Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1997-12-18
2001-03-06
Britton, Howard (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C348S716000, C348S718000, C375S240150, C375S240250
Reexamination Certificate
active
06198773
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to video memory management in MPEG (“Moving Picture Experts Groups”) decode and display system, and more particularly to reducing the size of video memory needed in a MPEG decode and display system for decoding and displaying video images.
In the late 1980s, a need arose to place motion video and its associated audio onto first generation CD-ROMs at 1.4 Mbits/s. For this purpose, in the late 1980s and early 1990s, the ISO (“International Organization for Standardization”) MPEG committee developed digital compression standards for the video and two-channel stereo audio. The standard is known colloquially as MPEG-1 and officially as ISO 11172.
Following MPEG-1, the need arose to compress entertainment TV for such transmission media as satellite, cassette tape, over-the-air, and CATV. Thus, to have available digital compression methods for full-resolution Standard Definition TV (SDTV) pictures or High Definition TV (HDTV) pictures, ISO developed a second standard known colloquially as MPEG-2 and officially ISO 13818. The bitrate chosen for optimizing MPEG-2 was 4 Mbits/s and 9 Mbits/s for SDTV and about 20 Mbits/s for HDTV.
Neither the MPEG-1 nor the MPEG-2 standards prescribe which encoding methods to use, the encoding process, or details of encoders. These standards only specify formats for representing data input to the decoder, and a set of rules for interpreting these data. These formats for representing data are referred to as syntax and can be used to construct various kinds of valid data streams referred to as bitstreams. The rules for interpreting the data are called decoding semantics. An ordered set of decoding semantics is referred to as a decoding process.
The MPEG syntax supports different encoding methods that exploit both spatial redundancies and temporal redundancies. Spatial redundancies are exploited by using block-based Discrete Cosine Transform (“DCT”) coding of 8×8 pixel blocks followed by quantization, zigzag scan, and variable length coding of runs of zero quantized indices and amplitudes of these indices. Quantization matrix allowing perceptually weighted quantization of DCT coefficients can be used to discard perceptually irrelevant information, thus increasing the coding efficiency further. On the other hand, temporal redundancies are exploited by using motion compensated prediction, forward prediction, backward prediction, and bidirectional prediction.
The MPEG provides two types of video data compression method: intraframe coding, and interframe coding.
The intraframe coding is for exploiting the spatial redundancies. Many of the interactive requirements can be satisfied by the intraframe coding alone. However, in some video signals with low bitrates, the image quality that can be achieved by intraframe coding alone is not sufficient.
Therefore, the temporal redundancy is exploited by MPEG algorithms which compute an interframe difference signal called the Prediction Error. In computing the prediction error, the technique of motion compensation is employed to correct the prediction for motion. As in H.261, the Macroblock (MB) approach is adopted for motion compensation in MPEG. In unidirectional motion estimation, called Forward Prediction, a Target MB in the picture to be encoded is matched with a set of displaced macroblocks of the same size in a past picture called the Reference picture. As in H.261, the Macroblock in the Reference picture that best matches the Target Macroblock is used as the Prediction MB. The prediction error is then computed as the difference between the Target Macroblock and the Prediction Macroblock.
I. PICTURE BUFFER SIZE
(1) Two Reference Frames
In summary, MPEG-2 divides video pictures into three types of pictures (i.e. Intra “I”, Predictive “P”, & Bidirectionally Predictive “B”). By definition, all macroblocks within an I picture must be coded intra (like a baseline JPEG picture). Additionally, macroblocks within a P picture may either be coded as intra or non-intra. During the non-intra coding of a P picture, the P picture is temporally predicted from a previously reconstructed picture so that it is coded with respect to immediately previous I or P pictures. Finally, macroblocks within the B (i.e. bidirectionally predictive) picture can be independently selected as either intra, or non-intra such as forward predicted, backward predicted, or both forward and backward (Interpolated) predicted. During the non-intra coding of a B picture, the picture is coded with respect to the immediate previous I or P picture, as well as the immediate next I or P picture. In terms of coding order, P pictures are causal, whereas B pictures are noncausal and use two surrounding casually coded pictures for prediction. In terms of compression efficiency, I pictures are least efficient, P pictures are somewhat better, and B pictures are the most efficient.
All the macroblocks headers contain an element, called macroblock_type, which can flip these modes on and off like switches. The macroblock (or motion_type as in MPEG-2) type is possibly the single most powerful element in the whole of video syntax. Picture types (I, P, and B) merely enable macroblock modes by widening the scope of the semantics.
The sequence of pictures may consist of almost any pattern of I, P, and B pictures. It is common in industrial practice to have a fixed pattern (e.g. IBBPBBPBBPBBPBB), however, more advanced encoders will attempt to optimize the placement of the three picture types according to local sequence characteristics in the context of more global characteristics.
As explained above, since the decoder needs the two reference frames (i.e. 2 P frames; 1 P and 1 I frames; or 2 I frames) to reconstruct a B picture, the video decode and display system must allocate at least two frames of video memory to store the two reference frames.
(2) Two Half-Frames
(I) Interlaced Video
In addition, MPEG-2 defines that a frame may be coded progressively or interlaced, signaled by the “progressive_frame” variable.
Progressive frames are a logic choice for video material which organized from film, where all “pixels” are integrated or captured at almost the same time instant. The optical image of a scene on the picture is scanned one line at a time from left to right and from top to bottom. The detail that can be represented in the vertical direction is limited by the number of scan lines. Thus, some of the detail in vertical resolution is lost as the result of raster scanning fall. Similarly, some of the detail in the horizontal direction is lost owing to sampling of each scan line.
The choice of scan lines involves tradeoff among contradictory requirements of bandwidth, flicker and resolution. Interlaced frames scanning tries to achieve these tradeoffs by using frames that are composed of two fields sampled at different times, with lines of the two fields interleaved, such that two consecutive lines of a frame belong to alternate fields. This represents a vertical-temporal tradeoff in spatial and temporal resolution.
For the interlaced pictures, MPEG-2 provides a choice of two “Picture Structures.” “Field-pictures” consist of individual fields that are each divided into macroblocks and coded separately. With “Frame-pictures”, on the other hand, each interlaced field pair is interleaved together into a frame that is then divided into macroblocks and coded. MPEG-2 requires interlaced video to be displayed as alternate top and bottom fields. However, within a frame either the top or bottom field is temporally coded first and sent as the first Field-picture of the frame. The choice of the frame structures is indicated by the one of the MPEG-2 parameters.
In a conventional decode and display system processing interlaced Frame-pictures, even though both the reconstructured data for the top field and the bottom field are generated by the decoder simultaneously, the bottom field is displayed only after the completion of the displaying of the top field, or vice versa. Because of this delay in displaying the bott
Anisman David
Fraenkel Miri
Gill Aharon
Goldberg Paul R.
Ironi Alon
Britton Howard
Skjerven Morrill & MacPherson LLP
Zoran Corporation
LandOfFree
Video memory management for MPEG video decode and display... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Video memory management for MPEG video decode and display..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Video memory management for MPEG video decode and display... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2514665