Global motion compensation

Global motion compensation

"Global motion compensation" "(GMC)" is a technique used in video compression to reduce the bitrate required to encode video. It is most commonly used in MPEG-4 ASP, such as with the DivX and Xvid codecs.

Operation

Global motion compensation describes the motion in a scene based on a single affine transform instruction. The reference frame is panned, rotated and zoomed in accordance to GMC "warp points" to create a prediction of how the following frame will look. Since this operation works on individual pixels (rather than blocks), it is capable of creating predictions that are not possible using block-based approaches.

Each macroblock in such a frame can be compensated using global motion (no further motion information is then signalled) or, alternatively, local motion (as if GMC was off). This choice, while costing an additional bit per macroblock, can improve prediction quality and therefore reduce residual.

Because the transforms used in global motion compensation are only added to the encoding stream when used, they do not have a constant bitrate overhead. A predicted frame which uses GMC is called an S-frame ("sprite" frame) while a predicted frame encoded without GMC is called either a P-frame, if it was predicted purely by previous ("past") frames, or a B-frame if it was predicted jointly with past and later ("future") frames (an unpredicted frame encoded as a whole image is referred to as anI-frame).

Implementations

DivX has only one GMC "warp point" specified. This enables easier hardware implementation, but limits the global transform to panning operation only. Since panning can be described using blocks, this implementation rarely improves video quality.

Xvid allows up to 3 warp points, and as a result, has less hardware support. The DivX player, however, does support 3-warp-point GMC, and thus will play GMC Xvid-encoded streams.

Hardware compatibility

Due to the extra decoding CPU cost of global motion compensation, most hardware players do not support global motion compensation. One example is the Creative Zen Vision M, which supports Xvid and DivX encoded video, but only with GMC disabled.

ee also

*Divx
*MPEG-4 ASP
*Motion compensation
*Xvid


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Global Motion Compensation — Unter dem Oberbegriff Motion Compensation oder Motion Prediction (wortwörtlich: Bewegungsvorhersage) wird eine Reihe von Algorithmen zusammengefasst, die hauptsächlich unterstützend bei der Videokompression eingesetzt werden. Die temporären… …   Deutsch Wikipedia

  • Motion compensation — is an algorithmic technique employed in the encoding of video data for video compression, for example in the generation of MPEG 2 files. Motion compensation describes a picture in terms of the transformation of a reference picture to the current… …   Wikipedia

  • Motion Compensation — Visualisierte Bewegungsvektoren der MPEG Kodierung über einem Standbild aus Elephants Dream. Erkennbar sind die Bewegungen der verschiedenen Plattformen und Körperteile der Figur. Unter dem Oberbegriff Motion Compensation oder Motion Prediction… …   Deutsch Wikipedia

  • Quarter Pixel Motion Compensation — Unter dem Oberbegriff Motion Compensation oder Motion Prediction (wortwörtlich: Bewegungsvorhersage) wird eine Reihe von Algorithmen zusammengefasst, die hauptsächlich unterstützend bei der Videokompression eingesetzt werden. Die temporären… …   Deutsch Wikipedia

  • Motion Prediction — Unter dem Oberbegriff Motion Compensation oder Motion Prediction (wortwörtlich: Bewegungsvorhersage) wird eine Reihe von Algorithmen zusammengefasst, die hauptsächlich unterstützend bei der Videokompression eingesetzt werden. Die temporären… …   Deutsch Wikipedia

  • Motion estimation — is the process of determining motion vectors that describe the transformation from one 2D image to another; usually from adjacent frames in a video sequence. It is an ill posed problem as the motion is in three dimensions but the images are a… …   Wikipedia

  • Motion JPEG — In multimedia, Motion JPEG (M JPEG) is an informal name for a class of video formats where each video frame or interlaced field of a digital video sequence is separately compressed as a JPEG image. Originally developed for multimedia PC… …   Wikipedia

  • Mars Global Surveyor — Artist s conception of Mars Global Surveyor Operator NASA Major contractors Orbiter Satellite of …   Wikipedia

  • Teamwork Motion Pictures Ltd. — Teamwork Motion Pictures Ltd. (Traditional Chinese: 天幕製作有限公司) is a former Hong Kong film production company. The company was established by Cantopop star, actor and film producer Andy Lau.EstablishmentTeamwork was established in 1991 by… …   Wikipedia

  • Bewegungsprädiktion — Unter dem Oberbegriff Motion Compensation oder Motion Prediction (wortwörtlich: Bewegungsvorhersage) wird eine Reihe von Algorithmen zusammengefasst, die hauptsächlich unterstützend bei der Videokompression eingesetzt werden. Die temporären… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”