User Manual

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Catcher [3CA]
The Catcher node
Catcher Node Overview
The Catcher material is used to “catch” texture-mode projections cast from Projector 3D and
Camera 3D nodes. The intercepted projections are converted into a texture map and applied
by the Catcher material to the geometry to which it is connected.
To understand the Catcher node, it helps to understand the difference between light-based
projections and texture-based projections. Choosing Light from the projection mode menu on
the Projector 3D or Camera 3D nodes simply adds the values of the RGB channels in the
projected image to the diffuse texture of any geometry that lies within the projection cone. This
makes it impossible to clip away geometry based on the Alpha channel of an image when using
light mode projections.
Imagine a scenario where you want to project an image of a building onto an image plane as
part of a set extension shot. You first rotoscope the image to mask out the windows. This makes
it possible to see the geometry of the rooms behind the wall in the final composite. When this
image is projected as light, the Alpha channel is ignored, so the masked windows
remain opaque.
By connecting the Catcher to the diffuse texture map of the material applied to the image plane,
and then switching the projection mode menu in the Projector 3D or Camera 3D node from
Light or Ambient Light mode to Texture mode, the projected image is applied as a texture map.
When using this technique for the example above, the windows would become transparent, and
it would be possible to see the geometry behind the window.
The main advantages of this approach over light projection are that the Catcher can be used to
project Alpha onto an object, and it doesn‘t require lighting to be enabled. Another advantage
is that the Catcher is not restricted to the diffuse input of a material, making it possible to project
specular intensity maps, or even reflection and refraction maps.
NOTE: The Catcher material requires a Projector 3D or Camera 3D node in the scene,
set to project an image in Texture mode on the object to which the Catcher is
connected. Without a projection, or if the projection is not set to Texture mode, the
Catcher simply makes the object transparent and invisible.
Inputs
The Catcher node has no inputs. The output of the node is connected to the the diffuse color
material input of the Blinn, Cook Torrance, or other material node applied to the 3D geometry.
Chapter – 83 3D Texture Nodes 1799