Eyeon:Manual/Fusion 6/Catcher
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The Catcher material is used to "catch" texture-mode projections cast from Projector 3D and Camera 3D tools. The intercepted projections are converted into a texture map and applied by the Catcher material to the geometry it is connected to.
To understand the purpose of the Catcher tool it helps to understand the difference between light based projections and texture based projections. A light based projection 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 the artist wishes to project an image of a building onto an image plane as part of a set extension shot. The artist has first rotoscoped the image to matte out the windows. This will make it possible to see 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 matted 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 from light or ambient light mode to texture mode, Fusion knows to apply the projected image as a texture map. When using this technique, 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 is that the Catcher can be used to project alpha onto an object, and that 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 that the Catcher material requires a Projector 3D or Camera 3D tool in the scene, set to project an image in Texture mode on the object the Catcher is connected to. Without a projection, or if the projection is not set to Texture mode, the Catcher will simply make the object transparent and invisible.
External Inputs
This material tool does not have any external inputs.
Controls
Use this checkbox to enable or disable the tool.
The color accumulation mode is used to control how the Catcher will combine the light from multiple projectors. It will have no affect on the results when only one projector is in the scene. This control is designed to work with the Software renderer, and will have no affect when using the OpenGL renderer.
The color accumulation mode is used to control how the Catcher will combine the alpha channels from multiple projectors. It will have no affect on the results when only one projector is in the scene. This control is designed to work with the Software renderer, and will have no affect when using the OpenGL renderer.
The accumulation threshold can be used to exclude certain low values from the accumulation calculation. For example, when using the median accumulation mode, a threshold of 0.01 would exclude any pixel with a value of less than 0.01 from the median calculation.
When active the Catcher will only receive light from Projectors with a matching ID. Projectors with a different ID will be ignored.
This slider sets the numeric identifier assigned to this material. This value will be rendered into the MatID auxiliary channel if the according option is enabled in the renderer.
Tips for Catcher (edit)
- How to render soft shadows using the SW-renderer and depth of field using the OGL-renderer? An example comp by Eric Westphal can be found in this pigsfly thread.
- The Blend accumulation mode (available since Fusion 6.1) will perform an additive merge of multiple projectors. For this to work you need to define a projector priority for each Projector3D or Camera3D. Higher priorities are considered on top of projections that have lower priorities. These foreground projections should have an alpha channel with transparent parts where the background projections will show through.
- The OpenGL renderer currently doesn't support all the accumulation modes. For "Blend" mode, you need the software renderer. However, you can merge multiple catcher materials (using different projector IDs) using the Material Merge. This will work in OpenGL (example comp)
- When using the software renderer, the catcher tool will fill pixels outside of the projector's frustum with the canvas color of the image that is being projected.
| I Am Fusion - Projection Tutorial
This video shows how to align and layer projections using multiple cameras. Watch it on YouTube. |
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