Keyframes are specific frames for which the system first computes the camera parameters and 3D points using a powerful optimization process. Once keyframes and 3D points are computed, the system computes the intermediate frames by first interpolating between the keyframes, as in a standard animation package, then refining the camera parameters using the estimated 3D point information.

MatchMover chooses automatically the keyframes to compute using the following criteria:

• If the focal length is known, at least four 3D points are needed.
• If the focal length is unknown, at least six 3D points are needed. These points should not all lie on the same plane.

In most situations the keyframes chosen by MatchMover are sufficient, however in some cases (e.g. where there is jagged camera motion), it can be useful to position the keyframes manually.

By default, keyframes, and indeed reference frames are chosen automatically. The number of keyframes is determined by the keyframe Step value and Maximum keyframes value. The keyframe Step value is the maximum number of frames between each keyframe. A low step value gives a higher accuracy, but computation is slower. See Reference frames.

The Maximum keyframes value determines the highest number of non-automatic keyframes allowed in a sequence. This value is only an indication, as the number of keyframes generated may be larger, especially in shots where a large number of points enter or leave the image.