Re: [gthumb-list] Bug: EXIF orientation is broken after resize

[damien clochard <damien dalibo info>]

Le 29/01/2013 16:30, Dr. Michael J. Chudobiak a écrit :
> > > the orientation field makes sense only in the original image, when you
> > > create a new image it is better to reset it.
> >
> > Sorry again but I don't understand this logic. I don't see how resetting
> > the orientation after a resize operation is useful to anyone. These are
> > two different things. My understanding is that gthumb should keep this
> > orientation when user ask for a resize.
> >
> > Am I correct ?
>
> No. The orientation tag is taken into account when the image is loaded
> into memory.
>
> The resize happens on the image in memory.

Yes I am aware that the transformation are executed "in memory" and not
directly on disk :-) Anyway I don't see how this is related with the
issue I described.


> To save it with your original orientation tag, another step would be
> required to rotate the image and copy the original tag. There is no
> advantage to adding that degree of complexity (and slowness).

But most EXIF fields are left unmodified... If you're able to copy some
of the original EXIF tags, why not do it for the orientation as well ?
Just don't modify it in the first place...

All I'm asking is "why are you changing the EXIF fields ?" and you're
answer is "because if we don't, it will add complexity and slowness"...

I'm confused.

> The resulting image should look correct, of course. If it doesn't, there
> is a bug. But the orientation tag should be reset.

Says who ? Where is it written that "the orientation tag should be
reset"? Is this a secret rule among graphic sofwtare developpers ? ;-)

I'm kinda new to all this and I guess I don't have enough knowledge to
understand why the EXIF oratientation tag is so bad. So I was curious
about that and I decided to run some tests with ImageMagick, LibreOffice
Draw, The Gimp, feh and the good old eog

Among these 5 tools :

  * feh seems to removes every single EXIF field from the file. The feh
philosophy sounds like "No EXIF, No Pain" :D
  * ImageMagick, LibreOffice Draw and eog don't modify the EXIF
orientation tag
  * The Gimp prompts a pop-up window, saying : "do you want to keep the
EXIF information  or rotate the image ?" Which is probably the smartest
thing to do.

None of them will modify the tag without warning the user.