How to compare 2 images from command line

Polytropon freebsd at
Tue Sep 2 15:40:48 UTC 2008

On Tue, 02 Sep 2008 11:31:49 -0400, FreeBSD <freebsd at> wrote:
> I want to determine if Mplayer is working correctly. The best way to be 
> sure is to check if the display on the screen is changing. That's the 
> purpose of the screenshots.

And this works? I always thought mplayer would output the video
stream via DRI / DRM, so on the screenshot, nothing would be seen...

> The screenshots are taken by Nagios every 5 
> minutes and the new screenshot is compared with the preceding one. But, 
> by now, it doesn't work because every tool we try is seeing a diffence 
> between 2 identical images.

The images may be identical in content, but it's completely possible
that other data (others than the pictural information) is coded into
the file, for example date and time of creation, so the files may be
different, while the pictures they show are identical.

It would be useful first to "decompile" the files - create a new file
that only contains pictural information, nothing more.

>From Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

More information about the freebsd-questions mailing list