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Match moving is primarily used to track the movements of a camera through a shot so that an identical virtual camera move can be produced in a 3D animation program. When new animated elements are composited back into the original live action shot they will appear in perfectly matched perspective and therefore appears seamless.
Match moving allows the insertion of computer graphics into live action footage with correct position, scale, orientation, and motion relative to photographed objects in the shot. The term is used loosely to refer to several ways of extracting motion information from a motion picture, particularly camera movement.
The process of tracking can be broken down into two steps.
1. The first step is identifying and tracking features. A feature is a specific point in an image that a tracking algorithm can lock onto and follow through multiple frames. Often features are selected because they are bright or dark spots, edges or corners, depending on the particular tracking algorithm. What is important is that each feature represents a specific point on a surface of a real object. As a feature is tracked it becomes a series of two dimensional co-ordinates that represent the position of the feature across a series of frames. This series is referred to as track. Once tracks have been created they can be used immediately for 2d motion tracking or then be used to calculate the 3D information.
2. The second step involves solving for 3D motion. The process attempts to drive the motion of the camera by solving the inverse projection of the 2D paths for the position of the camera. This process is referred to as a calibration. When a point on the surface of a three dimensional object is photographed its position in the 2D frame can be calculated by a 3D projection function. We can consider the camera to be an abstraction that holds all the parameters necessary to model a camera in a real or virtual word. Therefore a camera is a vector that includes as it elements the position of the camera its orientation, focal length and other possible parameters that defines how the camera focuses light onto the film plane. These parameters help in generating a huge bunch of points in a 3D environment, according to the position of the objects in the footage. These bunch of points are sometimes referred to as point clouds.
Example of Match Moving in PF Track
Example of 2D Tracking in After Effects
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- Check if there is enough information in the footage for the tracking markers to hold on.
- If there is not much information for the tracking markers to stick onto the footage, start playing around with the footage manipulation settings, to bring out the information from the footage for the automatic trackers to hold onto the footage.
- Mask out the highly contrasted points on the edge of the footage, as they can produce many tracking points jumping on and off on the edge of the footage. These tracking points can stay stick over the edges looking for the contrast between white and black. So to fix that we need to stop the tracking points from going towards the edge of the frame by putting some dummy masks.
- Look for the objects in the scene that can help us for scene orientation. Pick an object with the horizontal line and draw an X axis line over that object, which will help our camera solution to automatically generate the ground plane orientation. Similarly drawing orientation lines over the objects with Y and Z information in the footage will further refine the camera solution.
- Set the tracking parameters according to the footage requirements.
- Start the automatic tracking and solving the camera together with track and solve.
- Right click on one of the tracking points on the ground plane and select set as origin, to define it as the origin point of the world.
Garbage Mask for the moving car object and Dummy Mask for the highly contrasted points of the Horizon.
X Y and Z axis line for scene orientation.
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