On changing timestamps and timezones in jpg's and RAF raw files.

Started by ewijburg, March 08, 2017, 11:22:20 PM

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ewijburg

I'd like some feedback on the "do's and don'ts" regarding changing the timestamp and timezone on my pictures.

The problem I'm trying to tackle is the following:

Past three weeks I made pictures in Chile. My camera was set to Central European Summer Time (UTC +2 / GMT +2). This means a time mismatch of -5 hours.
I shot my photo's on a Fujifilm X-T1, jpg + raw. The files were imported in a "sorting" folder to be able to batch correct for titles, headlines etc. But also to correct the time.

Using the "modify EXIF date and time" tool on one picture with a jpg and a RAF version (using the time shift option) I noticed that only the jpg is altered.
If I am reading the helpfiles and the forum correctly this is because for RAF files "write EXIF" and "write IPTC" are turned of in the standard options for this file format in the metadata2 preferences. Since they are turned on for cr2 files I take it that for this Canon raw format it is considered safe but not for the propriatary (non documented) RAF format?
That the RAF doesn't show a change is because only the xmp sidecar file is altered, but re-alterd with the old embedded EXIF date in the RAF file?

Apart from this issue I think that I understand that the correct time format for a picture taken on march 8th 2017 in Chile at 17:00 chilean local time would be: 08032017 17:00:00 -03:00 (Chilean daylight savings time is UTC -03:00).
A photo taken in Germany on the same day and same local time would be: 08032017 17:00 +01:00
A photo taken in Greenwich (same day and same local time): 08032017 17:00 00:00.

I temporarily altered the file format options for RAF to allow "write EXIF" and "write IPTC". Then I tried a timeshift on one RAF file. The file seems to stay OK.

From this n=1 test I think that my workflow should now be as follows:

1. allow writing of "write EXIF" and "write IPTC" on RAF files (at least temporarily for the processing of timestamps of these holiday pictures).
2. in the metatdata 2 tab change XMP and IPTC timezone to -03:00.
3. Use the "modify EXIF date and time" command to shift the timecreated / digitized -5 hours (the timedifference between Central European Summer Time [as set in my camera] and ChiLean Summer Time).
4. Change the XMP and IPTC timezone back to "local timezone" or +01:00 [for my situation] in metadata2.
5. Re-enable standard fileformat preferences for RAF files (*not* to allow "write EXIF" and "write IPTC").


Am I correct?

Mario

ExifTool is considered to the 'safe to use' for all file formats for which it supports write-back (including RAF). ExifTool is used by millions of people every day, and works behind the curtain in many applications. I never had a damaged file because of ExifTool. ExifTool is very picky and when it finds something in a file that it does not understand, it does not change the file.

The options to disable write-back for RAW files are for the users who don't want to touch their RAW files ever. With the consequences that they are pretty limited in what they can do to metadata. If you don't let IMatch write your RAW files, you also have to disable the EXIF-IPTC-XMP mapping, else IMatch only updates the sidecar, and when the file is re-imported the embedded and unchanged metadata in the file 'comes back' and overrides the XMP data.

Most traveling photographers I know keep their cameras on UTC, because this avoids any time-zone related troubles.
EXIF does not know a thing about time zones. Legacy IPTC does. And XMP of course. I explain the consequences of this in detail in the corresponding help topic.
-- Mario
IMatch Developer
Forum Administrator
http://www.photools.com  -  Contact & Support - Follow me on 𝕏 - Like photools.com on Facebook

ewijburg

Thank you, Mario, for your quick reply. You've confirmed that I'm on the right track.

Quote from: Mario on March 09, 2017, 08:13:14 AM
ExifTool is considered to the 'safe to use' for all file formats for which it supports write-back (including RAF). ExifTool is used by millions of people every day, and works behind the curtain in many applications. I never had a damaged file because of ExifTool. ExifTool is very picky and when it finds something in a file that it does not understand, it does not change the file.

The options to disable write-back for RAW files are for the users who don't want to touch their RAW files ever. With the consequences that they are pretty limited in what they can do to metadata. If you don't let IMatch write your RAW files, you also have to disable the EXIF-IPTC-XMP mapping, else IMatch only updates the sidecar, and when the file is re-imported the embedded and unchanged metadata in the file 'comes back' and overrides the XMP data.

I seem to remember from an earlier reply of yours in another topic (probably years older) that you warned against writing to RAF files.
In my version of IMatch (5.6.22 with ExifTool 10.19) EXIF write and IPTC write are standardly turned of for *.raf while standardly allowed for *.cr2 files. Thus I presumed that you deemed raf files unsafe to modify. Might I suggest to state that this isn't so more explicitly in the blue box in the changing date and time help topic (were this is implied in so many words but not explicitly stated [ I'd be glad to write it up, if you want])?

Quote from: Mario on March 09, 2017, 08:13:14 AM
Most traveling photographers I know keep their cameras on UTC, because this avoids any time-zone related troubles.
EXIF does not know a thing about time zones. Legacy IPTC does. And XMP of course. I explain the consequences of this in detail in the corresponding help topic.

I think that I too will change my camera clocks to UTC. However I will probably stick to storing the shooting location local time + timezoneoffset in IMatch (I'm lazy and don't want to do the math in my head to calculate the time the photo was taken on location   :) )

Thank you again,

Edwin.

Mario

I'm not sure anymore why .ref is not enabled by default. I think I have enabled only common formats three years ago when I created these defaults.

RAW files are undocumented and Sony has created dozens of variations over the years. If I could I would remove all EXIF data, IPTC and GPS from RAW files. And keep only one standard set of data in XMP. EXIF was created 30 years ago, when digital cameras had 1 megapixel. Yet still the camera vendors use it. Not one of the big vendors did the clever thing and swapped out all the old junk in favor of a modern, safe and portable XMP record.
-- Mario
IMatch Developer
Forum Administrator
http://www.photools.com  -  Contact & Support - Follow me on 𝕏 - Like photools.com on Facebook