JPG filesize changes during import with autorotate ON

[Maik Qualmann]

The modification date does not change here under Linux. It shouldn't change 
either because we copy the modification date.
The difference in size between rotated images has often been discussed. 
Remember that lossless rotation always creates a completely new image. There 
are no image losses if the rotation can be performed without loss. You can 
specify in the digiKam settings that if lossless rotation cannot be carried 
out, lossy rotation will take place or not.
Let's assume that camera images can usually be rotated without loss. All 
metdata is also copied from the original image to the new image. This can lead 
to a significant reduction in file size. Many camera manufacturers use padding 
areas between metadata (probably for performance reasons). ExifTool packages 
all metadata together. There is also an FAQ about this at ExifTool.

https://exiftool.org/faq.html (see 13a)

Maik

Am Samstag, 11. Mai 2024, 16:46:50 MESZ schrieb digikam at boeziek.nl:
> Hello,
> 
> I am new to Digikam and used an existing Lightroom/CaptureOne
> photo/filestructure with Digikam and imported those by adding a folder as a
> collection without any issues. Very promising app, thanks for all the hard
> work!
> 
> Background: I run MacOS 14.4.1 (latest) and Digikam 8.3. I shoot RAW + JPG
> on a Fujiflm X-T2.
> 
> Yesterday I started importing photos from an SD Card into Digikam, using
> "adding photos" as the USB didn't recognize my USB slot in my Thunderbolt
> Pro Dock.
> 
> When I select auto-rotate/flip ON, I notice that all my JPEG's are changed.
> Not only those that are rotated, but all of them have a new modification
> date in Finder.
> 
> For the rotated ones, I also noticed the file sizes are reduced. E.g. a
> 12.1MB JPEG on my SD card became 11MB after import on my disk or a 11.5MB
> became 10.4MB. So over a megabyte is trimmed, some are only reduced by
> 100KB.
> 
> Is that normal behaviour? Are all the JPEG's re-encoded during import? If
> so, doesn't that mean you start losing quality as rewriting JPGs is not
> recommended?
> 
> When I turn off the auto-rotate, then all files are imported unchanged.
> 
> Thanks,
> 
> Etienne