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When no color manager is present an additional color space is used to allow for log LUT usage. Built-in color spaces are sRGB, linear, and cineon_log

The default OCIO color manager points at the default OCIO config.

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MultiExcerptNameBuilt-in Color Manager

Arnold has a built-in color manager. It implements the open-source OpenColorIO (OCIO) color management system and uses an OCIO v2 config shipped with Arnold. The color manager is configured to leverage the industry standard ACES color encoding system, setting the rendering color space to ACEScg. If no color manager is linked to in options.color_manager, the built-in one will take over.

This built-in color manager only knows about two color spaces:

  • 'sRGB' which corresponds to the sRGB colorspace with its corresponding gamma.
  • 'linear' which corresponds to a linear color space with the sRGB gamut and white point. This "sRGB linear" color space was the default rendering color space in Arnold 4.
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hiddentrue
MultiExcerptNamecineon_log
Note
Info

The name of the default OCIO color manager node is called ai_default_color_manager_ocio.


OCIO Color Manager

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MultiExcerptNameOCIO Color Manager

Through the 'color_manager_ocio' node Arnold can access color spaces defined in an OCIO config file.

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MultiExcerptNamecolor_space_linear

This is the default linear color space that Arnold will use as its rendering color space. Arnold's default color space is 'sRGB linear, ' but this can correspond to any linear color space if needed. If chromaticities for this linear color space can be guessed or are user-specified certain spectral effects will take them into account, but not no other adaptations for albedos, transparencies, etc. are applied.

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MultiExcerptNamelinear_chromaticities

The specific RGB and white point chromaticities of the rendering color space can be specified manually here. Arnold can also try to guess them if the reference 'sRGB gamma' color space is set in 'color_space_narrow'. 

View (Display) enumeration 

It's possible to enumerate all the view/display combinations available by specifying the "View (Display)" family when enumerating color spaces. This lets client programs filter color spaces when only a display transform is appropriate. For instance, in python you can get a list of available view/display combinations like this:

 

   total_spaces = AiColorManagerGetNumColorSpaces(cm)
view_displays = AiColorManagerGetNumColorSpaces(cm, "View (Display)")
for cs in range(0, view_displays) :
cn = AiColorManagerGetColorSpaceNameByIndex(cm, cs, "View (Display)")

 

Role enumeration 

It's possible to enumerate all the roles available in the current config by specifying the "Role (OCIO)" family when enumerating color spaces. This lets client programs filter color spaces when only roles are needed. In python you can get a list of available roles like this: 

   total_spaces = AiColorManagerGetNumColorSpaces(cm)
view_displays = AiColorManagerGetNumColorSpaces(cm, "Role (OCIO)")
for cs in range(0, roles) :
cn = AiColorManagerGetColorSpaceNameByIndex(cm, cs, "Role (OCIO)")

OCIO defaults

If certain roles are defined in the config, they will be used for the required color spaces, if node parameters do not override them. These roles are:

  • For linear color space (the rendering color space): rendering role, and if not present scene_linear or linear roles
  • For "narrow" bit width color space (the color space that will be used as sRGB, see above): srgb_equivalent role. If this role is not present a suitable equivalent will be chosen based on the current config's path and the available color space names.


If no chromaticities for the linear color space are supplied, a suitable default will be chosen based on the path to the current config and the name of the rendering color space. This enables the more accurate rendering of effects that generate very saturated colors (thin film, dispersion, physical sky, blackbody radiation)


All color spaces and chromaticities used by default will be reported in the render log and can be overridden as needed by setting the corresponding node parameters.



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