Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-06-09
2002-10-01
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06459736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to moving picture decoding, and more particularly to a moving picture decoding apparatus and method for decoding bit stream data of a moving picture encoded by intraframe encoding and interframe encoding.
2. Description of the Prior Art
The MPEG (Moving Picture Experts Group) standard is known as an international standard related to the image compression scheme, the disclosure of which is hereby incorporated by reference. The moving picture encoding/decoding technique consistent with the MPEG standard is one of the essential schemes in the recent multimedia environment. Now, a variety of moving picture encoding/decoding is developed.
The encoding system based on the MPEG standard employs a variable-length code in which the number of bits forming data after encoding is not fixed but varied. That is, the amount of information per picture obtained after encoding is increased or decreased on the basis of the property of picture. With the above in mind, a decoder temporarily stores picture data in a built-in buffer memory after encoding (such picture data is referred to as bit stream) in order to start the decoding process when a given number of pictures (picture planes or sheets) is stored. If the buffer memory overflows or underflows, the decoder will not operate normally. In order to avoid the above problem, it is required to monitor the amount of data which is currently stored in the buffer memory and thus control the amount of the bit stream to be written to the buffer memory and the amount of bit stream to be read therefrom.
The MPEG standard is silent in the method of controlling the buffer memory. Hence, various buffer memory control methods have been proposed.
FIG. 1
is a block diagram of a conventional moving picture decoding apparatus, which is directed to monitoring, per picture, the amount of the bit stream occupying the buffer memory by using a temporary reference. A bit stream input part
12
is located at the front stage of a buffer memory
11
, and a video decoder
13
is provided at the rear stage thereof. The bit stream input part
12
includes a PSC (Picture Start Code) detector
16
and a TR (Temporary Reference) detector
17
. A controller
14
controls the bit stream input part
12
and the video decoder
13
. The controller
14
includes a picture counter
18
, which counts the number of pictures (picture planes).
An operation of the apparatus shown in
FIG. 1
will be given by referring to FIG.
2
.
First, at time t
0
, the controller
14
issues a bit stream request against the bit stream input part
12
in order to store, in the buffer memory
11
, data to be decoded, namely, a bit stream supplied from an external storage medium
15
. In response to receipt of the bit stream request, the bit stream input part
12
starts to read the bit stream from the external storage medium
15
. The bit stream input part
12
extracts a picture start code PSC and a temporary reference TR while reading the bit stream from the external storage medium
15
. The picture start code PSC indicates the beginning of the picture layer. According to the MPEG standard, the moving picture data has a hierarchal structure consisting of six layers. Besides the picture layer, the moving picture data has the block layer, macro block layer, slice layer a GOP (Group Of Picture) layer, and sequence layer. The temporary reference TR is a display sequence number assigned to each picture, and is reset at the beginning of the GOP.
FIG. 3
is a diagram showing the concept of the GOP and the temporary reference TR. Each of the GOPs includes a plurality of pictures. For the sake of simplicity,
FIG. 3
shows each GOP includes four pictures. The temporary reference TR is a serial number which is assigned to each GOP and starts from “0”. The MPEG standard defines an I picture (Intra picture), a P picture (Predictive picture) and a B picture (Bidirectionally predictive picture). Each picture is one of the I, P and B pictures. A GOP header is inserted at the beginning portion of each GOP, and includes a group start code.
It will be noted that the structure shown in
FIG. 3
is a frame structure (non-interlace). A field structure (interlace) is known in which one frame consists of an odd field and an even field to which fields an identical temporary reference is assigned.
If the value of the temporary reference TR differs from that of the temporary reference assigned to the immediately prior picture, the bit stream input part
12
informs the controller
14
of detection of picture (time t
1
shown in FIG.
2
). Then, the bit stream input part
12
writes pictures into the buffer memory
11
.
When the controller
14
is informed of the detection of picture, it counts up an internal picture counter
18
(time t
1
). In the example shown in
FIG. 2
, the count value is changed from “0” to “1”. Subsequently, the controller
14
issues the bit stream request until the picture counter becomes equal to “2”.
When the picture counter becomes equal to “2”, the controller
14
determines that data to be decoded is available in the buffer memory
11
, and stops issuing the bit stream request. Then, the controller
14
issues a decode start instruction (time t
2
). The video decoder
13
, which is in the standby state, receives the decode start instruction, and starts decoding in synchronism with a vertical synchronizing signal VSYNC. At that time, the video decoder
13
sends a picture consumption notification to the controller
14
.
In response to receipt of the picture consumption notification, the controller
14
counts down the picture counter
18
. In the example shown in
FIG. 2
, the count value is changed from “2” to “1”. When the picture counter
18
becomes equal to “1”, the controller
14
issues the bit stream request again (time t
3
).
The above sequence is repeatedly carried out during the decode process, the controller
14
issues the bit stream request against the bit stream input part
12
and issues the decode start instruction against the video decoder
13
so that the count value of the picture counter
18
is always “2”.
The above sequence does not cause any problem in the normal decoding. However, a problem occurs in a decoding other than the normal decoding, such as a quick decoding.
Let us consider a case where only I pictures are decoded in the quick decoding. The bit stream input part
12
discards the P and B pictures and picks up only the I pictures. The above selecting operation refers to the value of a PCT (Picture Code Type), which will be described later with reference to FIG.
5
. The PCT indicates whether the encoded data is obtained by using the intraframe encoding or the interface encoding. The I picture (intraframe encoding) is indicated when PCT=1. The P and B pictures are respectively indicated when the PCT is equal to 2 and 3, respectively.
If there is a bit stream in which a group includes only one I picture, the bit stream input part
12
cannot issue the picture detection notification. This is because the value of the temporary reference TR is reset by the I picture located at the beginning of the group and is always equal to “0”. Hence, the bit stream input part
12
does not detect a change of the value of the temporary reference TR. Hence, the bit stream input part
12
does not decode a picture to be decoded, and writes the corresponding bit stream into the buffer memory
11
. Hence, the quick decoding does not function.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a moving picture decoding apparatus and method in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a moving picture decoding apparatus and method capable of quick-decoding any bit stream.
The above objects of the present invention are achieved by a moving picture decoding apparatus comprising: an input part which provides a picture tag to a bit stream which has been subjected to intraframe or interface encod
Inagaki Hirohiko
Ishizuka Masanori
Kono Tadayoshi
Ohta Mitsuhiko
Yamashita Koichi
Fujitsu Limited
Le Vu
Staas & Halsey , LLP
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