Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1996-12-04
2002-04-30
Lee, Young (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240140
Reexamination Certificate
active
06381275
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image coding apparatus and an image decoding apparatus for use with a system which performs high efficiency coding or decoding of moving pictures to perform efficient transmission or storage of images, and more particularly to an image coding apparatus and an image decoding apparatus which can be applied to processing of, for example, a digital broadcasting system which is performed using a satellite or a ground wave or cable communication network, a digital video disk, a mobile video phone, a PHS video phone or a data base for images.
2. Description of the Prior Art
As a representative one of conventional high efficiency coding systems, the MPEG2 is known which is an international standard system recommended by the ISO/IEC/JTC1/SC29/WG11. For example, “Image Information Engineering and Broadcasting Techniques”, Journal of the Television Engineering Society of Japan, April, 1995 explains the MPEG as a theme of special editing. A coding system of the MPEG2 is disclosed in “
3-2
Video Compression” of the same document, pp. 29-60.
The coding system of the MPEG2 is described below.
FIG. 31
is a block diagram showing a basic construction of an ordinary encoder of the MPEG2, and
FIG. 32
is a block diagram showing a basic construction of an MPEG2 decoder. Referring to
FIGS. 31 and 32
, reference numeral
1
denotes a frame re-arranging unit,
2
a subtracting unit, reference characters
3
a
and
3
b
denote each an inter(interframe)/intra(intraframe) switching selector, reference numeral
4
denotes a converting unit,
5
a quantizing unit,
6
a reverse quantizing unit,
7
a reverse converting unit,
8
an adder,
9
a first frame memory,
10
a second frame memory,
11
a forward direction motion compensating unit,
12
a bidirection motion compensating unit,
13
a backward direction motion compensating unit,
151
a motion estimating unit,
16
a coding control unit,
17
a variable length coding unit, and
18
a buffer.
Further, reference numeral
100
denotes input image data in the form of digital data,
101
re-arranged input image data,
102
a predictive error image,
103
an original input image or predictive error image,
104
a conversion coefficient,
105
a quantization coefficient,
106
a reverse quantized conversion coefficient,
107
reversed converted image data,
108
a locally decoded image,
109
a reference image from the first frame memory,
110
a reference image from the second frame memory,
111
a forward direction motion predicted image,
112
a bidirection motion predicted image,
113
a backward direction motion predicted image,
115
a determined predicted image,
117
a control signal to the selector,
118
a control signal to the converting unit
4
,
119
an adaptive quantization value,
120
a variable length coder,
121
a bit stream,
123
a motion vector,
124
a reference image, and
125
an intra/inter switching signal.
Operation of the conventional image encoder is described below with reference to FIG.
31
.
First, an input image signal
100
in the form of a digital signal is inputted to the frame re-arranging unit
1
, by which picture frames to be coded are re-arranged.
FIG. 33
illustrates such re-arrangement. Referring to
FIG. 33
, reference character I denotes an intra (intraframe) coded picture, P an interframe coded picture, and B a bidirectional predictive coded picture. It is to be noted that reference numerals 1 to 10 represent an order in time in which they are displayed.
The first frame is first coded as an I picture, and then the fourth frame is coded as a P picture, whereupon the already coded I picture is used as a reference frame for prediction.
Then, the second frame is coded as a B picture. Thereupon, the I picture of the first frame and the P picture of the fourth frame coded already are used as reference frames for the prediction. In
FIG. 33
, each arrow mark represents a direction in which prediction is performed.
Thereafter, coding is performed in the construction of I, B, B, P, B, B, P, . . . by similar processing. Accordingly, the action of the frame re-arranging unit
1
is to re-arrange the input image signal
100
, in which the picture frames are arranged in order of time, so that they appear in order of coding in order to allow the processing described above.
Subsequently, since predictive coding is not performed for the I picture mentioned above, when the re-arranged image
101
is inputted as it is to the selector
3
a,
it is transmitted as a selector output
103
to the converting unit
4
. On the other hand, for predictive coding for the P picture or the B picture mentioned above, the re-arranged image
101
is subtracted from a predicted image
115
by the subtracting unit
2
, and a predictive error image
102
is transmitted as the selector output
103
to the converting unit
4
.
Then, the selector output
103
is inputted to the converting unit
4
, and a conversion coefficient
104
is outputted from the converting unit
4
. The conversion coefficient
104
passes the quantizing unit
5
, and a quantization coefficient
105
is obtained from the quantizing unit
5
. The quantization coefficient
105
is coded into a variable length code by the variable length coding unit
17
, and a variable length coded word
120
is outputted from the variable length coding unit
17
.
The quantization coefficient
105
is, on the other hand, inputted to the reverse quantizing unit
6
, and a quantization coefficient
106
is outputted from the reverse quantizing unit
6
.
Further, the quantization coefficient
106
is reverse converted back to an image level by the reverse converting unit
7
, and image data
107
is outputted from the reverse converting unit
7
. The image data
107
is, where it is data of the I picture, added to a predicted image
116
selected by the adding unit
8
, and a locally decoded image
108
is outputted from the adding unit
8
.
It is to be noted that the locally decoded image
108
is written as it is into the first frame memory
9
when it is an I picture, but, when it is a P picture, it is written into the second frame memory
10
.
On the other hand, when the locally decoded image
108
is a B picture, it is written into neither the first frame memory
9
nor the second frame memory
10
.
Thereafter, when the locally decoded image
108
is a P picture, since it is used only for forward direction prediction, a reference image
124
in the first frame memory
9
is read out, and motion prediction is performed for each macroblock (basic unit for processing of 16 pixels×16 lines) by the motion estimating unit
151
. The motion estimating unit
151
thus selects one of the macroblocks which has a value nearest to that of the current macroblock as a predicted image, and simultaneously outputs a motion vector
123
therefrom.
The motion vector
123
is inputted to the motion compensating units
11
,
12
and
13
surrounded by a dotted line in
FIG. 31
, and motion predictive pictures are outputted from the motion compensating units
11
,
12
and
13
.
In this instance, the forward direction motion compensating unit
11
produces a forward direction motion predicted image
111
using a reference image
109
from the first frame memory
9
and outputs a thus determined predicted image
115
.
Further, as described hereinabove, the locally decoded images
108
of all macroblocks in a P picture are written into the second frame memory. However, even with the P picture mentioned above, when the macroblocks thereof are intraframe (intra) coded, the frame re-arranged image
101
is outputted directly as the selector output.
Meanwhile, for a B picture, the procedure of coding processing is similar to that for a P picture described above, but different from the processing for a P picture, in that two reference frames are used for prediction.
The motion estimating unit
151
performs forward direction prediction using the reference image
109
from the first frame memory
9
, backward direction predic
Asai Kohtaro
Fukuhara Takahiro
Murakami Tokumichi
Sekiguchi Shun-ichi
Lee Young
Mitsubishi Denki & Kabushiki Kaisha
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