Since it is my first post on this forum, I want to congratulate the authors of XnView. This is really a wonderfull software
Now I will share with you my own experience:
-I have a Sony Alpha 700
-output picture size is 2848x4272
-when I use "JPEG Lossless transformation"/"Rotate based on EXIF value", file size always decreases of about 500ko
-I tried other softwares to do this operation (e.g. JPEG Lossless Rotator http://annystudio.com/software/jpeglosslessrotator/
) with exactly the same results
On the web (like on this post), I saw everywhere that if the picture dimensions are multiple of 16, the rotation is really lossless.
This is the case of my pictures: 2848/16=178 and 4272/16=267
Thus, "why is the file siez smaller?"
After reading the wonderfull JPEG tutorial of ImpulseAdventure http://www.impulseadventure.com/photo/j ... ssion.html
, I installed JPEGsnoop (http://www.impulseadventure.com/photo/jpeg-snoop.html
This tool explores a JPEG file and exposes all details of its compression.
I compared 2 JPEGsnoop logs: the fisrt coming from a camera picture and the second coming from the 'XnView rotated' picture
Among all compression details, the main difference I discoveredis this section that exists only on the fisrt log:
*** Additional Info ***
NOTE: Data exists after EOF, range: 0x002CBB6D-0x003492AF (513858 bytes)
I still don't know what are these "Data after EOF" (probably some Sony's metadata), but it seems that they are dropped during the lossless operation.
I am reassured: the rotation is not so "lossless" but it doesn't decrease the quality of the picture.
I hope that it can help someone else.