Re: image-dired does not rotate the original image

[Mathias Dahl <brakjoller@gmail.com>]

Thien-Thi Nguyen <ttn@gnuvola.org> writes:

>    As I mentioned earlier, jpegtran does lossless rotation, something
>    `convert' cannot do (or could not the last time I checked).
>
> does this limitation also exist w/ mogrify(1) (or alternatively gm(1)
> subcommand mogrify)?

I don't know. What I do know is that `convert' makes a lossy rotation
of JPEGs. I found this out myself while creating Tumme; while in the
thumbnail buffer, rotate a thumbnail over and over again. Because of
the small size you soon begin to see changes.

>  cp foo.jpg foo.orig.jpg
>  gm mogrify -rotate -90 foo.jpg
>  gm mogrify -rotate  90 foo.jpg
>  cmp foo.jpg foo.orig.jpg
>
> however, doing the above (even w/ "-quality 100" for the mogrify commands)
> always results in cmp(1) noting a difference, even though visually i could
> not tell.

If you do that in a loop, say ten or more times, maybe you will start
to see a difference (save the original and compare it visually).

>  i'm not a graphics format expert; could you suggest a better
> way to check for loss?

How about rotating the image in Gimp, for comparison?

Maybe there should be an option in `image-dired' to allow lossy
rotation, so that people who accept that do not need to have
`jpegtran'?

/Mathias