Canon Camera Hackers Manual page 186

Fast movements
The settings for fast movements are similar to those for lightning. We use
a slightly finer grid (4x6) and discard the border grid cells, so movements at
the very border of the image are ignored. After the motion is detected, we
allow for a small delay of 100 milliseconds for camera calibration. The
threshold is determined from the brightness value measured by the
camera, but with a higher sensitivity than normal. Because conditions may
change rapidly, we set the time-out to 30 seconds so that the camera can
more frequently adapt to altered conditions.
Small objects
The next program is used for detecting rather small movements or move-
ments of small objects. For example, it is sufficiently sensitive to detect the
movement of a hand in group photos.
This is possible by using a very fine grid of 12x12 = 144 cells. Again we
discard the cells at the borders of the image. Motion detection with such a
high number of cells performs much more slowly. We therefore adapt the
other parameters of the program to slow operation. By using a subsam-
pling value of 1, we analyze each single pixel, resulting in slower operation
but working much more accurately. The program will catch slower move-
ments than the previous programs because of a detection interval of
50 milliseconds. Finally, we focus immediately before the shot (u=0) if a
fixed distance was not set in parameter u. Focusing immediately before the
shot would not be suitable for fast movements (because it takes too long),
but it results in more precisely focused images.
Macro
The macro program has a 5x5 grid where only the center cell is used for
detection; all other cells are discarded. Only those movements happening
in the very center of the image will be detected. Movements in the outer
areas—typically movements of branches and leaves—are ignored. For the
same reason, we only observe changes in the red channel (c=3). Move-
ments of dominantly green foliage will be ignored, while movements of
small red, orange, or brown subjects will be detected.
You may want to use a fixed subject distance (u=...) for this program
or switch the camera to Macro Mode.
5.7 Example scripts
177