Before using the denoiser you must download the plugin:

1. In the main menus, click Render ▸ Download NVIDIA OptiX Denoiser.

2. Restart Houdini.

For studio-wide installation, see manual installation below.

Turn on the Denoise button in the toolbar at the top of the render view. (This button is disabled if the plugin is not installed.)

In the Render View, the denoiser always uses the "basecolor" image plane (if it exists) as the albedo input.

In the parameter editor for the Mantra render node, click the Images tab, then click the Output sub-tab. Click the drop-down menu button next to the Pixel filter field and choose "NVIDIA OptiX Denoiser" (sets the field to denoise optix).

In the Pixel filter field you can optionally specify an image plane to use as the albedo input to the denoiser with the -a option, for example:

denoise optix -a mydiffuse

If you have more than one GPU in your computer, you can specify which one to use for denoising.

1. Run the following in command-line to see OptiX-capable devices listed in order:

   > hgpuinfo -o
   

2. Set the $HOUDINI_NVIDIA_OPTIX_DEVICENUMBER environment variable to the desired device ID, starting from 0 (for example, 0 to use the first device, 1 to use the second device).