Download and Installation

Arnold, KtoA, and other downloads are available here. Installation instructions come with KtoA, but can also be viewed here: Installation.


  • Arnold: 5.2.0+
  • Katana: 2.6v4+, 3.0v1+
  • Platforms:
    • Linux: x86-64, RHEL 6+ or compatible glibc
    • Windows: 7+ on x86-64, with VC++ 2015 redistributable installed


  • Update to Arnold 5.2: Arnold comes bundled. See the release notes for more information. The highlights are below. (#317)

    • New shaders: matrix_multiply_vector and matrix_transform shaders have been brought back from the old common shaders, and a flexible cell_noise shader has been added.

    • Sheen BRDF: standard_surface now has a sheen layer just above diffuse and subsurface scattering, simulating materials such as velvet.

    • Texture baking: a new uv_camera has been added to assist in baking out textures. To accommodate extending borders to the edge of the output texture, rendering with this type of camera is only supported for disk renders, and only with tiling turned off for outputs (on ArnoldOutputChannelDefine).

    • Performance improvements: adaptive subdivision is faster and now fully multithreaded, and EXR read performance has improved.

    • Spherical light sampling: spherical light sampling (point lights with non-zero radius) has improved, showing sometimes significant reductions in noise especially at grazing angles as is common in rim lighting.

    • Denoising improvements:  noice has improved in stability and flexibility of image properties, and the OptiX-based denoiser uses less memory and has fewer fringing artifacts for HDR renders.

    • More volumetric AOVs: volumes now output volume_Z and ID AOVs, allowing selection of volumes in the monitor.

    • Cryptomatte: Cryptomatte now ships with Arnold and KtoA, and is available by default.

    • Toon ID:  ArnoldObjectSettings now has a toon_id parameter, where if this is set on multiple locations they will not have an outline drawn between them, but will act as if they are the same object for toon outline purposes. Note that you can also set string toon_id arbitrary data with ArnoldUserData directly, even for just some faces on an object, to drive outlines within objects as well. (#317)
    • Denoiser node:  ArnoldDenoise has been added which supports both interactive (preview/live) renders with the OptiX denoiser, and disk renders with noice. It only supports single-frame denoising, and each dedicated AOV/output to be denoised will be denoised separately, but even so it vastly simplifies the workflow for setting up denoising in KtoA. (#318, #289)

Incompatible Changes

  • Automatic type inference for arbitrary data: Introduced in version 2.0.7 was automatic type inference where float data of stride 3, 4, 9 or 16 would automatically be interpreted as Arnold type VECTOR, RGBA and MATRIX (for both 9 and 16 cases). This causes problems when this was not intended, and the hack attribute geometry.arbitrary.<name>.strictType was added for force KtoA to skip this automatic type inference. Given that the arbitrary data should be formed correctly in the first place, and then have either geometry.arbitrary.<name>.inputType or geometry.arbitrary.<name>.outputType set to indicate a particular interpretation, the automatic type deduction is removed. Please set the arbitrary data attributes properly to tell KtoA how to interpret your user data. (#312)

  • Simplified Arnold plugin directories layout: KtoA now loads Arnold plugins automatically only from the RenderPlugins directory in the KtoA root, and the old shaders, volumes and procedurals directories are no longer searched even if present. Arnold will continue to attempt loading plugins from the plugins directory, however. Users are encouraged to bundle their plugins and point to them using the ARNOLD_PLUGIN_PATH environment variable. (#317)

  • Renamed and removed parameters: The GPU-related parameters in ArnoldGlobalSettings have been renamed to use a gpu_ prefix. The texture_<type>_blur settings have been removed, as they are no longer needed and are usually detrimental. Use the Arnold update shelf script to clean up these parameters. (#317)


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