Config syntax

OpenColorIO is primarily controlled by a central configuration file, usually named config.ocio. This page will only describe how to syntactically write this OCIO config - e.g. what transforms are available, or what sections are optional.

This page alone will not help you to write a useful config file! See the Configurations section for examples of complete, practical configs, and discussion of how they fit within a facilities workflow.

YAML basics

This config file is a YAML document, so it is important to have some basic knowledge of this format.

The Wikipedia article on YAML has a good overview.

OCIO configs typically use a small subset of YAML, so looking at existing configs is probably the quickest way to familiarise yourself (just remember the indentation is important!)

Checking for errors

Use the ociocheck command line tool to validate your config. It will inform you of YAML-syntax errors, but more importantly it performs various OCIO-specific validations. There are also validate methods on the Config class in the C++ and Python APIs, (although they do not do the role checking that ociocheck does).

For more information, see the overview of ociocheck

Config sections

An OCIO config has the following sections:

  • Config header – The header contains the version and LUT search path.

  • Environment – The environment defines the context variables used in the config.

  • Roles – The roles define which color spaces should be used for common tasks.

  • File & Viewing rules – These rules define sensible defaults that help applications provide a better user experience.

  • Displays & Views – This section defines how color spaces should be viewed.

  • Looks – Looks are transforms used to adjust colors, such as to apply a creative effect.

  • Colorspaces – This section defines the universe of color space encodings available within the config.

A collection of Available transforms is provided for use in the various sections of the config file.

Config header

ocio_profile_version

Required.

By convention, the profile starts with ocio_profile_version.

This is a string, specifying which version of the OCIO config syntax is used.

The currently supported version strings are 1 and 2.

ocio_profile_version: 2

description

Optional. A brief description of the configuration.

search_path

Optional. Default is an empty search path.

search_path is a colon-separated list of directories. Each directory is checked in order to locate a file (e.g. a LUT).

This works is very similar to how the UNIX $PATH env-var works for executables.

A common directory structure for a config is:

config.ocio
luts/
  lg10_to_lnf.spi1d
  lg10_to_p3.3dl

For this, we would set search_path as follows:

search_path: "luts"

In a color space definition, we might have a FileTransform which refers to the LUT lg10_to_lnf.spi1d. It will look in the luts directory, relative to the config.ocio file’s location.

Paths can be relative (to the directory containing config.ocio), or absolute (e.g. /mnt/path/to/my/luts)

Multiple paths can be specified, including a mix of relative and absolute paths. Each path is separated with a colon :

search_path: "/mnt/path/to/my/luts:luts"

Paths may also be written on separate lines (this is more Windows friendly):

search_path:
  - luts1
  - luts2

Finally, paths can reference OCIO’s context variables:

search_path: "/shots/show/$SHOT/cc/data:luts"

This allows for some clever setups, for example per-shot LUT’s with fallbacks to a default. For more information, see the examples in Looks Example

family_separator

Optional. Defines the character used to split color space family strings into hierarchical menus. It may only be a single character. If no separator is defined, the Menu Helpers API will not generate hierarchical menus.

family_separator: /

inactive_colorspaces

Optional. Identify a list of color spaces that should not be used. These spaces may stay in the config and will still work in ColorSpaceTransforms, but they will not be added to application menus. This will be overridden by the environment variable OCIO_INACTIVE_COLORSPACES.

inactive_colorspaces: [ do_not_use_this_colorspace, prev_version_colorspace ]

luma

Deprecated. Optional. Default is the Rec.709 primaries specified by the ASC:

luma: [0.2126, 0.7152, 0.0722]

These are the luminance coefficients, which can be used by OCIO-supporting applications when adjusting saturation (e.g. in an image-viewer when displaying a single channel)

Note

While the API method is not yet officially deprecated, luma is a legacy option from Imageworks’ internal, closed-source predecessor to OCIO.

The luma value is not respected anywhere within the OCIO library. Also very few (if any) applications supporting OCIO will respect the value either.

Environment

environment

Optional. The envrionment section declares all of the context variables used in the configuration.

environment:
  SEQ: default_sequence
  SHOT: $SHOT

It is highly recommended that config authors using context variables include the environment section for the following reasons:

  • It provides performance benefits to applications

  • It will make the config easier to read and maintain

  • It allows defining default values

  • It improves the validation that may be performed on a config

This config uses two context variables: SEQ and SHOT. SEQ has a default value of default_sequence. This is the value that will be used if the environment does not contain the SEQ variable and the context variable is not otherwise defined. The SHOT variable does not have a default and hence the use of the syntax shown.

The environment must be self-contained and may not refer to any other variables. For instance, in the example above it would not be legal to have SHOT: $FOO since FOO is not one of the declared variables.

Every context variable used in the config must be declared since no other environment variables will be loaded into the context. In studios that use a large number of environment variables, this may provide a performance benefit for applications.

Roles

roles

Required.

A “role” is an alias to a color space, which can be used by applications to perform task-specific color transforms without requiring the user to select a color space by name.

For example, the Nuke node OCIOLogConvert: instead of requiring the user to select the appropriate log color space, the node performs a transform between scene_linear and compositing_log, and the OCIO config specifies the project-appropriate color spaces. This simplifies life for artists, as they don’t have to remember which is the correct log color space for the current project - the OCIOLogConvert always does the correct thing.

A typical role definition looks like this, taken from the spi-vfx example configuration:

roles:
  color_picking: cpf
  color_timing: lg10
  compositing_log: lgf
  data: ncf
  default: ncf
  matte_paint: vd8
  reference: lnf
  scene_linear: lnf
  texture_paint: dt16

All values in this example (such as cpf, lg10 and ncf) refer to color spaces defined later the config, in the colorspaces section.

Here is a description of the roles defined within OpenColorIO. Note that application developers may also define roles for config authors to use to control other types of tasks not listed below.

Warning

Unfortunately there is a fair amount of variation in how applications interpret OCIO roles. This section should be expanded to try and clarify the intended usage.

  • aces_interchange - defines the color space in the config that implements the ACES2065-1 color space defined in SMPTE ST2065-1. This role is used to convert scene-referred color spaces between different configs that both define this role.

  • cie_xyz_d65_interchange - defines the color space in the config that implements standard CIE XYZ colorimetry, adapted to a D65 white. This role is used to convert display-referred color spaces between different configs that both define this role.

  • color_picking - colors in a color-selection UI can be displayed in this space, while selecting colors in a different working space (e.g. scene_linear or texture_paint)

  • color_timing - color space used for applying color corrections, e.g. user-specified grade within an image viewer (if the application uses the DisplayTransform::setDisplayCC API method)

  • compositing_log - a log color space used for certain processing operations (plate resizing, pulling keys, degrain, etc). Used by the OCIOLogConvert Nuke node

  • data - used when writing data outputs such as normals, depth data, and other “non color” data. The color space in this role should typically have data: true specified, so no color transforms are applied

  • default - when strictparsing: false, this color space is used as a fallback. If not defined, the scene_linear role is used

  • matte_paint - color space which matte-paintings are created in (for more information, see the guide on baking ICC profiles for Photoshop, and spi-vfx)

  • reference - the color space against which the other color spaces are defined

Note

The reference role has sometimes been misinterpreted as being the space in which “reference art” is stored in.

  • scene_linear - the scene-referred linear-to-light color space, often the same as the reference space (see:ref:faq-terminology)

  • texture_paint - similar to matte_paint but for painting textures for 3D objects (see the description of texture painting in SPI’s pipeline)