Lossless rotation of JPEG images in ShowImage

[ekdahl]

See mailing-list archive for the discussion on the subject: http://www.freelists.org/archives/openbeos/04-2006/msg00091.html

Here's Michael Lotz suggestion on how to implement it: http://www.freelists.org/archives/openbeos/04-2006/msg00183.html

The external command line app he mentions could e.g. be jpegtran (which is capable of many sorts of lossless operations on jpeg data) included in libjpeg.

[wkornewald]

Axel, didn't you implement that recently?

[ekdahl]

I think he made the translator take the EXIF orientation tag into account when opening images and passing on the EXIF info. I don't think that it solves this, i.e. doing the rotation of the image data lossless.

[axeld]

Exactly. I've written a small tool that allows writing back the ShowImage:orientation attribute as EXIF orientation for my own use (I might publish it on BeBits later). However, it doesn't know how to add EXIF data if there is none yet.

Since RAWTranslator and JPEGTranslator both export the EXIF data as part of the ioExtension message now, it would probably make sense to have an extra flag for Translate() (again, as part of the ioExtension) that would only update (or add) the EXIF data of/to a file.