Apple MA434Z/A User Manual - Page 730

The following example shows a track marker placed on a TV screen so the client could place an image on the TV. The default tracker reference pattern is unnecessarily large. The only interesting detail is the black cross in the middle. Otherwise, most of the pattern matches up with most of the rest of the image-green. To adjust for this, limit the reference pattern to more closely match the black crosshairs. Default tracker reference pattern Adjusted tracker reference pattern Picking a Good Search Region You should also suit your search region to match the clip's movement and the patterns near the reference pattern. With the default settings, the bus example clip does not track the lower-left corner of the sign very well. This is because the middle black horizontal line can easily be matched with the black line at the very base of the search region in later frames of the clip. The X axis is squeezed so much that vertical details disappear. Additionally, since the bus is moving to the right, there is no point in wasting cycles to the left of the point. Remember, the larger the search region, the more samples the tracker must take. The corrected search region, illustrated below, is now high enough to not include the lower black line, and extends minimally to the left. 730 Chapter 25 Image Tracking, Stabilization, and SmoothCam