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

[Elle Stone]

On 02/22/2015 09:32 AM, Deke Kincaid wrote:
> Hi Eli
>
> I would look at a project called OpenColorIO (OCIO).  It is a common way
> many DCC applications handle color these days via luts, cdl and a
> variety of other color transforms.  Through OCIO you could transform to
> scene linear, apply a viewer transform and have the appearance of
> working in some type of display referred space.  It also includes a tool
> to bake icc files which is how the ACES profile for Photoshop was created.
>
> http://opencolorio.org/
> http://opencolorio.org/userguide/baking_luts.html?highlight=icc
> https://github.com/imageworks/OpenColorIO
>
> There are ACES config files for ocio too
> https://github.com/imageworks/OpenColorIO-Configs

Hi Deke,

Right now GIMP only uses ICC profile color management and only works 
with display-referred "print-oriented" (electronic or paper) images. At 
some point in the future I'm pretty sure the plan is to accomodate HDR 
scene-referred editing, at which point implementing OCIO would be a 
really good thing to do.

Even when that happy day arrives, many GIMP users will still want to use 
ICC profile color management. And other ICC profile color managed 
editing applications with which GIMP users might want to exchange high 
bit depth OpenEXR images, might not support OCIO.

In the meantime, if you don't mind some (possibly really dumb) questions 
from someone who doesn't know anything at all about OCIO:

1. Can you configure OCIO to use information that in an ICC profile 
workflow is contained in the monitor's ICC profile? So that what is seen 
on the screen in an OCIO workflow looks like what you'd see in an ICC 
profile color-managed workflow? For example, my LCD monitor is not (and 
can't be) calibrated to exactly match sRGB. Rather it's profiled in its 
native state for maximum color gamut and smoothest tonal transitions.

2. Is there information on the web that explains OCIO color management 
to people like myself who've only ever used ICC profile color management?

3. In a strictly output-referred workflow - digital paintings or 
photographic editing of images that will be displayed as a paper print 
or on a display device - what advantage would there be in adapting 
OCIO/ACES rather than using an ICC profile color managed workflow?

To put some context around this third question, many algorithms have 
been written to make photographic images "instantly pretty" and surely 
these algorithms can be encoded "via luts, cdl and a variety of other 
color transforms".

However, some photographers don't use automated tools to achieve 
"instant pretty". Rather they analyze the image and process it "part by 
part", as per the wet darkroom, where a flat print is made and then 
examined to determine where to apply dodging and burning to make the 
final print match the photographer's envisioned rendering.

This latter approach involves using masks and layers to confine various 
processing steps to specific parts of the image. I'm not very clear on 
how/where this hands-on "masks and layers" approach to photographic 
image editing can be accomodated in an OCIO/ACES workflow.

Elle