3 things to check for better motion detection
Written by Joe Janson,
Project lead at Omega Unfold Inc


Many things can go wrong during a motion detection process, resulting in misses and false positives. Because conditions change throughout the day, you need to optimize the setup in order to get reliable results. Here are the things to watch out for.



iPhone/iPods on a wifi networkGet the right camera for the job

There is no substitute for good video source, there is no such thing as a software "enhance" feature that takes a crappy image and cleans it up.


The resolution of the camera refers to the amount of pixels in an image. This can be represented as a width/height measure (640x480), a mega-pixel value (640x480 = 0.3 mega pixel), or number of lines in the case of analog cameras. A good image resolution is useful when you want to record images or video, but it has little impact on the quality of motion detection.

The price of the camera is usually the better clue for the camera's quality; remember that a cheap camera can have a high resolution, but this does not mean that it will provide great colors and decent frame rate, nor that it will perform well under low light conditions.

Bigger images put a larger load on the video capture, which may slow down the computer. You may need to experiment and tune the settings to find a balance.

Many webcam do not have adjustable lens, have a simple lens that you need adjust manually to set the focus. A few high end webcams have auto-focus mechanical lens, which provide better images, but at a cost: if something moves out of focus, the camera will try to re-focus, which may trig the motion detection.

iPhone/iPods on a wifi networkLighting is everything

Again, there is no substitute for a good source image. Webcam behavior changes with lighting: When the scene goes darker, the camera compensates by increasing the voltage in the video sensor, making it more sensitive. The downside is that this voltage increase produces noise in the sensor, resulting in grainy images (see picture below for example).

If a camera measures 1% noise from a well light room, the same camera may well measure 3% noise from the same dim light room. Another camera may behave differently. This lack of stability in light reading is a problem because it makes it harder to adjust the motion sensitivity.


Darker scenes produce noisy images.

A darker scene also means that camera may spend more exposition time for each frame, resulting in a lower frame rate acquisition.

On the other side, it is possible to provide too much light, this can sometime happen for cameras looking outdoors. In this case, the image, or part of the image, will saturate to white, making it impossible to see anything.

Higher quality cameras can deal with a wider range of lighting scheme. Cheap cameras will usually mis-behave in dark or too-bright environments.

Here are a few important points that you should consider when setting up motion detection:
  • Good motion detection results require contrast between moving subjects and the background.
  • Less light means less contrast, resulting in misses.
  • Moving shadows and lens flares can also produce important changes in contrast, generating false-positives.
  • In a dark scene, if a moving subject passes between a light source and the camera, this produces major contrast, which results in reliable trigs.

iPhone/iPods on a wifi networkPlace motion detection Hot Spots strategically 

This is where the Webcam Zone Trigger software gives you a huge advantage over standard motion detection software. You get to choose the size and position of the area to monitor by placing a motion detection Hot Spot object on the image.

How to Use motion detection Hot Spots
Place motion detection hot spot strategically for best results
  • Place the Hot Spot over a stable area, where you expect there will not be irrelevant motion, or where there is less noise.
  • The percentage next to the Hot Spot is the measured motion and noise.
  • More motion means a higher percentage.
  • Set the Spot's sensitivity to a slightly higher percentage threshold.
  • Make sure the spot turns blue when the motion you expect occurs.
  • If the Hot Spot is too sensitive, it will turn blue for no reason, slide the sensitivity to the left to make it less sensitive.
  • If the spot does not turn blue upon motion, slide it more to the right until it does.

More tips to get better results with Hot Spots:
  • Use smaller hot spots. They will require less motion to trig, and you can tune them more precisely.
  • Use Hot Spots as trip-wire. In a dark scene, place Hot Spots over a light source (see image above), this way if something moves between the light and the camera, this will produce optimal contrast.
  • You can use many hot spots. You can overlap them. You can set a different sensitivity settings for each one.





References

http://www.zonetrigger.com - Motion Detection software download site
Download a free copy of the Zone Trigger software.


If you have questions about the Zone Trigger products or if you require consultation and advice on your computer vision projects, please contact Omega Unfold's technical support: support@zonetrigger.com






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