OpenColorIO

Open Source Color Management

OpenColorIO v1.0.8 documentation

Tool overview

OCIO is comprised of many parts. At the lowest level there is the C++ API. This API can be used in applications and plugins

Note that all these plugins use the same config file to define color spaces, roles and so on. For information on setting up configurations, see Configurations

The API

Most users will never directly interact with the C++ API. However the API is used by all the supplied applications (e.g ocio2icc) and plugins (e.g the Nuke plugins)

To get started with the API, see the Developer guide

ociocheck

This is a command line tool which shows an overview of an OCIO config file, and check for obvious errors

For example, the following shows the output of a config with a typo - the colorspace used for compositing_log is not incorrect:

$ ociocheck --iconfig example.ocio

OpenColorIO Library Version: 0.8.3
OpenColorIO Library VersionHex: 525056
Loading example.ocio

** General **
Search Path: luts
Working Dir: /tmp

Default Display: sRGB
Default View: Film

** Roles **
ncf (default)
lnf (scene_linear)
NOT DEFINED (compositing_log)

** ColorSpaces **
lnf
lgf
ncf
srgb8 -- output only

ERROR: Config failed sanitycheck. The role 'compositing_log' refers to a colorspace, 'lgff', which is not defined.

Tests complete.

It cannot verify the defined color transforms are “correct”, only that the config file can be loaded by OCIO without error. Some of the problems it will detect are:

  • Duplicate colorspace names
  • References to undefined colorspaces
  • Required roles being undefined
  • At least one display device is defined

As with all the OCIO command line tools, you can use the –help argument to read a description and see the other arguments accepted:

$ ociocheck --help
ociocheck -- validate an OpenColorIO configuration

usage:  ociocheck [options]

    --help        Print help message
    --iconfig %s  Input .ocio configuration file (default: $OCIO)
    --oconfig %s  Output .ocio file

ociobakelut

A command line tool which bakes a color transform into various color lookup file formats (“a LUT”)

This is intended for applications that have not directly integrated OCIO, but can load LUT files

If we want to create a lnf to srgb8 viewer LUT for Houdini’s MPlay:

$ ociobakelut --inputspace scene_linear --shaperspace lg10 --outputspace srgb8 --format houdini houdini__lnf_to_lg10_to_srgb8.lut

The --inputspace and -outputspace options specify the colorspace of the input image, and the displayed image.

Since a 3D LUT can only practically operate on 0-1 (e.g a Log image), the --shaperspace option is specified. This uses the Houdini LUT’s 1D “pretransform” LUT to do “lnf” to “lg10”, then the 3D LUT part to go from “lg10” to “srgb8” (basically creating a single file containing a 1D linear-to-log LUT, and a 3D log-to-sRGB LUT)

To make a log to sRGB LUT for Flame, the usage is similar, except the shaperspace option is omitted, as the input colorspace does not have values outside 0.0-1.0 (being a Log space):

$ ociobakelut --inputspace lg10 --outputspace srgb8 --format flame flame__lg10_to_srgb.3dl

See the What LUT Formats are supported? section for a list of formats that support baking

ocio2icc

A command line tool to generate an ICC “proofing” profile from a color space transform, which can be used in applications such as Photoshop.

A common workflow is for matte-painters to work on sRGB files in Photoshop. An ICC profile is used to view the work with the same film emulation transform as used in other departments.

ocioconvert

Loads an image, applies a color transform, and saves it to a new file.

OpenImageIO is used to open and save the file, so a wide range of formats are supported.

ociodisplay

A basic image viewer. Uses OpenImageIO to load images, and displays them using OCIO and typical viewer controls (scene-linear exposure control and a post-display gamma control)

May be useful to users to quickly check colorspace configuration, but primarily a demonstration of the OCIO API

Nuke plugins

A set of OCIO nodes for The Foundry’s Nuke, including:

  • OCIOColorSpace, transforms between two color spaces (similar to the built-in “ColorSpace” node, but the colorspaces are described in the OCIO config file)
  • OCIODisplay to be used as viewer processes
  • OCIOFileTransform loads a transform from a file (e.g a 1D or 3D LUT), and applies it
  • OCIOCDLTransform applies CDL-compliant grades, and includes utilities to create/load ASC CDL files