Ühel kenal päeval, E, 2010-09-13 kell 17:57, kirjutas Tim: > On 10 September 2010 01:13, Mattias Põldaru <[email protected]> wrote: > > JPG files can contain EXIF data, which specifies it's orientation. This > > is good, because JPEG is lossy format and every time you reencode it, > > you loose some information. Doing real rotate in file is not possible > > without reencoding. > > The problem is, not all software can handle EXIF rotate right. But GIMP > > can, it asks on opening, whether to rotate the image or not (since it > > has to reencode it anyway). > > Apparently this isn't so. jpegtran (in package libjpeg-progs in > Ubuntu/Debian) has a lossless rotator (plus a few other functions). > > From the man page. > > jpegtran works by rearranging the compressed data (DCT coefficients), > without ever fully decoding the image. Therefore, its transformations > are lossless: there is no image degradation at all, which would not be > true if you used djpeg followed by cjpeg to accomplish the same conver‐ > sion. But by the same token, jpegtran cannot perform lossy operations > such as changing the image quality. > > More information should be at http://jpegclub.org/ > I believe not every JPEG can be rotated in this fasion, but a good > number can be. > > Personally, I prefer if the camera ether rotates it, or the final > viewing software rotates it. But maybe an option at import time to > rotate images would be good? My old camera import script would run all > my photos through exiftran which does the same lossless rotations as > jpegtran but also updates the exif information to reflect the rotation > (and got the rotation direction from the exif). > http://linux.bytesex.org/fbida/ for exiftran > > Tim > Thank you for clarification. I really didn't know about jpegtran. Would you file a feature request for this? Such an option on importing from camera sounds reasonable (this would also need removing the EXIF rotation information). I hope developers agree :)
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