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This node sets up various render settings needed to render holdout (also known as “matte”) objects, as well as to render with a background image.
(Behind the scenes, this node sets the Holdout Mode render setting on the matte objects to “background”, sets the matte objects for phantom shadow capture, and sets a render background image.)
Create the model(s) you want to be holdouts.
Create a Background Plate node in your LOP network.
After the Background Plate, add a Karma Render Properties node if your network doesn’t already have one.
In the Background Plate parameters:
Set the Primitives to a space separated list of prim paths of the objects you want to be hold-outs.
Set Plate to the file path of the background image to use. (You can use the Scale and Translate parameters to position the background image relative to the camera view.)
If you're using frame-by-frame background images in an animation, you can use a filename expression for the plate path, for example
Wire the Background Plate’s second output (which contains AOV settings) to the Karma Render Properties node’s second input (which accepts extra AOV settings).
On the Karma Render Properties node’s parameters, click the Image Output tab, then click the AOVs (Render Vars) sub-tab, then turn on Import Render Vars From Second Input.
By default, the node creates AOVs for diffuse bounces and light emissions on holdout objects. You can use these in compositing to better integrate the CG elements with the background.
Contains the USD stage, modified by this node. This is the standard output of a LOP node.
Output render vars
Contains the AOV (render var) settings specified in this node. If you are using the Karma node for rendering, you should connect this output to the Karma node’s second input to have them override the Karma node’s default settings.
A space-separated list of prim paths for the objects you want to act as hold-outs.
Rendersettings Primitive Path
The prim path of a USD Render Settings prim to use to set up the background and matte settings. The default is
/Render/rendersettings, which is the default for where the Karma render node looks for render settings. If this prim doesn’t already exist in the incoming stage, this node will create it.
The file path of the background image to use.
Horizontal and vertical scaling factors for the background image. These are normalized relative to the rendered image size, so for example a horizontal scale of
1 is the width of the rendered image.
Horziontal and vertical offsets for the background image. These are normalized relative to the rendered images size, so for example a horizontal offset of
0.25 moves the background image to the right 1/4 of the width of the rendered image.
Use Offscreen Texture
If the background plate does not perfectly cover the camera view, the “real” background (empty space) will show through. Use this to replace empty space with a texture. If you leave this off, the node will fill empty space with the Offscreen color instead.
When Use offscreen texture is on, the file path of the texture image to use to cover empty space.
When Use offscreen texture is on, this sets the rotation of the offscreen texture in 3D space.
When Use offscreen texture is off, the color to use for any “empty space” if the background plate does not fully cover the camera view.
Whether to record all holdout shadows in a single AOV, or generate a separate AOV for each Light Path Expression.
Generate an AOV for diffuse bounces on holdout objects.
Generate an AOV for light emissions on holdout objects.
Generate an AOV for glossy reflections on holdout objects.