[Digikam-users] Is jpeg rotation loseless?

[Marcel Wiesweg]

> > > And how can I tell when I use the image editor rotating feature and
> > > when the feature from a KIPI plugin? The rotation I can do from a
> > > thumbnails context menu. Is this done by a plugin or by the image
> > > editor?
> >
> > By a kipi plugin.
>
> So can you take it the way that every rotation that is not done by "left
> click on an image -> transformations -> rotate" is loseless?

Remove the "not".

You are using the image editor if you have opened the image in the image 
editor, rotated, and clicked on save. The image editor is operating on raw 
RGB data, and rotating there is no difference to applying any effect, it's 
changing pixels. It can load from a variety of image formats, not only JPEGs, 
it works on raw data, and it can save back to a variety of formats, some of 
them are lossless (PNG, TIFF), but JPEG is not lossless.

Lossless rotation is a special feature of the JPEG compression format, at a 
level above raw image data.

Marcel