The Arnold section in the Preferences window (Edit > Preferences...) contains global application level settings.

Arnold

Arnold in Main Manu Bar

When enabled, the Arnold plugin menu is added to the application menu bar as a separate entry.

When disabled, the Arnold plugin menu is under the Extensions menu.

Material

Default Material System

The default material system decides whether a Node Material or an old Arnold Material is created when creating an Arnold material from the plugin (e.g. Create > Arnold menu in the Material Manager, context menu in the IPR window, etc.).

Render Material Preview

When disabled, no Arnold material previews are rendered in the scene, either Arnold Material or Node Material.

Render Shader Previews

When disabled, no shader previews are rendered in an Arnold Node Material.

Viewport Preview

When disabled, Arnold materials are not displayed in the viewport, either Arnold Material or Node Material.

Light

Viewport Preview

When disabled, Arnold lights are not displayed in the viewport.

Textures

Tx Generation

Tx is a tiled and mipmapped texture format, which will dramatically improve time to the first pixel, overall render time, and memory usage. Therefore converting textures to Tx files is highly recommended.

You can choose your preferred workflow of generating Tx textures:

  • none: No Tx files are generated, the original textures are used. Note that this mode is recommended is special cases only because it can hurt performance.
  • manual: Use the Tx Manager to generate Tx files manually when needed (e.g.original texture has been modified, color space has been changed, etc.). Existing Tx files are used in the render instead of the original images.
  • auto: Textures are automatically converted to Tx files before rendering the scene. Textures are converted from the image color space to the render color space. Each 8-bit texture is converted to 16-bit float data type images to avoid quantization errors in dark tones
    This are the options passed to the maketx tool:
-u --unpremult --oiio (--colorconvert [image_space] [render_space] --colorconfig [config]) (--format exr -d half --compression dwaa)

Imager

Default LUT Folder

Select a folder which will be set as the LUT folder by default in a newly created tonemap imager.

Default LUT File

Select a LUT file which will be set by default in a newly created tonemap imager.

Default Color Manager

Enable

When enabled, the selected color manager will be set when a new scene is created or a new render settings is added to an existing scene.

Color Manager

Defines the color manager used in the scene.

default - ACES

The default color manager 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.

Find more information on the ACES workflow here.

legacy

This built-in color manager (the default color manager in Arnold 6) supports two color spaces:

  • 'sRGB' which corresponds to the sRGB colorspace with its corresponding gamma curve.
  • 'linear' which corresponds to a linear color space with the sRGB gamut and white point.

This color manager is equivalent to the native color management in Cinema 4D.

OCIO

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

Config

A path to the OCIO config file to use, if this is empty OCIO will try to load the config file from the 'OCIO' environment variable.

sRGB color space (narrow)

If it exists in the OCIO config, this should be set to the name of the 'sRGB Gamma' color space. This is used internally for input and output color spaces in 'auto' mode. If set by the user, this color space is also used as a reference to detect the rendering color space gamut and white point.

Linear sRGB color space

This is the default color space used on linear input textures which uses sRGB primaries. Typically HDR (high dynamic range) images, e.g. skydome or area light textures.

Render color 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 no other adaptations for albedos, transparencies, etc. are applied.

View Color Space

Viewer devices (e.g. monitor, TV screen, etc.) have limited dynamic range and color gamut. To display the rendered image properly on these devices, it has to be transformed to the viewing color space (usually Rec 709 for TV and sRGB for web).

Bake View Color Space Into Output

When rendering to the Picture Viewer or in Commandline or Team Viewer, Cinema 4D applies its native sRGB color transform, expecting the output to be in linear color space with sRGB primaries. That's not the case in Arnold when using a custom color manager (e.g. an ACES workflow with a custom view transform).

To get the correct output, this flag has to be set based on the image format we are targeting:

  • Turn on the flag when saving to an 8/16-bit integer image (e.g. JPEG, PNG, etc.).
  • Turn off the flag when saving to a 32-bit float image (e.g. EXR).

As opposed to the native workflow where you can save the rendered image from the Picture Viewer to any format, this flag must be set before rendering, defining the output format beforehand.

  • If the flag is turned on and saved to an EXR, the image will be incorrect, because Cinema 4D applies an sRGB -> linear transform, yet the image is in the View Color Space instead of sRGB.
  • If the flag is turned off and saved to a JPEG or PNG, the image will be incorrect, because Cinema 4D applies a linear -> sRGB transform, yet the image is in the Render Color Space (e.g. ACEScg) which is a wider gamut linear space.



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