IBM SG24-4817-00 manual Motion Interpretation and Improved Compression

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4.6.1.3 Motion Interpretation and Improved Compression

MPEG-2 interprets motion between successive images and takes advantage of motion to improve compression while sustaining the same level of perceived image quality. The MPEG-2 motion interpretation uses a combination of two kinds of frames to do this:

•An anchor frame:

−Intra-Frame (I-Frame):

-Only exploits spatial redundancy to compress information within the frame

-Contains all information to reconstruct the image; does not depend on another frame

•A difference frame, which can be either:

−Predictive Frame (P-Frame):

-Exploits temporal and spatial redundancy to compress video frame

-Must reference a previous anchor frame to reconstruct the image

-Can be anchors to other P or B frames

−Bidirectionally Predictive Frame (B-Frame)

-Exploits temporal and spatial redundancy to compress video frame

-Must reference an anchor frame

-Cannot be an anchor to another frame

A typical encoded frame sequence might look like the one in Figure 19 on page 51.

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