Time Date based rename

[Mick Sulley]

Is there ant way to set the rename function when importing pictures to
base it on the datetime original?  I have setup the import based upon
[date] but with my Canon EOS 550D this does an automatic one hour
adjustment.  There is no setting on the camera for daylight saving, so I
don't know why it does the adjustment.  My Canon SX200 does have a
timezone setting and that uses datetime original as I would expect.  I
cannot see any way to set which one is used.
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[Peter Albrecht]

Hi Mick,

I have a Canon EOS 500D and I manually adjust the camera
time twice a year. It is anoying, but I haven't found
another way.
Importing those pictures, I have a correct EXIF time in digikam.

Regards,
        Peter

On 23.10.2013 18:10, Mick Sulley wrote:

> Is there ant way to set the rename function when importing
> pictures to base it on the datetime original?  I have setup
> the import based upon [date] but with my Canon EOS 550D this
> does an automatic one hour adjustment.  There is no setting
> on the camera for daylight saving, so I don't know why it
> does the adjustment.  My Canon SX200 does have a timezone
> setting and that uses datetime original as I would expect.
> I cannot see any way to set which one is used.
> _______________________________________________
> Digikam-users mailing list
> [hidden email]
> https://mail.kde.org/mailman/listinfo/digikam-users
>

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[Mick Sulley]

Hi Peter,

Thanks for the reply.  Yes I see that as well, the exif data shows the same time as the camera, the thing I don't understand is that DigiKam renames the picture on import as one hour later than the exif date.  e.g. - from the info panel on the right

File Properties
PIC2013_1013_161516.JPG
Date 13/10/2013 16:15:16

Photograph Properties
Created 13/10/2013 15:15:15

exif Image Information
Date and Time 2013:10:13 15:15:15

exif Photgraph Information
Date and Time (original) 2013:10:13 15:15:15
Date and Time (digitized) 2013:10:13 15:15:15

If I take this same picture and run
exiftool "-FileName<DateTimeOriginal" -d "PIC%Y_%m%d_%H%M%S.%%e" .
it renames it as PIC2013_1013_151515.JPG just as I expected.

Why does DigiKam move it by an hour?????

Our clocks go back to GMT at the weekend, I will be interested to see if that changes anything.

Regards
Mick

On 25/10/13 19:22, Peter Albrecht wrote:

Hi Mick,

I have a Canon EOS 500D and I manually adjust the camera
time twice a year. It is anoying, but I haven't found
another way.
Importing those pictures, I have a correct EXIF time in digikam.

Regards,
	Peter

On 23.10.2013 18:10, Mick Sulley wrote:

Is there ant way to set the rename function when importing
pictures to base it on the datetime original?  I have setup
the import based upon [date] but with my Canon EOS 550D this
does an automatic one hour adjustment.  There is no setting
on the camera for daylight saving, so I don't know why it
does the adjustment.  My Canon SX200 does have a timezone
setting and that uses datetime original as I would expect. 
I cannot see any way to set which one is used.
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[Jean-François Rabasse-2]

On Fri, 25 Oct 2013, Mick Sulley wrote:

> Hi Peter,
>
> Thanks for the reply.  Yes I see that as well, the exif data shows the same
> time as the camera, the thing I don't understand is that DigiKam renames the
> picture on import as one hour later than the exif date.  e.g. - from the
> info panel on the right
>
>       File Properties
>       PIC2013_1013_161516.JPG
>       Date 13/10/2013 16:15:16
> ...
>       exif Photgraph Information
>       Date and Time (original) 2013:10:13 15:15:15
>       Date and Time (digitized) 2013:10:13 15:15:15

Hi Mick,

These datetime issues are often a nightmare and will go on being.
This because of a major weakness in the Exif standard and unaccurate
specifications on how to process time by application programs.

The Exif standard has provided fields for datetime stamps, but has
forgotten the time reference, too bad:-(
The standard fields have a fixed length of 19 ascii characters and
can accomodate things like "2013:10:13 15:15:15", nothing more.

Some camera manufacturers implement extra information, the time
zone and the daylight savings flags, but this is not standard Exif
and has to be stored in the Maker notes part of the Exif section.
Application programs may, or not, decode and use.

Note that this information is only informational and it's up to the
user to ensure consistency in the camera setup. It doesn't work like
a computer where you can set the hardware clock to UTC, then
specify you living time zone and daylight savings, and the operating
system will use all that and rebuild a valid local time.

In a camera, the datetime field is supposed to be ... a date, and
application programs are allowed to assume it's a local time.
The problem is this is not correctly defined. E.g. when referencing
to the XMP standard (XMP is expected to handle valid dates in ISO
8601 format, i.e. things like "2013:10:13 15:15:15+01:00" (this in
your case, time zone Greenwich, daylight savings active).
but the standard says :
  « If no time zone is contained in the EXIF, convert to XMP assuming
    a local time. »

A local time ! Which local time ? The local time at the moment the
camera took the picture, or the local time on the computer reading
the image ? No one knowns. And software do more or less what they
want. This is why you get different results with exiftool or with
Digikam which uses the exiv2 library.
Exiftool may decide to use the Exif timestamp as a neutral template
and Digikam/libexiv1 may decide to adjust from your computer daylight
savings, thus giving + 1 hour.
(Try again tomorrow :-)

Also, neither exiftool nor libexiv2 produces correct dates when encoding
XMP sidecar files, the fractional part of seconds is added but the time
zone offset is missing.

