From owner-freebsd-multimedia  Sun Dec  9  2: 2: 7 2001
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From: Søren Schmidt <sos@freebsd.dk>
Message-Id: <200112091001.fB9A1wF25036@freebsd.dk>
Subject: Re: Motion detection software?
In-Reply-To: <Liam.1007847504.837241.1119.1345644620@SKODA>
To: Danny Dulai <danny@ishiboo.com>
Date: Sun, 9 Dec 2001 11:01:57 +0100 (CET)
Cc: multimedia@FreeBSD.ORG
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It seems Danny Dulai wrote:
> >Well, I've done several intrusion systems that use very simple
> >methods to detect motion/changes in pictures, it essentially
> >just does this:
> >
> >        for (i=0; i<sizeof(pic); i++)
> >             sum += square(pic1[i] - pic2[i]);
> >        if (sum > TRIGGER)
> >            return MOTION;
> >        else
> >            return 0;
> >
> >The two pictures are raw 320x240 8bit/pixel B/W in this case.
> >The TRIGGER value can in this case be around 200000, it has to be
> >low enough to see the changes, and big enough that bitnoise
> >doesn't trigger it wrongly. Adjusting it is pretty easy, and it
> >even allows you to not trigger motion on small objects like
> >brids etc, but do trigger when something bigger happens.
> 
> You can avoid noise by doing gradient based edge detection first and
> then subtracting.. that's exactly what I did in my program for video4linux.

Sure, but it all consumes CPU, the simple solution I depicted above
runs on old 486/33 machines with B/W parallel quickcams and has
CPU to spare for other things as well.

-Søren

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