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"
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