Coded data generation or conversion – Digital code to digital code converters – To or from particular bit symbol
Reexamination Certificate
1999-03-22
2001-08-07
Young, Brian (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from particular bit symbol
C375S240000, C348S384100
Reexamination Certificate
active
06271774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a picture data processor, picture data decoder and picture data encoder, and methods thereof, and more particularly, is preferably applicable to the case of decoding and reencoding picture data encoded by the moving picture experts group (MPEG) standard.
2. Description of the Related Art
In a picture data encoder for encoding a motion picture based on, for example, the moving picture experts group (MPEG) standard, encoding is performed with, for example, fifteen frames of motion picture data as one processing unit called a group of pictures (GOP).
In one GOP, there are coding types for each frame, called I-picture (intra-picture: intra-frame coded picture), P-picture (predictive-picture: inter-frame forward direction predictive-encoded picture) and B-picture (bidirectional predictive-picture: bidirectionally predictive-coded picture).
Specifically, as shown in
FIG. 1
, the I-picture (picture IO) is to keep independence of the GOP, and is encoded in the picture. The P-pictures (pictures P
3
, P
6
) are predictive-encoded in the forward direction from the I-picture or P-picture. In this connection, the I-picture and P-picture are encoded in the same sequence as an original picture.
The B-pictures (pictures B
1
, B
2
, B
4
, B
5
) are bidirectionally predictive-encoded from the I-picture or P-picture. Accordingly, when decoding picture data compressively-encoded, the I-picture is solely decoded, but the P-picture and B-picture its picture data are not decoded solely.
FIG. 2A
shows the input order of a motion picture signal to an encoder (that is, the displaying order of the motion picture signal). The first frame picture signal (picture IO) is a picture signal before being encoded as I-picture, and the following second frame picture signal (picture B
1
) is a picture signal before being encoded as B-picture. In this connection, a number added to each picture type (I, P, B) represents the displaying order.
The motion picture signal successively inputted to the encoder in this manner is encoded according to each picture type. In this case, since the B-pictures (pictures B
1
and B
2
) are generated referring to the I-picture (picture IO) and P-picture (picture P
3
), the B-pictures (pictures B
1
and B
2
) are stored in a frame memory until the P-picture (picture P
3
) to be a reference is encoded.
As the above, the encoder needs frame memories as many as the B-pictures between the I-picture (or P-picture) and P-picture. In the case of
FIGS. 2A
to
2
D, there is a space of three pictures between the I-picture (or P-picture) and P-picture. If representing this as M=3, the number of pieces of B-pictures between the I-picture (or P-picture) and P-picture becomes M−1.
Furthermore, if encoding for each picture type is performed in the encoder, each picture is to be outputted in a sequence shown in FIG.
2
B. In this case, since the B-pictures (pictures B
1
and B
2
) are temporarily stored in the frame memory before being encoded and the P-picture (picture P
3
) is previously encoded, coded data (bit stream) is outputted at timing delayed for three frames from the picture IO to the picture P
3
of the input picture signal (
FIG. 2A
) from the input of the picture signal.
Therefore, in the encoder, the inputted motion picture signal is outputted in the state where its frame sequence (the displaying order) has been rearranged in order of encoding by that encoding processing.
Thus coded bit stream (
FIG. 2B
) is inputted to a decoder through a prescribed transmission line and decoded. In this case, as shown in
FIG. 2C
, pictures are inputted in order of pictures outputted from the encoder as described above with reference to FIG.
2
B.
In the decoder, the inputted bit stream is rearranged in order of display to obtain a motion picture signal shown in
FIG. 2D
, and outputs this as a decoded picture signal. In this case, in the decoder, since the inputted bit stream (
FIG. 2C
) is not in order of display, a process to rearrange the inputted bit stream in order of display is necessary. Accordingly, in the decoder, a delay time for one frame is generated after the bit stream was inputted until this is outputted as the decoded picture signal.
By the way, when changing the bit rate of a bit stream once encoded, or the like, it is needed to temporarily decode the encoded bit stream and reencode the decoded picture signal at a different bit rate. As a method of reencoding thus decoded picture signal, a decoding and encoding apparatus
1
as shown in
FIG. 3
can be considered.
Referring to
FIG. 3
, the decoding and encoding apparatus
1
temporarily decodes an encoded bit stream D
1
with a decoder
2
, and reencodes a decoded picture signal D
10
thus decoded with an encoder
20
, to obtain a bit stream D
34
.
As shown in
FIG. 4
, this decoder
2
inputs the inputted bit stream D
1
to a variable-length decoding part
4
via a buffer
3
. The variable-length decoding part
4
performs variable-length decoding on the bit stream D
1
and supplies this to an inverse quantizing part
5
. The inverse quantizing part
5
performs inverse quantizing on the output of the variable-length decoding part
4
to restore a discrete cosine transform (DCT) coefficient sequence D
5
. This is subjected to inverse DCT processing in an inverse DCT part
6
. Thus, difference data according to the picture type is outputted from the inverse DCT part
6
to an arithmetic part
7
.
Here, when decoding the I-picture first inputted as the bit stream D
1
, since the I-picture is data intra-frame-encoded, picture data for one frame is outputted from the inverse DCT part
6
. This picture data is supplied to the following picture sequence rearranging part
10
as decoded picture data D
7
as well as being stored in a frame memory
8
as reference picture data.
A motion compensating part
9
performs motion compensating on the reference picture data stored in the frame memory
8
based on motion vector information (not shown in figure) transmitted from the encoder along with the bit stream D
1
, and supplies this to the arithmetic part
7
as predictive picture data D
9
.
The arithmetic part
7
adds the difference data D
6
outputted from the inverse DCT part
6
to the predictive picture data D
9
, and obtaining the decoded picture data D
7
of a new frame (picture). This decoded picture data D
7
is supplied to the picture sequence rearranging part
10
, and at the same time, it is stored in the frame memory
8
as reference picture data to be a reference picture for the following frame (picture).
In this connection, when the bit stream D
1
shown in
FIG. 5A
is inputted to the decoder
2
, the picture P
3
is restored with the picture IO previously-decoded as a reference picture, and the pictures B
1
and B
2
are restored with the pictures IO and P
3
previously-decoded as reference pictures.
Thus, each of pictures forming the bit stream D
1
is decoded and then rearranged in order of display in the picture sequence rearranging part
10
, so that the decoded picture signal D
10
shown in
FIG. 5B
can be obtained. This decoded picture signal D
10
is outputted from the picture sequence rearranging part
10
of the decoder
2
, and supplied to the encoder
20
(FIG.
3
).
In this connection, in the variable-length decoding part
4
of the decoder
2
, the picture type (I-picture, P-picture, B-picture) of each of the pictures forming the inputted bit stream D
1
is read out from header information corresponding to each picture, and this is supplied to the encoder
20
(
FIG. 3
) as picture coding type information D
40
. The encoder
20
encodes the decoded picture signal D
10
into the same picture type as the picture type encoded in the bit stream D
1
based on the picture coding type information D
40
.
FIG. 6
shows the configuration of the encoder
20
. The decoded picture signal D
10
outputted from the decoder
2
(
FIG. 4
) is stored in a frame memory
21
of the encoder
20
. A motion predicting part
22
detects mo
Frommer William S.
Frommer Lawrence & Haug LLP.
Nguyen John
Simon Darren M.
Sony Corporation
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