Apple MA434Z/A User Manual - Page 752

• update every frame: The source sample is updated from the previous frame. This usually creates an inherent drift in the track, as tiny errors accumulate. This method is for movements that have drastic changes in perspective and scale. • update from keyframes: If you are using a failureBehavior of "predict location and don't create keys" or "don't predict location," a keyframe is not necessarily saved every frame. In this case, you may only want to update from the last frame with a valid keyframe. • update if above reference tolerance: This option updates the reference sample from the previous frame if the correlation is above the referenceTolerance. The intent is to update every frame unless you know the point is obscured. If you use a predict mode and know there are obstructions, this option keeps the reference area from updating if the point is completely obscured. • update if below reference tolerance: This option updates the reference sample from the previous frame if the correlation is below the referenceTolerance. This option basically says, "If I can't get a good match, then resample." It is excellent for gradual perspective and scale shifts in the tracking area. failureTolerance If the correlation value of the tracker's analysis falls below the value in this field, Shake initiates the failureBehavior. failureBehavior A pop-up menu containing the following settings: • stop: The tracker stops if the correlation is less than the failureTolerance. You can also press Esc to manually stop tracking. • predict location and create key: If a failure is detected, then the tracker predicts the location of the keyframe based on a vector of the last two keyframes, then continues tracking in the new area. • predict location and don't create key: Same as above, but this option merely predicts the new search area and does not create new keyframes until a high correlation is obtained. This option is excellent for tracked objects that pass behind foreground objects. • don't predict location: In this case, the tracker merely sits in the same spot looking for new samples. New keyframes are not created. • use existing key to predict location: This allows you to manually create keyframes along your track path. You then return to the start frame and start tracking. The search pattern starts looking where the preexisting motion path is. limitProcessing This button creates a Domain of Definition (DOD) around the bounding boxes of all active trackers. Only that portion of the image is loaded from disk when tracking, so the track is faster. This setting has no effect on the final output image. 752 Chapter 25 Image Tracking, Stabilization, and SmoothCam