On Wednesday 29 January 2003 02:38 pm, Pieter Eendebak wrote:

- If I do a rotation in the Gimp on a jpeg file will the rotation be

lossless

(for 90 degree rotations)?

I think you're actually asking the wrong question: A 90-degree rotation should be lossless, but you can't rotate a "jpeg" in Gimp, you rotate a "Gimp image". You already converted the jpeg to a gimp image when you loaded it, and you will convert it back to a jpeg when you save it (with potential loss of data).

If you choose to save it as a PNG, though, then you will lose no data relative to what you saw when you loaded it into Gimp (but of course data was lost in recording the image on your camera).

Whether, in practice, rotating a jpeg has a significant impact on its jpeg compressibility (i.e. whether jpeg compression is invariant with respect to 90 degree rotations) is a mathematical question about the quality of the jpeg agorithm, which I unfortunately don't know the answer to. But in practice, I have never observed noticeable degradation from doing this.

I still like to use PNG format images for intermediate work in Gimp (so long as I have the disk space, which has not been a problem so far), just to be safe. But it's more like a compulsive habit than a really documented need.

Cheers, Terry

--
Terry Hancock ( hancock at anansispaceworks.com ) Anansi Spaceworks http://www.anansispaceworks.com

"Some things are too important to be taken seriously"