[vox-tech] .jpg Mystery

[Carl Boettiger]

On Thu, Jan 21, 2010 at 11:41 AM, Rod Roark <rod at sunsetsystems.com> wrote:

> On 01/21/2010 11:18 AM, Bill Kendrick wrote:
> > On Thu, Jan 21, 2010 at 10:35:35AM -0800, Bob Scofield wrote:
> >> In Linux there are a couple of different ways I can get the date and
> time the
> >> photo was taken.
> >
> > I picked a random photo I took with a Canon digital camera a few years
> ago.
> > The date/timestamp of the file on my laptop was from 9:05pm on the day
> > the photo was taken.
> >
> > However, using "File->Properties..." in Gwenview, and looking at the
> > metadata stored in the file itself, it was stamped as 8:05pm of that day.
> >
> > I'm guessing the timestamp in the metadata is off by an hour because
> > I never adjusted the clock inside my camera to account for Daylight
> Savings
> > time change.  (In other words, the camera THOUGHT it was 8:05pm, so
> that's
> > the metadata it stored.)
>
> I would think that the file's timestamp is derived from the time set in
> the camera, one way or another.  Either the camera creates the file on a
> standard (probably win32) filesystem when the picture is taken, or the
> timestamp is assigned from the metadata by some special software that
> fetches images to your computer from the camera.
>
> Sounds like some sort of bug to me, perhaps where some piece of software
> neglects to take DST into account.
>

Sounds plausible to me.  Digital cameras attach metadata in an EXIF file,
the exiv2 will let you read this file directly:
http://www.exiv2.org/sample.html  Perhaps the machines.software interpret
this file differently (i.e. DST stettings))
Of course there's lots of reasons a timestamp won't match reality:
http://www.slate.com/id/2140303/


-Carl

>
> Rod
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-- 
Carl Boettiger
Population Biology, UC Davis
http://two.ucdavis.edu/~cboettig
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