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This page provides information about the proper ACEScg color space workflow with V-Ray 5 for Houdini.

Overview

ACES is the Academy Color Encoding System and developed by the Academy of Motion Picture Arts and Sciences. ACEScg is the version of the ACES encoding system for computer graphics, widely adopted in the industry. It has become the industry standard, because compared to sRGB, ACEScg works with a lot more color information, illustrated in this gamut graph.

V-Ray 5 comes with an implementation of the ACEScg out of the box and in this tutorial we explain the rendering setup in V-Ray for Houdini in this color space. There are two ways of setting up ACEScg for rendering and display: manually and using an OCIO configuration.

 

V-Ray supports only ACEScg as the primary color space of choice in CGI and not other ACES color spaces such as ACEScc or ACEScct.

 

 

Manual Setup

You need to specify ACEScg as the rendering color space in Houdini.

Go to Renderer node > Renderer > Color Mapping  and set the RGB Color Space to ACEScg.

In all cases, in addition to bitmaps, V-Ray converts the light’s temperature settings, the V-Ray Sun & Sky, the V-Ray Temperature texture and the V-Ray Material dispersion to the rendering color space.

 

 

 

If you have some files that are exceptions to the rule-based system, you can override the color space of a specific file node from its parameters.

For example, in the Image File texture, go to Bitmap tab > RGB Primaries and select the color space, in which the texture is encoded.

 

 

 

The new Frame Buffer in V-Ray 5 provides a filmic tonemap correction in AMPAS mode that emulates the OCIO display transformation, which can be used instead of an OCIO configuration.

 

 

OCIO configuration

An automated OCIO configuration can be set with the OCIO environment variable.
 

There are few steps you need to follow to set this up:

 

  1. Download the Open Color IO configuration package from GitHub: https://github.com/colour-science/OpenColorIO-Configs

  2. Set the OCIO environment variable and point it to the config.ocio file.
    For example, to set up the OCIO configuration with aces_1.2:

    Windows: set OCIO=C:\OpenColorIO-Configs\aces_1.2\config.ocio
Linux: export OCIO=/home/user/OpenColorIO-Configs/aces_1.2/config.ocio
macOS: export OCIO=/home/user/OpenColorIO-Configs/aces_1.2/config.ocio

    The existence of this environment variable controls whether Houdini automatically uses OCIO in various places.


  3. You can then use the OCIO Input Color Space Rules or define custom rules within Houdini.

 

 

 

4. When the VFB Display Correction is switched to OCIO, V-Ray reads the OCIO variable and loads the configuration there as well. Choose ACES - ACEScg for your Input Colorspace and sRGB for your View Transform. Leave the Display Device at ACES.

 

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