Re: Endless gamma in eXIf 2017-0119

I verified that ImageMagick doesn't modify the Exif profile when
it changes the image data

convert sony_dsc_h1.jpg -gamma 3 sony_dsc_h1_gamma3.jpg
convert sony_dsc_h1.jpg sony_dsc_h1.exif
convert sony_dsc_h1_gamma3.jpg sony_dsc_h1_gamma3.exif
cmp *.exif

The two .exif files are identical, but one image is much darker
than the other.

So this may be bad behavior, but it has nothing to do with PNG or
eXIf/eXIF chunks.  The PNG encoder, when writing an eXIF
chunk, will do what it's told to do, namely to write an unmodified
Exif profile.  The presence of the profile in the JPEG image
being decoded seems to have no effect on the decoding.

This testing with ImageMagick version 6.8.9-9 which is
about two years out of date.

Glenn

On Mon, Feb 6, 2017 at 8:44 PM, Willem van Schaik <[email protected]> wrote:

>
> And also, if we would make the chunk "unsafe to copy" what does prevent
> an application developer to still copy the chunk? In the end, these are
> just "suggestions".
>
> We're still relying on both developers and users to act responsibly.
> Which is for me the right thing to do. They know what their applications
> are doing.
>
> Protection against hackers, I'm all for it, but protecting dumb users, I
> don't know why we should. :)
>
> Willem
>
>
>
>
>
> On 2017-02-06 19:33, John Bowler wrote:
> > As Soni L. observed:
> >
> >> Shouldn't eXIf be considered "sensor/camera data" and thus only useful
> for ppl who >know what they're doing, and not automatically mangled into
> the image?
> >
> > Yes; that's how I see it.  It's used to allow a digital camera image
> > to be expressed in PNG and the workflows which use it will be similar
> > to the ones which use EXIF in JPEG or TIFF.   Exactly the same problem
> > of maintaining it without updating it exists in JPEG and TIFF too, and
> > of course it already exists in the current zTXt encoding.
> >
>
> --
> Willem van Schaik
> [email protected]
>
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