[Openicc] Proof of concept, storing profile in X atoms

[Chris Murphy]

On Jun 17, 2005, at 8:42 AM, Ross Burton wrote:

> On Fri, 2005-06-17 at 08:25 -0600, Chris Murphy wrote:
>
>> The latest version of EXIF, I think it's 2.2, also allows for Adobe
>> RGB (1998).
>>
>
> I've got the 2.2 specification in front of me, and ColorSpace is  
> either
> 0x0001 (sRGB) or 0xFFFF (uncalibrated).  I'll have a hunt and see if
> there is a newer specification.

There is a 2.21 spec, but I can't figure out how Adobe RGB (1998)  
would be encoded. I know such images exist, direct from some digital  
cameras, and that this was tripping some people up on OS X where it  
wouldn't recognize they were Adobe RGB (1998) but Photoshop CS would.  
Maybe they're encoding gamma and primaries elsewhere, and setting the  
colorspace tag to uncalibrated.

I do wonder about the usefulness of EXIF colorspace data as it's  
currently employed. There are quite a few digital cameras that set  
the colorspace tag to sRGB yet they do not have sRGB behavior. And  
the camera claiming to convert its data into Adobe RGB (1998) did an  
impressively poor job of doing so.

It's been questionable enough that Adobe was compelled to release a  
plug-in to ignore the EXIF color space tag; and include a checkbox  
directly in application preferences in subsequent versions.


> Pretty much, yes.  Eye Of Gnome, the image viewer I've been working
> with, using libexif to expose the EXIF to the user so I can use the  
> data
> there to create a profile.  I need to find out how to get to the
> embedded ICC profile (if present) and try and find a way of wrapping
> this in a library.  One option is to move this functionality into  
> GTK+,
> the widget set for the GNOME desktop.

Anything that can be done to, prevent applications from stripping  
profiles from images, is a good thing. Naturally I'd like to see all  
applications actually use embedded profiles as source profiles, and  
embed profiles in all images that get saved. (Certain exceptions for  
CMYK, of course.) But the stripping of embedded ICC profiles, which  
is altogether too common when opening an image, rotating it or  
cropping it and resaving it, is absolutely unforgivable. It's data loss.

This has been overlooked on Mac OS and Windows for some time. It  
still happens on Windows all too often. On Mac OS, now there are APIs  
that developers are encouraged to use when handling images to avoid  
this problem. However, it does still happen. Perhaps it's too big of  
a problem to solve and people will simply need to be vigilant about  
what applications touch their images.


Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
-------------------------------------------------------------
Co-author "Real World Color Management, 2nd Edition"
Published by PeachPit Press (ISBN 0-321-26722-2)