Re: [Openexr-devel] Colour space

[Kenneth A Lloyd]

First, I'd like to thank all for the great discussion.

 

There are many uses of color information.  It seems that most of the discussion in this forum centers on conversion and representation of color in photographic / CG representations in the entertainment and artistic domain.  There are other domains that rely on color information, both naturally and artificially embedded, including scientific and medical applications.  I suppose it would be helpful to determine a practical domain scope for using OpenEXR - sort of a sanctioned use-case scenario set .  How broadly or narrowly focused this scope is defined will allow others to determine what strategy they use in deciding about adopting or extending the OpenEXR standard, including dealing with implications for the meanings associated with spectrum, magnitude, error, non-linearity or application sensitivity curves.

 

It is unrealistic to try an make OpenEXR all things to all people, but to describe an intended domain range might help focus upon answers.

 

----------------------------------------------

Ken Lloyd

Sr. Software Architect

Watt Systems Technologies

 

 

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From: address@hidden [mailto:address@hidden On Behalf Of gary demos
Sent: Monday, September 06, 2004 10:54 AM
To: darrel j butlin
Cc: address@hidden
Subject: Re: [Openexr-devel] Colour space

Darrel,

Good question about RIMM.  Of course, RIMM is input referenced (as ROMM is output referenced).   Further,
 RIMM has extended range, both dynamically and in color gamut.   It uses red, green, and blue primaries which
 are non-physical, at a little beyond the spectrum locus, getting nearly all pure colors except for a little bit in
 the pure cyan area.

The ERIMM is the most interesting to me, since it is logarithmic.

The problem with RIMM and ROMM, as well as with XYZ and most other systems (e.g. Rec 709 HDTV) is
 that the color primaries are specified in terms of CIE 1931 xy chromaticity coordinates.  This is also true for
 the primaries in the OpenExr header.

CIE 1931 xy chromaticity relies upon x_bar, y_bar, and z_bar spectral matching functions, which are known to
 have some errors in certain color regions (especially near cyan at 500nm, but also at other places in the spectrum).
 I have been inquiring of color scientists concerning a) how much of a problem are the errors in CIE 1931 XYZ,
 and b) how much benefit is there from going to more than three color primaries for the device-independent space.

I am speaking personally, and not in any official capacity, and certainly not as anything more than a user of OpenExr.

-Gary Demos


darrel j butlin wrote:

Hi,

I would just like to enquire whether anyone can clarify that the ideal colour space for openeXR image files is RIMM.

Presumably, the XYZ colour space is not supported in the cinematic industry and therefore, images written in XYZ would cause colour management complications during the postproduction and recording process…. can anyone comment on this?

Darrel J Butlin

www.darrel.info

Tel: 0117 9744925

Mob: 079 29288815

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