How to compare 2 images from command line
freebsd at optiksecurite.com
Tue Sep 2 15:58:22 UTC 2008
Bill Moran a écrit :
> In response to FreeBSD <freebsd at optiksecurite.com>:
>> Andrew Gould a écrit :
>>> On Tue, Sep 2, 2008 at 10:23 AM, FreeBSD <freebsd at optiksecurite.com
>>> <mailto:freebsd at optiksecurite.com>> wrote:
>>> Tom Marchand a écrit :
>>> Hash the images and compare the hashes.
>>> -------------- Original message ----------------------
>>> From: FreeBSD <freebsd at optiksecurite.com
>>> <mailto:freebsd at optiksecurite.com>>
>>> Hi everyone,
>>> I'm trying to determine if 2 jpeg images are identical. The
>>> images are screenshots taken with scrot at different times.
>>> The point is to know if the display is working correctly. I
>>> tried to use 'diff' but without success, probably because of
>>> the metadata included in the image. I also tried the
>>> 'compare' command from imagemagick, but it produce an image
>>> containing the difference between the 2 images instead of
>>> telling me if both images are identical.
>>> So, my question is what are you using to determine if 2
>>> images are identical?
>>> I'm using FreeBSD 7.0 and I need to be able to script this
>>> comparaison for an integration in Nagios.
>>> Thank you,
>>> I just tried it and it doesn't work. The hashes are different. I can't
>>> say that I'm surprised since 'diff' is "seeing" a difference between the
>>> two identical images.
>>> Thanks for the suggestion
>>> Yes, there's a huge difference between testing differences in images and
>>> testing differences in files. What do you mean by "...know if the
>>> display is working correctly."?
>> 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. 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.
> Can you put the screenshots into some other format? As you mentioned,
> the jpeg format includes metadata, which might include the creation
> time and would cause every image to be unique from a filesystem view.
> For example, I don't believe bitmaps include metadata, which would cause
> them to be identical if the display were identical.
Thank you! It did the trick. I just converted the image from png (sorry
it wasn't jpeg...) to bmp and it works with cmp. Even diff now recognize
both images as identical.
Thanks everyone for your support.
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