The Transform Clip node can be used to crop, resize and rotate a clip. Some examples where this node can be useful are:
to separate out the left and right eye images in a stereo shot which have been combined into a single frame
to resize a clip which, combined with a downstream Cache node, allows for proxy resolution processing.
Note: Great care should be taken when using this node since a clip can easily be modified such that it is no longer possible to extract a camera track from it since certain assumptions the software makes about the clip are no longer true. If, for example, you crop a clip such that only a certain sub-portion of it forms the output image, then the optical centre of the image wil change, which may adversely affect performance in downstream nodes.
Another operation this node can perform which potentially impacts the ability to track it is a non-uniform resize of the clip since this will change the effective pixel aspect ratio.
While the camera tracking algorithms are tolerant to some degree to these sorts of changes, do not use this node without consideration as to what the implications are to the underlying virtual camera model that PFTrack is using.
The node takes a rectangular portion of the input clip and copies this, potentially with scaling and rotation, to form the output clip.
The node editor is split into two sections. The left most section contains the parameters controlling which rectangular portion of the input clip forms the output clip. The right most section contains the parameters controlling the output clip itself.
The Cinema window always shows the output clip.
X offset, Y offset, Width, Height: The rectangular portion of the input clip to use as the output clip. This rectangle is bound by the input clip resolution which is detailed above the controls. The R button next to each control resets the particular parameter to its original value (although width and height may be constrained by the X and Y offset values).
Width, Height: The resolution of the output image. The R button next to each control resets the particular value to the width and height of input clip rectangle.
Pixel aspect: The pixel aspect ratio of the output clip. The options are Pass through where the pixel aspect ratio is passed through unmodified from the input clip to the output clip; Calculate where the output pixel aspect ratio is calculated to be the input clip's pixel aspect ratio modified by any resizing the node performs; and Specify where the output pixel aspect ratio is a user-specified value. The numeric edit box next to this control shows the current pixel aspect ratio value.
Rotate: The rotation of the image by 0, 90, 180 and 270 degrees.
Flip: When enabled, performs a vertical flip of the image.
Flop: When enabled, performs a horizontal flip of the image.