[gentoo-user] diff command for images

[gentoo-user] diff command for images

[Erik]

I need to find the difference between images (like the text-file diff
command, but for RGBA images). I tried "compare A.png A.png
difference.png". This should obviously produce some kind of blank image
because A.png and A.png are the same file, but for some weird reason the
produced difference.png has recognizable content! Is there a fix for
that bug or any other image diff program that is sane?
-- 
gentoo-user@lists.gentoo.org mailing list

Re: [gentoo-user] diff command for images

[Elias Probst]

[-- Attachment #1: Type: text/plain, Size: 712 bytes --]

Am Sonntag, 27. Januar 2008 14:54:15 schrieb Erik:
> I need to find the difference between images (like the text-file diff
> command, but for RGBA images). I tried "compare A.png A.png
> difference.png". This should obviously produce some kind of blank image
> because A.png and A.png are the same file, but for some weird reason the
> produced difference.png has recognizable content! Is there a fix for
> that bug or any other image diff program that is sane?

The easiest way for doing this, is using GIMP.
- Use one layer for each image
- Use the 'Subtract' mode for displaying the second layer

Regards, Elias P.

-- 
A really nice number:
"09:F9:11:02:9D:74:E3:5B:D8:41:56:C5:63:56:88:C0"

[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 189 bytes --]

Re: [gentoo-user] diff command for images

[Erik]

Elias Probst skrev:
> Am Sonntag, 27. Januar 2008 14:54:15 schrieb Erik:
>   
>> I need to find the difference between images (like the text-file diff
>> command, but for RGBA images). I tried "compare A.png A.png
>> difference.png". This should obviously produce some kind of blank image
>> because A.png and A.png are the same file, but for some weird reason the
>> produced difference.png has recognizable content! Is there a fix for
>> that bug or any other image diff program that is sane?
>>     
> The easiest way for doing this, is using GIMP.
> - Use one layer for each image
> - Use the 'Subtract' mode for displaying the second layer
>   
Not sure how to do this. I am not a graphic artist. But I just open it
with "gimp a.png b.png" and press Ctrl-C in one image, switch to the
other and press Ctrl-V. That seems to create a second layer. Then I have
no idea what to do.

A simple command would be useful. I might have to regression-test 1000
images in a svn commit because some of them seem to have been modified
by optipng.
-- 
gentoo-user@lists.gentoo.org mailing list

Re: [gentoo-user] diff command for images

[Jens Krahe]

Am Sonntag, 27. Januar 2008 schrieb Erik:
> I tried "compare A.png A.png difference.png". This should obviously produce 
> some kind of blank image
> because A.png and A.png are the same file, but for some weird reason the
> produced difference.png has recognizable content!
Try "compare -metric AE A.png A.png difference.png"
This gives you the absolute number of diffrent pixels.

http://www.imagemagick.org/script/command-line-options.php#metric

Regards
Jens
-- 
gentoo-user@lists.gentoo.org mailing list

Re: [gentoo-user] diff command for images

[Willie Wong]

On Sun, Jan 27, 2008 at 02:54:15PM +0100, Penguin Lover Erik squawked:
> I need to find the difference between images (like the text-file diff
> command, but for RGBA images). I tried "compare A.png A.png
> difference.png". This should obviously produce some kind of blank image
> because A.png and A.png are the same file, but for some weird reason the
> produced difference.png has recognizable content! Is there a fix for
> that bug or any other image diff program that is sane?

It seems that you do not understand how the compare function works
http://www.imagemagick.org/script/compare.php

The output image is the second image overlaid with a red "mask". The
pixels that are tinted red in the output shows the pixels that differ
from the original one. The ones that are not tinted red are unchanged.
So if you compare A to A, you will get something that looks like A
tinted by white.

What you want is something like

composite A.jpg -compose minus A.jpg Out.jpg

Look at
http://www.imagemagick.org/script/command-line-options.php#compose

to see what composite operators you can use for doing the comparison. 

W
-- 
Heineken (/hnkt/)... since the second millennium B.C., middle kingdom.
           ' '
Sortir en Pantoufles: up 415 days, 16:27
-- 
gentoo-user@lists.gentoo.org mailing list

Re: [gentoo-user] diff command for images

[Ralf Stephan]

You could also try the pamarith comand of the netpbm package.
It has both -subtract and -difference


ralf
-- 
gentoo-user@lists.gentoo.org mailing list