Quote:
Unfortunately, you can't use file size as a test to see if the transform was done losslessly.


You kind of can actually:

- use XP picture viewer to rotate through 90 degrees
- close XP picture viewer
- note the new file size
- use XP picture viewer to rotate back and forth through 90 degrees a few times (closing it each time you rotate)
- at the end rotate back to the position you first rotated it to
- note the finishing file size

If the file size after the first rotation and the last are the same then you can be pretty sure that it is rotating losslessly. I've just done this and it would appear to be rotating losslessly, which is a surprise.

If it wasn't rotating losslessly then the file size would change and more and more rotations were applied.
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