Apple Shake 4 - Manual (Page 731)

Chapter 25 Image Tracking, Stabilization, and SmoothCam 731
Manually Coax Your Track
Another technique you can use is to manually insert tracking keyframes. For example, if
you have 100 frames to track, you can put in a keyframe every 5 or 10 frames with the
Autokey feature. A helpful trick is to set an increment of 5 or 10 in the Time Bar. Press
the Left Arrow or Right Arrow to jump by the increment amount.
Note: To add a keyframe without moving an onscreen control—for example, to create
a keyframe at frame 20 with the same value as a keyframe at frame 19—turn Autokey
off and then back on.
Once your keyframes are manually entered, return to frame 1, and set the
failureBehavior to “use existing key to predict location.” The tracker searches along the
tracker’s preexisting motion path to find matching patterns.
Identify the Color Channel With the Highest Contrast
The tracker works best with a high-contrast reference pattern. The human eye sees
contrast as represented by value. However, you may sometimes have higher contrast in
saturation or hue, so switch to a different color space with the matchSpace parameter
in the tolerances subtree. A shot may also have a higher contrast in a specific RGB
channel than in the other channels. For example, the blue channel may have a larger
range than the red or green channel. In such a case, apply a Color–Reorder node to the
image, set the channels parameter to bbb, and then perform the track with luminance
selected as the matchSpace.
Delog Logarithmic Cineon Files Prior to Tracking
Because the logarithmic to linear conversion increases contrast, you may have better
results on linear data than on logarithmic data.
Avoid Reducing Image Quality
Ideally, you should track an image with the most amount of raw data. This means if you
apply a Brightness node set to .5 to your image, you lose half of the color information
that could have been used for tracking. It is far better to track the image before the
Brightness function is applied.
Do Not Track Proxies
Don’t ever track an image with proxy settings enabled. Proxies are bad for two
reasons: First, you filter the image so detail is lost. Second, you automatically throw
data away because of data round-off. For example, if using 1/4 proxy, you automatically
throw away four pixels of data in any direction, which means an 8 x 8 grid of potential
inaccuracy.