Re: [Boost-users] [GIL] rotated90cw_view - jpeg lossless rotation

Christian Henning wrote:

Hi Jose, please see comments below.

On Sun, Dec 6, 2009 at 5:10 AM, Jose wrote:

...

I rotate jpeg photos to portrait by reading the file and saving it like this:

boost::gil::jpeg_write_view(file, boost::gil::rotated90cw_view(boost::gil::view(img)));

results:

original size: 4106172 image/jpeg 3264 2448 rotated size: 5594681 image/jpeg 2448 3264

The rotation should be lossless (as the image is a multiple of the jpeg MCU) but the size has increased significantly and the exif tags disappeared.

I think libjpeg has a way of applying lossless transformations while reading it. Is that correct, or am I mistaken here?

JPEG lossless transformation is a trick performed on the compressed JPEG data (IIUC, you basically shuffle the values in each block), and can therefore not be achieved by using a generic image library that provides a JPEG reader and writer. You need specialized functions that operate on the compressed JPEG data. Sebastian