Integral DVXi TS4 User Manual page 42

100 indicates 1 percent, 5000 indicates 50 percent, and so on. A brightness
change from black to white would be a change of 10000, or 100%.
This comparison is performed for all 330 blocks in the frames. The total
number of blocks that have changed is counted and used with the Percent-
age Area setting, as described in the following section.
PERCENTAGE AREA
The final step in motion detection is to compare the number of blocks that
have changed (as determined in the previous step) to the threshold com-
puted from the Percentage Area setting. If this threshold is reached, motion
is detected.
Percentage Area is the percentage of the 330 blocks in the image that need
to change for motion to be detected, multiplied by 100. For example, a
Percentage Area setting of 250 (2.5 percent) means that more than eight of
the blocks (.025×330) would have to change for motion to be detected. The
lowest setting you can use is about 30 (or 0.3 percent)—which requires a
single block in the image to change from the reference frame for motion to
be detected. Setting the Percentage Area smaller than 30 would require zero
blocks to change for motion to be detected—which means motion would be
detected all the time.
MASKING BLOCKS
Any of the 330 blocks in a frame can be masked. Whenever a block is
masked, it is completely ignored during the block-by-block comparison. A
masked block is never counted as one of the blocks that have changed even
if it changes completely from black to white. If you mask everything in the
picture, motion will never be detected no matter what happens.
Even if you mask one or more blocks, the Percentage Area setting uses all
330 blocks for its computations. For example, suppose you mask 230 blocks
and set Percentage Area to 2000. In this case, 20 percent of all 330 blocks—
or 66 blocks—must change for motion to be detected. However, this re-
quires 66 of the 100 unmasked blocks to change for motion to be detected.
PAL DIFFERENCES
The motion detection process is exactly the same for PAL, except that the
sizes are slightly different. In PAL, the original image is 768×576 and the
smaller black-and-white image is 22×18 (compared to 22×15 for NTSC).
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