@Kris
OK, I have now done the stated procedure on an own example, and I can confirm:
The JPEG rotation in DOpus is LOSSLESS and works correctly!
Please post an example which you think would not work so that we can analyze what is wrong there.
There are some flaws in your statements:
-
JPEG lossless rotation is not done on pixel data.
That's why I carefully wrote "Lossless rotation of JPEG data" above, which is internally represented as DCT (Discrete Cosine Transform) coefficients.
See also my post in the Force lossless rotation of JPEGs thread. -
Just modifying the Orientation metadata is not the preferred method.
This is a dumb method, and Windows is a dumb OS regarding JPEG support, as I have explained in other places.
Other than many other compressed image formats, JPEG can adjust the orientation losslessly by rearranging DCT coefficients, so decoders need not be burdened with the task.
See also my posts in above given thread.
Regards
Guido
JPEG developer