ADS Technologies USBAV-708 INSTANT VIDEOMPX, Руководство пользователя

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Global motion compensation
Global motion compensation reduces the bit spend for motion estimation by
deriving the motion of some blocks from a global motion present in the frame, as
opposed to explicitly specifying a unique
vector for each.
Video sequences frequently contain
features such as panning and zooming
where many of the blocks will share a
common motion attributable to the
behavior of the camera.
Imagine the resulting effect on the
motion vectors if the camera were to pan right across a scene. It would be
reasonable to assume that many of the blocks would share a motion vector
opposite but relative to the panning motion of the camera, with the exception of
any blocks representing objects moving independently in the scene.
Likewise, if the camera were rotated clockwise all of the blocks representing a
static scene would appear to move anti-clockwise around the center of the
picture. If the camera were to zoom in, all blocks would appear to move outwards
from the center of the picture towards the edges. Its entirely possible that the
camera might zoom, rotate and pan at the same time.
During motion estimation, global motion compensation finds and records the
global motion attributable to translation, rotation and zooming of the camera.
Motion vectors for blocks whose motion is consistent with the global motion can
be calculated during decoding as opposed to being explicitly specified, and
hence less bits are spent recording motion vectors when global motion
compensation is enabled.
When global motion compensation is not used the encoder remains efficient in
recording translation. Each motion vector is recorded as the difference from the
vector of its neighboring block, thus when vectors are largely consistent
throughout a frame very few bits can be spent recording them.
What is global motion compensation?