In global motion compensation, the motion model basically reflects camera motions such as:
- Dolly - moving the camera forward or backward
- Track - moving the camera left or right
- Boom - moving the camera up or down
- Pan - rotating the camera around its Y axis, moving the view left or right
- Tilt - rotating the camera around its X axis, moving the view up or down
- Roll - rotating the camera around the view axis
It works best for still scenes without moving objects.
There are several advantages of global motion compensation:
- It models the dominant motion usually found in video sequences with just a few parameters. The share in bit-rate of these parameters is negligible.
- It does not partition the frames. This avoids artifacts at partition borders.
- A straight line (in the time direction) of pixels with equal spatial positions in the frame corresponds to a continuously moving point in the real scene. Other MC schemes introduce discontinuities in the time direction.
MPEG-4 ASP supports GMC with three reference points, although some implementations can only make use of one. A single reference point only allows for translational motion which for its relatively large performance cost provides little advantage over block based motion compensation.
Moving objects within a frame are not sufficiently represented by global motion compensation. Thus, local motion estimation is also needed.
Read more about this topic: Motion Compensation
Famous quotes containing the words global, motion and/or compensation:
“The Sage of Toronto ... spent several decades marveling at the numerous freedoms created by a global village instantly and effortlessly accessible to all. Villages, unlike towns, have always been ruled by conformism, isolation, petty surveillance, boredom and repetitive malicious gossip about the same families. Which is a precise enough description of the global spectacles present vulgarity.”
—Guy Debord (b. 1931)
“It is the fixed that horrifies us, the fixed that assails us with the tremendous force of mindlessness. The fixed is a Mason jar, and we cant beat it open. ...The fixed is a world without fire--dead flint, dead tinder, and nowhere a spark. It is motion without direction, force without power, the aimless procession of caterpillars round the rim of a vase, and I hate it because at any moment I myself might step to that charmed and glistening thread.”
—Annie Dillard (b. 1945)
“The compensation of a very early success is a conviction that life is a romantic matter. In the best sense one stays young.”
—F. Scott Fitzgerald (18961940)