Apple MA434Z/A User Manual - Page 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. Chapter 25 Image Tracking, Stabilization, and SmoothCam 731