Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB

[Christopher Horvath]

I would strenuously argue this is correct for the R, G, & B channels, specifically:

Others have maintained that statements in the OpenEXR documentation such as "By convention, OpenEXR stores scene-referred linear values in the RGB floating-point numbers" (Technical Introduction to OpenEXR) should be interpreted to mean that OpenEXR RGB data should always be encoded as linear gamma data, and that reading and writing of non-linearly encoded RGB data shouldn't be supported.

Though I'm sure there are wildly differing uses.  There's no reason you couldn't create Rnonlinear, Gnonlinear, Bnonlinear channels or something similar, if you intend to break with convention.

C 

 

On Fri, Feb 20, 2015 at 12:45 PM, Elle Stone <address@hidden> wrote:

Hi all,

I'm involved with GIMP development as it pertains to ICC profile color management. GIMP is primarily used for processing photographic images and for creating digital art.

We are having a discussion about whether it's OK to read and write OpenEXR RGB files that aren't encoded using linear gamma RGB data.

Some of us have argued that:

* OpenEXR is a data container.
* Nothing in the OpenEXR specifications forbids reading or writing non-linearly encoded RGB data.
* After opening the file in an ICC profile color managed editing application, it should be up to the user to assign the correct ICC profile to interpret the data.

Others have maintained that statements in the OpenEXR documentation such as "By convention, OpenEXR stores scene-referred linear values in the RGB floating-point numbers" (Technical Introduction to OpenEXR) should be interpreted to mean that OpenEXR RGB data should always be encoded as linear gamma data, and that reading and writing of non-linearly encoded RGB data shouldn't be supported.

We were hoping you all could shed some light on this question.

Thanks in advance for advice as to whether there really is a requirement that OpenEXR RGB data always be encoded linearly.

Elle Stone
--
http://ninedegreesbelow.com
Color management and free/libre photography

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