[kwlug-disc] Image Comparison

[Richard Weait]

On Thu, Aug 13, 2009 at 2:54 PM, Chris Irwin<chris at chrisirwin.ca> wrote:
> (Sorry if this doesn't thread properly. I use IMAP via gmail and it
> doesn't echo my own mail back to me, so I can't actually reply to myself
> on-list.)

Looks okay here. ;-)

> I've got a bit of an update on my progress.

> On Tue, 2009-08-11 at 20:32 -0400, Chris Irwin wrote:
>> Does anybody know of any way of mass comparing jpeg files by a image
>> content rather than a file sum or name? I've got two sets of several
>> thousand images I need to sort through. Basically I want to find unique
>> files in directories A & B, deleting duplicates from B.
>
> Imagemagick has a utility called 'compare' that will take two images as
> input, and output a third image illustrating the difference (it seems
> to create a composite and overlay in red where they don't match).

[Fascinating Imagemagick results clipped.]
> I've now got something I can use in a script. Thanks to those who
> emailed me off-list with suggestions :)

That is pretty neat stuff, Chris.  Khalid's earlier post got me
thinking, "Why not use exif time / date / camera info as a clue that
two images came from the same source image?"  This way you can locate
and store sanely the original photo and the resized version, or the
original and the one that crops out Crazy uncle Richard....  Exif data
may find photos that are closely related but that vary wildly in pixel
count.

Best regards,
Richard.