[Digikam-users] Is jpeg rotation loseless?

[Florian Lindner]

Am Sonntag, 11. Juni 2006 19:48 schrieb 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".

"left click on image" opens the image editor. So I guess my statement is 
correct, isn't?
As soon as I enter the image editor I perform lossy changes. 
Right click -> rotate or "Picture Menu" -> Rotate is loseless. Correct?

Regards,

Florian

>
> 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
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