Drawn mattes are useful when you have an irregularly shaped object that is in the screen that you want to matte out or preserve. As with surveyed mattes, there are a few types.
Creating Drawn Mattes
Click Add Drawn in the Holdout Mattes tab to create a drawn matte. A dialog box will appear with the name of the matte, the type, and the distance from the camera that the matte is generated at.
The matte itself is a planar object in 3D, and the points that are selected are its polygon border. When a matte endpoint is set into the yellow perimeter, the matte will extend out into space past the visible frame of the image for another 5 meters.
Click a series of points to draw the edge of the matte. To remove the last point clicked, press the Backspace key.
When a matte is created, the original viewing position and vector of the matte is saved, so moving the matte depth scales and translates the matte along the original camera orientation vector. In this way, the position of an object can be triangulated by drawing the object outline, then dollying the camera sideways and sliding the matte depth until the matte is again located on the object.
Completing Drawn Mattes
To complete the matte, either click in the yellow perimeter (extending the matte past the edge for 5 meters, or click the initial opening point. At this point, the screen on one side of the line or the other will highlight depending on whether the mouse is on one side or the other. Clicking in one state or another sets the matte ‘side’.
As with the garbage mattes, the active area of the matte is dark blue when the mattes are being shown.
The plane of the matte object is set normal to the camera direction when the matte is being drawn, at the distance specified in the dialog box. If the distance from the camera to the matte is measured and entered, the matte will track correctly in 3D space when the camera is moved.
Editing Points and Side
To edit an existing matte, highlight the matte name and click Edit. If the mouse is placed over an existing point in the matte, the point will highlight and can be dragged. Other controls:
- Add Points: To add a point on a line, double click the line.
- Remove Points: To remove a point, highlight it, select it, and press Backspace.
- Change Matte Side: To change the matte side, deselect all points by clicking anywhere on the preview screen, then press Backspace.
- Matte Depth: To change the 3D position of the matte, drag or enter a new number into the depth dialog. As the matte moves further from the camera, it is automatically scaled to maintain the correct drawn position. You can see this more clearly in Observer View.