our garden, and plays an alert sound whenever it detects a moving object which might be our “Foxy”. By leaving this program running all day, we can be alerted whenever Foxy visits our garden, without having to keep looking out of the window! Motion detection
FD loads a new image from the webcam every 5 seconds, and then compares the current image (shown in the New tab) with the previous one (shown in the Old tab). The difference between the two images is shown in the Diff tab – white indicates difference, black indicates no difference:  Several sensor areas are defined, in which FD will look for moving objects. Each sensor area is divided into a grid of small square cells, and FD checks the amount of difference in each cell every 5 seconds. If a cell’s difference is greater than a pre-defined threshold, it’s marked as active, and is drawn in red. In the images below, Foxy walks into view between the previous and current images (1 and 2). The difference is calculated (3), and the active cells are drawn in red (4).
If the total number of active cells is between two user-defined limits, min cells and max cells, then an alert sound is played, and the event is recorded in the Log tab. Here, Foxy has activated 32 cells, and since this number lies within the limits of 10 and 80 cells (min and max), the alert sound is played. Settings
The min cells and max cells limits can be adjusted in the Settings tab:  The min cells limit ensures that very small moving objects are ignored. For example, in the images below, a jay is moving, activating 6 cells. The jay does not trigger the alert sound, because the min cells limit has been set to 10.
The max cells limit ensures that changes in sunlight brightness are ignored. For example, in the images below, the sun suddenly goes behind a cloud, and the drop in brightness activates 495 cells. This does not trigger the alert sound, because the max cells limit has been set to 80.
The diff sensitivity control determines how sensitive FD is to differences between the previous and current images:
The contrast and brightness controls can be used to enhance the webcam images during the twilight periods of the day:
Sensor areas XML file
The sensor areas are defined in a simple XML file, which allows them to be easily modified:
Night vision
We own a camcorder which features a night vision mode with an infrared illumination lamp. This allows us to obtain night-time pictures of our garden: 
FD can use these night vision images to detect Foxy visiting our garden at night.
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Contact me – Page last updated on 7th August 2008 – Website hosted by 5quidhost (highly recommended!) |  |
