Digikam-users Digest, Vol 241, Issue 8

[Remco Viëtor]

On mercredi 11 juin 2025 09:54:08 heure d’été d’Europe centrale Steve Franks 
wrote:
> SF- When software rotates an image it has to unpack the jpeg, rotate the
> image which may lose a few bytes, then recreate the jpeg. (...)
Well, not always...
Jpegs *can* be rotated over (multiples of) 90° without any need to re-encode 
the image, so without any extra loss (some limitations apply). See e.g. 
https://www.guyrutenberg.com/2016/04/22/jpeg-rotation/, which also mentions 
Digikam, btw.

Or a program can just set an EXIF tag, which then should be interpreted by the 
viewing program (or editor). Also lossless...

But that won't work if you use the Digikam *image editor* to do the rotation 
(as an editor, it needs to decode the jpeg for its operation. So that decoding 
is done at startup.)

Remco