Bug 509279

Summary: Why are some metadata updated "automatically" ?
Product: [Applications] digikam Reporter: Caro <caro.portal>
Component: Maintenance-MetadataAssignee: Digikam Developers <digikam-bugs-null>
Status: RESOLVED DUPLICATE    
Severity: normal CC: caulier.gilles, metzpinguin
Priority: NOR    
Version First Reported In: 8.7.0   
Target Milestone: ---   
Platform: Microsoft Windows   
OS: Microsoft Windows   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: Configuration

Description Caro 2025-09-08 16:25:34 UTC 
SUMMARY

I noticed that when I add a tag to a picture, several Metadata are changed, and I don't understand why.

For example, for a picture to which I added the Subject Party:
 
								Original								Updated
Composite:HyperfocalDistance		3.22 m								3.24 m
Composite:ScaleFactor35efl			4.4									4.3
ExifIFD:BrightnessValue			-5.454663662							-5.454663633
ExifIFD:ComponentsConfiguration	Y, Cb, Cr, -
ExifIFD:FlashpixVersion				100
ExifIFD:LensInfo					2.220000029-5.960000038mm f/1.6-2.2	2.220000029-5.96mm f/1.6-2.2
IFD0:YCbCrPositioning				Centered
QuickTime:MediaDataSize			1774314								1772898
System:FileModifyDate				2025:08:19 21:02:43+02:00				2025:08:21 18:11:09+02:00
System:FileName					IMG_2437_2.HEIC						IMG_2437.HEIC
System:FileSize					1810 kB								1809 kB
XMP-dc:Subject					Party
XMP-mwg-rs:RegionAppliedToDimensionsH	3024	
XMP-mwg-rs:RegionAppliedToDimensionsUnit	pixel	
XMP-mwg-rs:RegionAppliedToDimensionsW	4032	
XMP-mwg-rs:RegionAreaH			0.142523383	
XMP-mwg-rs:RegionAreaUnit		normalized	
XMP-mwg-rs:RegionAreaW			0.106892535	
XMP-mwg-rs:RegionAreaX			0.853608981	
XMP-mwg-rs:RegionAreaY			0.546550853	
XMP-mwg-rs:RegionExtensionsAngleInfoRoll	370	
XMP-mwg-rs:RegionExtensionsAngleInfoYaw	-41	
XMP-mwg-rs:RegionExtensionsConfidenceLevel	0	
XMP-mwg-rs:RegionExtensionsFaceID	1	
XMP-mwg-rs:RegionType			Face	

Discussing with the Exiftool team, it seems that this should not happen if using Exiftool update command simply.

STEPS TO REPRODUCE
1. Export metadata of a picture that was never manipulated using "exifTool -args -G1" command
2. Add a tag to a picture
3. Export metadata of a picture that was never manipulated using "exifTool -args -G1" command - notice all metadata that differ

OBSERVED RESULT
Several metadata related to the camera (lens, brightness...) are updated, while only a tag was added

EXPECTED RESULT
Only the tag should be added, other metadata should not change

SOFTWARE/OS VERSIONS
Windows: X

ADDITIONAL INFORMATION
Comment 1 Maik Qualmann 2025-09-08 16:45:01 UTC 
I can't reproduce it with a quick test here, using a JPG and HEIF file.
What are your exact metadata settings regarding reading and writing with ExifTool?
Please note that we're still working with Exiv2 and ExifTool uses a so-called EXV container for writing, so more metadata may be written than if you just add a keyword.
Reading with Exiv2 may result in a different interpretation/rounding of the values, which may then lead to changed Exif values ​​when writing back.

Maik
Comment 2 Caro 2025-09-08 19:19:37 UTC 
Created attachment 184822 [details]
Configuration
Comment 3 Caro 2025-09-08 19:21:09 UTC 
Hi Maik,

I have added a screenshot of my configuration and I have Exiftool 13.04 installed.

Here is the link to the picture I'm using for tests: https://we.tl/t-JJLqzkWryv

Thanks for your help !

Nice day,

C
Comment 4 caulier.gilles 2025-12-10 06:46:31 UTC 
Hi Maik,

Did you get the shared testing file from comment #3 ? File is not online anymore...

Gilles
Comment 5 Maik Qualmann 2025-12-10 08:41:50 UTC 
Hi Gilles,

The problem can sometimes be reproduced with any file, depending on certain metadata in the Rational format. Exiv2 rounds fractions differently than Exiftool. Since we write all the Exif metadata back using the EXV container, slight changes occur at the rounding level.

I don't see it as a critical issue. The only solution would be to write the metadata completely natively using Exiftool, writing only the changes that were actually made. I already have some ideas on how we could add this step by step for specific metadata.

Maik
Comment 6 caulier.gilles 2025-12-22 02:51:00 UTC 

*** This bug has been marked as a duplicate of bug 481755 ***