Re: [Openexr-devel] EXIF meta data attributes in headers

[Peter Hillman]

What extra info do you get from the ICC profile?

Allowing ICC profiles worries me. Aren't EXRs supposed to store pixel 
values in "input scene referred linear-light" encoded with the 
chromaticities specified? That means images must be linearised before 
storing in an EXR.

As I understand the ICC workflow (which admittedly is only very 
slightly), the profile encodes the mapping between the stored pixel 
values and the input or output response. That implies the image encoding 
can be something other than "input scene referred linear light".
If you start allowing ICC profiles in EXRs, you get ambiguity about how 
the data is meant to be interpreted. Even if the ICC profile was meant 
to be purely informational, so you know how the original camera encoded 
the data, there's still a danger that some helpful package will offer to 
interpret the transform in the profile and encode the data, or offer the 
ability to write sRGB encoded EXRs with an ICC profile, and then 
suddenly the EXR standard gets broken.

Ambiguity in metadata is annoying but tolerable; ambiguity in how to 
read or write the image is far more worrying.

If there's other useful info in the ICC profile, then lets extract it 
and store it in new standard attributes.



On 19/07/13 11:13, Brendan Bolles wrote:
> On Jul 18, 2013, at 3:08 PM, Larry Gritz wrote:
>
> > If you think any of these are supposed to represent the same data, you can get 
> > into problems when an app reads the EXR file, just copies XMP to output, but 
> > changes one of the related OpenEXR fields. Then you end up with an output file 
> > that has metadata that in some sense contradicts itself.
>
> In most cases I imagine they'll only have one form of metadata coming in and 
> any other EXR attributes they add will be parsed from that source.
>
> For example, I currently get ICC profiles from the Adobe apps, which I then 
> parse out to make Chromaticity attributes.  But an ICC profile can have 
> information that can't be reconstructed from chromaticities, so that's why I 
> embed the whole thing as well.
>
> Anyway, let's not let perfect become the enemy of good.  The benefit of getting 
> more metadata outweighs the risk of getting conflicting metadata, which I would 
> call a bug for the app developer.
>
>
> Brendan
> _______________________________________________
> Openexr-devel mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/openexr-devel