Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-02-11
2002-04-16
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C382S245000, C341S059000
Reexamination Certificate
active
06373905
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a decoding apparatus and a decoding method for use in a process for reproducing a moving picture stored in a storage device.
BACKGROUND OF THE INVENTION
In recent years, as an information society greatly advances, a demand for sending moving pictures to other people beyond time and places goes on increasing. In response to this demand, it became possible to record and reproduce the moving pictures by the use of a recording apparatus or transmit them via a communication network over a long distance. A digital technology is employed to transmit/store these information in communication. Also, a coding method using the digital technology is adopted in broadcasting.
For recording a moving picture or an audio signal in a digital format (digital signal), a digital recording medium of a large capacity is used. As available digital recording media, there are a video CD (Compact Disc) which has digital moving pictures recorded in a CD, and a DVD which contains higher-quality and longer digital moving pictures than that recorded in the video CD.
However, these digital recording media do not have storage capacities sufficient to record the moving picture for a long time period. It is therefore essential that a technique for coding the digital signal efficiently (compressing data) be employed in order to transmit and record the moving picture or the audio signal efficiently.
The technique for coding the moving picture or the audio signal has been developed. Currently, methods according to an international standard relating to “Information Technology—Coding of moving pictures and associated audio for digital storage media at up to about 1.5 Mbits/s (ISO/IEC11172-2)” are used. The international standard is termed “MPEG” (Moving Picture Experts Group).
A description will be given of a method for coding a digital moving picture and a bitstream according to MPEG.
FIG.
6
(
a
) shows the digital moving picture according to MPEG. A video frame group
500
called “sequence” comprising a series of video frames
700
is coded. The sequence is commonly divided into a series of video frame groups
600
, each of which is called a group of pictures (GOP) of about 0.5 second.
FIG.
6
(
b
) shows an example of the GOP. As shown in FIG.
6
(
b
), the GOP is composed of I pictures, P pictures, and B pictures. The I picture is obtained by independently coding data corresponding to a video frame, (the data is coded entirely by itself), and called an “intra-picture”. The P picture is predicted from a temporally previous (forward) frame (I picture or P picture) and is called a “forward predictive picture”. The B picture is predicted from temporally previous and subsequent (forward and backward) frames (I or P pictures), that is, by interpolation between previous and subsequent I or P pictures, and is called a “bidirectionally Predictive Picture”.
FIG.
7
(
a
) shows a structure of each picture. Each picture comprises a series of band-shaped regions on a frame which are called “slices” (one or more slices). Each slice comprises one or more “macroblocks” each composed of (16×16) pixels.
FIG.
7
(
b
) shows an example of a macroblock
800
. The macroblock
800
comprise a plurality of image blocks each composed of (8×8) pixels shown in FIG.
7
(
c
). The macroblock shown in FIG.
7
(
b
) comprises 4 blocks corresponding to a luminance signal Y, and 2 blocks corresponding to chrominance signals Cb and Cr. The chrominance signals Cb and Cr each comprises pixels sampled from an original image at a resolution as half as a resolution at which pixels are sampled therefrom to form the luminance signal Y.
In the above hierarchical (layered) structure, sequences, GOPs, pictures, and slices as upper layers are respectively provided with headers each containing hierarchy information. Each header comprises a code sequence called a start code comprising “0s” of 23 bits or more and the following “1” of 1 bit which are uniquely identifiable on a bitstream, coding information about each layer, extension indicating information about extension from MPEG to MPEG2 (Information Technology—Generic coding of moving pictures and associated audio for digital information (ISO/IEC13818-2), and the like.
FIG. 8
shows an example of a structure of the bitstream. Turning to
FIG. 8
, in the macroblock (lower) layer, various types of image coding information is shown. From the head, aligned are a macroblock address increment indicating a distance from a previously (most recently) coded macroblock with respect to a two-dimensional point in a picture, a macroblock type indicating coding mode information about a macroblock type indicating coding mode information about a macroblock to be coded, a quantiser scale indicating a quantisation scale, motion vectors for use in motion compensation, a coded block pattern indicating which coded block data is present in the bitstream, coded DCT (Discrete Cosine Transform) coefficient data, and the like.
Each of these data is represented as a variable length code. To data appearing more frequently, a code of shorter length is assigned. Thereby, these data which occupies most of the bitstream is efficiently coded.
To be specific, the bitstream comprising the sequence (lower) layer is, as shown in
FIG. 9
, divided in units of fixed length, and stored in the payloads of packets. To each of these payloads, added is a packet header composed of fields such as a packet start code, a stream identifier (ID), a packet length, a PTS (Presentation Time Stamp), a DTS (Decoding Time Stamp), and the like. These packets are multiplexed to create the bitstream.
The data so coded is stored in the digital recording medium such as the video CD or the DVD and then processed by a decoding apparatus, to reproduce a moving picture.
It is essential that the decoding apparatus using the digital storage medium have a capability of reproducing moving pictures in the order as recorded and a capability of performing trick play including fast forward playback and fast rewind playback. Hereinafter, a description will be given of a method for playing back the bitstream by the fast forward playback or the fast rewind playback.
In a normal playback process, all the pictures included in the bitstream are decoded and displayed, while in the fast forward playback process, an image is displayed by any of the following methods. One method is to transfer the bitstream recorded in the digital storage medium to the decoding apparatus, which decodes only the T pictures to be displayed. The other method is to selectively transfer packets containing I picture information from the digital storage medium to the decoding apparatus, which decodes the I pictures to be displayed.
In actuality, there are drawbacks with the use of the former method, including lack of the decoding apparatus's ability to analyze the bitstream and complicated selection of the I pictures, and therefore, the latter method is commonly used for the fast forward playback process. For instance, when the decoding apparatus reproduces the pictures according to the former method, assuming that the speed of the fast forward playback process is 100 times as high as that of the normal playback process, it requires an ability to analyze the bitstream 100 times as high as that of the decoding apparatus in the normal playback process. Hence, a general decoding apparatus does not satisfy such performance requirements.
Subsequently, a description will be given of the latter decoding method with reference to FIGS.
10
(
a
)-
10
(
c
). FIG.
10
(
a
) shows a bitstream on the digital storage medium. FIG.
10
(
b
) shows parts of the bitstream
300
,
310
, and
320
, each comprising packets containing I picture information. FIG.
10
(
c
) is a bitstream (elementary stream) comprising data contained in payloads of the parts of the bitstream
300
,
310
,
320
, . . . .
In the fast forward playback process, the entire bitstream is not supplied to the decoding apparatus but the parts of the bitstream
300
,
310
,
310
, . . . , ar
Nakatani Shintaro
Yasuda Makoto
Pham Chi
Tran Khai
Wenderoth , Lind & Ponack, L.L.P.
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