This is a real problem when geotagging images from a GPS tracks log,
where the UTC time of the image is required for correlation.
And correlation programs provide a time shift option to let the user
adjust when the results are silly.
Similar problems for people that travel, take a photo before boarding
a plane and look at the photo once back home, maybe a couple of hours
"before" :)

Anyway, the best way is probably to maintain cameras datetime to the
user localtime, i.e. what's shown by your wrist watch.
I totaly agree with Peter saying « I manually adjust the camera time
twice a year ».
I do the same, adjust the time AND toggle the daylight savings mode,
this to keep the information for future (i.e. programs able to
process a correct time from all the information).

An alternative is to have a camera with a GPS device, giving a valid
UTC timestamp at the moment the picture is shot, be you at home or
in Japan or Australia.

Cheers,
Jean-François

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[Mick Sulley]

Firstly many thanks Jean-François for the very comprehensive reply, I now have a better understanding of the issue, just need to decide how to manage it:)

My main camera is a Canon EOS 550D, which does not have a setting for time zone or daylight saving.

Now we are back on good old GMT I have tested again, and now the date is consistent in all fields and the file is renamed to the expected time and date.  So this means  that somehow DigiKam (or possibly my computer) decides that during BST the time on exif is GMT an renames the picture to an hour later to make it BST.  So if I always leave my camera set to GMT the pictures will show as the expected time when I import them into DigiKam.

Regards
Mick

On 26/10/13 18:53, Jean-François Rabasse wrote:

On Fri, 25 Oct 2013, Mick Sulley wrote:

Hi Peter,

Thanks for the reply.  Yes I see that as well, the exif data shows the same
time as the camera, the thing I don't understand is that DigiKam renames the
picture on import as one hour later than the exif date.  e.g. - from the
info panel on the right

      File Properties
      PIC2013_1013_161516.JPG
      Date 13/10/2013 16:15:16
...
      exif Photgraph Information
      Date and Time (original) 2013:10:13 15:15:15
      Date and Time (digitized) 2013:10:13 15:15:15

Hi Mick,

These datetime issues are often a nightmare and will go on being.
This because of a major weakness in the Exif standard and unaccurate
specifications on how to process time by application programs.

The Exif standard has provided fields for datetime stamps, but has
forgotten the time reference, too bad:-(
The standard fields have a fixed length of 19 ascii characters and
can accomodate things like "2013:10:13 15:15:15", nothing more.

Some camera manufacturers implement extra information, the time
zone and the daylight savings flags, but this is not standard Exif
and has to be stored in the Maker notes part of the Exif section.
Application programs may, or not, decode and use.

Note that this information is only informational and it's up to the
user to ensure consistency in the camera setup. It doesn't work like
a computer where you can set the hardware clock to UTC, then
specify you living time zone and daylight savings, and the operating
system will use all that and rebuild a valid local time.

In a camera, the datetime field is supposed to be ... a date, and
application programs are allowed to assume it's a local time.
The problem is this is not correctly defined. E.g. when referencing
to the XMP standard (XMP is expected to handle valid dates in ISO
8601 format, i.e. things like "2013:10:13 15:15:15+01:00" (this in
your case, time zone Greenwich, daylight savings active).
but the standard says :
 « If no time zone is contained in the EXIF, convert to XMP assuming
   a local time. »

A local time ! Which local time ? The local time at the moment the
camera took the picture, or the local time on the computer reading
the image ? No one knowns. And software do more or less what they
want. This is why you get different results with exiftool or with
Digikam which uses the exiv2 library.
Exiftool may decide to use the Exif timestamp as a neutral template
and Digikam/libexiv1 may decide to adjust from your computer daylight
savings, thus giving + 1 hour.
(Try again tomorrow :-)

Also, neither exiftool nor libexiv2 produces correct dates when encoding
XMP sidecar files, the fractional part of seconds is added but the time
zone offset is missing.

This is a real problem when geotagging images from a GPS tracks log,
where the UTC time of the image is required for correlation.
And correlation programs provide a time shift option to let the user
adjust when the results are silly.
Similar problems for people that travel, take a photo before boarding
a plane and look at the photo once back home, maybe a couple of hours
"before" :)

Anyway, the best way is probably to maintain cameras datetime to the
user localtime, i.e. what's shown by your wrist watch.
I totaly agree with Peter saying « I manually adjust the camera time
twice a year ».
I do the same, adjust the time AND toggle the daylight savings mode,
this to keep the information for future (i.e. programs able to
process a correct time from all the information).

An alternative is to have a camera with a GPS device, giving a valid
UTC timestamp at the moment the picture is shot, be you at home or
in Japan or Australia.

Cheers,
Jean-François

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[Jean-François Rabasse-2]

On Mon, 28 Oct 2013, Mick Sulley wrote:

> My main camera is a Canon EOS 550D, which does not have a setting for time
> zone or daylight saving.
>
> Now we are back on good old GMT I have tested again, and now the date is
> consistent in all fields and the file is renamed to the expected time and
> date.  So this means  that somehow DigiKam (or possibly my computer) decides
> that during BST the time on exif is GMT an renames the picture to an hour
> later to make it BST.  So if I always leave my camera set to GMT the
> pictures will show as the expected time when I import them into DigiKam.

Hi Mick,

Lucky guy, sitting on the Greenwich meridian :-)

Well, your trick may work but will still remain software dependent.
As you said in your former e-mail, you saw the problem with Digikam
but not with exiftool.
And if you leave your camera clock on UTC+0, even in summer, some
software (e.g. web albums managers) may stamp your images with a one
hour shift.

As I said, there's no perfect solution to this issue. It's too late,
except if in a future a major release of the Exif standard does take
the problem in account.

A common good solution (or less bad) is what Peter Albrecht said,
adjusting the camera time twice a year to reflect the common local
time. As for me that's what I do, even when I happen to travel;
I prefer have my camera always showing home time, and I sometime take
a shot of any wall clock upon arrival in an airport. Then issue
corrections later, once back home.

But anyone can build personal modus operandi.

Regards,
Jean-François
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