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There's no zone information in the capture timestamp. Why?

6

CIPA DC- 008 is the standard for Exif 2.2. Of note it makes no mention of "timezone." "GMT" is also not mentioned either. The term "UTC" does appear but only specifies the GPS time is recorded as such. Pedants may note that this is slightly misleading since GPS time is not identical to UTC

My point, in short, is that omission of timezone is likely not accidental. I'm not saying that CIPA or JEITA thought it was a good idea to leave timezone out. I have no way of knowing how they felt about the decision. The fact that UTC is specified in one time tag and not in another means that the creators of the standard were aware they were leaving it out.

I can't say for sure but I am willing to speculate that usually when something is ambiguous in a standard it is because of a disagreement in the committee that created it. I suspect that unless somebody unearths the transcript of the discussions around creation of EXIF we will never really know why.

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EXIF v2.31 (p49) defined time-zone offset fields in 2016 and the XMP time-zone guidelines (p33-34) also consider time-zones. The implementation in cameras and programs is rather minimalist at the moment.

See also my answer to an older question: What do you do with your camera clock time in relation to time zones?

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    I upvoted this answer because it cites what sound like fairly authoritative articles, but, unfortunately, the XMP timezone guidelines link is currently broken. – Michael Scheper Jun 23 '19 at 10:18
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    @MichaelScheper, seems like the whole website of MWG is down. Hard to find out what happened to them. Metadata anarchy, here we come... – aXeL-HH Feb 28 at 11:22
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    I've updated the link to EXIF v2.31 (pending approval). This should be the selected answer these days, given that new cameras are actively using the new time zone fields. – lxgr Apr 8 at 7:55
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Look at a Time Zone map. Time Zones are local political decisions, not necessarily agreeing with simple 15 degree longitude lines. For GPS to get it correct, the camera would have to have extensive lists including everywhere time zone did not map to longitude. Our computers and our cameras can't know this, and don't try to deal with that, they simply ask which time zone we want to show.

Knowing GMT is a lot to know, but we can set our camera to show whatever time zone we wish.

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    The OP didn't ask why the camera doesn't determine time zone from GPS data, they asked why the time zone isn't recorded in the EXIF data. Many cameras let the user enter time zone along with the date and time; including that information in the EXIF info would presumably be pretty simple. – Caleb Feb 19 '18 at 5:39
  • Time Zone is Not an observable feature, a difficulty of course assumed to apply to GPS satellites too. :) – WayneF Feb 19 '18 at 14:51
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    It's exactly as observable as Artist and Copyright, two other values that the user sets. – Caleb Feb 19 '18 at 15:46
  • Exactly, that was my point too. The user can set whatever Time Zone they want to see, but it is not otherwise detectable by external direct observation. That's what makes it difficult to add to Exif too. Yes, I did err in assuming GPS timestamp, since of course we do know our own Time Zone, but Time Zone can confuse it when traveling. – WayneF Feb 19 '18 at 16:54
  • Actually, it seems that Google Photo, and sometimes Facebook, tries to infer timezones from geodata, and assumes that the EXIF time is in that timezone. That's my best guess for why it seems to mess up the timestamps so badly, anyhow, since I try to keep EXIF timestamps UTC. – Michael Scheper Jun 23 '19 at 10:21

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