Motion detect filter for Satcam - motiondetect.mdc

Last Updated - 26 November 2003 19:35:15 gmt

This document contains information on the motion detect filter (motiondetect.mdc) for Satcam. If you don't find an answer to your question, consider searching or asking on our live Bulletin Board - WebcamSat & Satcam



motiondetect.mdc is a filter for Satcam that detects changes in the video stream. It is designed to only pass along frames that exhibit changes beyond defined thresholds.

Here is the link to download motiondetect.mdc. It should be copied into the satcam/modules subdirectory.

click here to download motiondetect.mdc


The motion detect filter takes 2 parameters - "threshold" and "percentchange".

threshold is defined as the numeric difference between the reference frame pixel and current frame pixel which will trigger a "hit". if you have a noisy camera, the threshold figure should be set fairly high (probably in the range of 8-15). Many video digitizers only have 5 or 6 bits of resolution, even though they produce 8 bit data for each color (red, green and blue). As a result, the values can vary quite a bit, even though the video source is stable. It's worthwhile to watch the output of the motion detect filter in the DebugView monitor window to get an idea of how changes in threshold affect the number of reported "hits".

percentchange is defined as the percentage of screen area (percentage of the total number of pixels) needs to change to trigger an image upload. The filter only passes along images that exceed the percentchange value. Again, some experimentation may be required to establish a good value for percentchange in your environment, but something in the range of 5-10% is probably a good starting number.

The following is an example script that uses the motion detect filter. It's a video capture chain that captures with the VCAP filter, then scales with the VIDEOSCALE filter, then tests for changes with the MOTIONDETECT filter, then JPEG compresses the image and finally sends it to the server with TCPPUSH.



Contact support@surveyor.com with any issues on using the motion detect filter.