Adding metadata alters (reduces) image file size.

Posted by on May 13, 2020; 4:30pm
URL: http://digikam.185.s1.nabble.com/Adding-metadata-alters-reduces-image-file-size-tp4712412.html

Good day, everyone!

I'm new to digiKam, and have been on the hunt for a non-destructive image organization tool.  This really seems to fit the bill quite nicely--what a great tool, thanks to all who have worked on it! :D

I had previously been looking at just utilizing File Explorer (Windows) to add tags to images, but I noticed that when I added tags to images, it would often reduce the filesize, also, sometimes quite a bit.  
Example:  12,365,692 bytes drops a meg to 11,247,905 bytes just after adding a single "test" tag!
I was not able to find any definitive data as to what exactly Windows is doing, here.  So I tried an experiment.

In digiKam, I would normally by looking at -not- saving data to the file (leaving those options unchecked).  But for a test, I enabled the saving of 'rating' to the file, and set a rating.  Sure enough, the filesize dropped by quite a bit, here, too.

Since this is contained to digiKam, I thought someone might be able to shed some light on what actual image manipulation is going on, here.  It is clearly doing something beyond just a few bytes of tag or rating data...

Thanks!