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Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB
From: |
Elle Stone |
Subject: |
Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB |
Date: |
Sun, 22 Feb 2015 09:03:07 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 |
On 02/21/2015 02:26 PM, Joseph Goldstone wrote:
The ACES committee (an unfortunate change of name from the Image
Interchange Framework committee) agreed with Florian on much of what was
published in this document, but let go of indirect output referred
imagery or output referred imagery in OpenEXR, IDCES and ODCES as
explicitly named things, and a lot of other stuff. For example, the ACES
1.0 release carries a lot of the metadata as clip-level XML that the
paper you reference proposes be carried as OpenEXR attributes
The ACES 1.0 source and doc bundle can be reached from this page:
http://www.oscars.org/science-technology/sci-tech-projects/aces
And if you are going to be looking at how to make OpenEXR files for an
ACES workflow, look at SMPTE ST 2065-4:2013, “ACES Image Container File
Layout”.
On 02/21/2015 07:10 PM, Gonzalo Garramuno wrote:
This is handled by the ACESclip metadata and CTL. It allows you to
have different Look Mod Transforms and save them along your image.
Or a gradeRef to convert from and to a different space (like log)
and apply ASC CDL transforms (SOPNode and SatNode).
mrViewer supports the first variety and is in progress to support
the second variety, too.
Thanks! for the links and the clarification on how ACES is used with
OpenEXR files. I've been peeping over my shoulder at the ACES workflow
and how people in the world of cinema handle color management for a
while now.
The context of my question about the OpenEXR document on ACES wasn't
about ACES per se but rather about how to use OpenEXR in a strictly
photographic workflow, as a way to transport high bit depth RGB data
between various photographic image editors that use ICC profile color
management (the ACES-OpenEXR propsal mentions encoding nonlinear RGB data).
The specific question was whether photographic image editors should
allow writing nonlinearly encoded RGB data to OpenEXR files, or whether
instead the RGB data should be converted to a linear gamma ICC profile
before being exported as OpenEXR.
In the usual photographic workflow, editing operations are performed
directly on the RGB data to intentionally modify the scene-linear nature
of the raw data that was captured by the camera. From the photographer's
point of view, whether data should be exported as linear or nonlinear
RGB depends on why the photographer wants to export the data. For
example, if the goal is to rescale the image in another image editor,
the data should be converted to a linear gamma ICC profile. But if the
goal is adding or removing noise, usually the photographer will prefer
results of operating on perceptually uniform data.
The question of writing nonlinearly encoded RGB values as OpenEXR came
up because the GIMP devs are currently working on GIMP's OpenEXR
read/write code. We (I contribute to GIMP development, mostly in the
area of ICC profile color management) want to accomodate the needs of
photographers while making sure we follow OpenEXR specifications and
best practices.
On 02/21/2015 02:26 PM, Joseph Goldstone wrote:>
The Academy doc set is in the unfortunate position of trying to provide
color-managed substrate around which digital motion picture workflows
could be built, while trying to stay agnostic with regards to workflow
and not provide a ‘best practice’ there. I’m not any sort of official
spokesperson for the Academy (just an 11-years-on-the-committee worker
bee) but I think they will stay agnostic, and see what kinds of
workflows are developed by productions and by interested individuals. My
guess is that over the next year the ACES discussion group at
https://groups.google.com/forum/?hl=en#!forum/academyaces
<https://groups.google.com/forum/?hl=en#%21forum/academyaces>
will move a bit from developer conversations to user conversations. And
I hope that, supplanting that discussion group which is pretty linear
and textual, we’ll see ACES usage discussions on websites like your own
(which I wish had been there in the early 2000s when I was trying to use
littlecms for movie production).
Does anyone use ACES in conjunction with ICC profile color management?
If so, do they use OpenEXR to store RGB data?
I wish OpenEXR supported ICC profile color management by means of
embedded ICC profiles.
If the data is converted to a linear gamma ICC profile before export as
OpenEXR, then the chromaticities and white point can be used to
construct an ICC profile. But many applications that do read ICC
profiles, don't read or write OpenEXR chromaticities plus white point
and don't have code that constructs ICC profiles from chromaticities
plus white point.
Elle
- [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Elle Stone, 2015/02/20
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Christopher Horvath, 2015/02/20
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Joseph Goldstone, 2015/02/21
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB,
Elle Stone <=
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Deke Kincaid, 2015/02/22
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Gonzalo Garramuno, 2015/02/22
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Deke Kincaid, 2015/02/22
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Haarm-Pieter Duiker, 2015/02/22
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Elle Stone, 2015/02/22
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Lars Borg, 2015/02/22
- Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Karl Rasche, 2015/02/22
Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB, Piotr Stanczyk, 2015/02/20