Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-07-20
2002-07-30
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06426975
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image processing methods, image processing apparatuses, and data recording media and, more particularly, to image processing methods, image processing apparatuses, and data recording media in which, in variable-length coding of frequency components of an interlaced image signal, a sequence of the frequency components is adaptively rearranged, thereby improving coding efficiency.
BACKGROUND OF THE INVENTION
In recent years, discrete cosine transformation (DCT) has been widely utilized in image coding processing. In MPEG as a representative image coding method, an input image signal is divided correspondingly to plural rectangular blocks constituting a single display screen as units of DCT processing, and DCT processing is performed block by block to the blocked image signal.
A specific description is given of image coding in MPEG.
FIG. 26
is a block diagram illustrating a construction of a conventional image processing apparatus which performs the above-mentioned image coding. In
FIG. 26
, reference numeral
200
a
designates a conventional image processing apparatus (image coding apparatus), which performs coding including DCT processing to an image signal. This image coding apparatus
200
a
consists of a blocking unit
102
for dividing an input image signal
101
correspondingly to plural blocks constituting a single display screen to generate an image signal (plural pixel values)
103
corresponding to each block, a DCT unit
104
for performing DCT processing to the image signal (pixel values)
103
to transform the image signal (pixel values)
103
into frequency components (DCT coefficients)
105
, and a quantization unit
106
for quantizing the output
105
of the DCT unit
104
to generate quantized values
107
corresponding to each block. Herein, the DCT unit
104
and the quantization unit
106
constitute an information source coding unit
200
a
1
.
Further, the image coding apparatus
200
a
consists of a scanner
109
for setting the processing order for coding the quantized values
107
, and a variable-length coding unit (hereinafter referred to as a VLC unit)
112
for performing variable-length coding to quantized values
111
to which the processing order has been set, according to the set order, to generate a bit stream
113
corresponding to the image signal of each block.
A description is given of the operation.
Initially, the blocking unit
102
blocks an input image signal
101
correspondingly to rectangular blocks each comprising 8×8 pixels, and outputs an image signal (plural pixel values)
103
corresponding to each block. The DCT unit
104
transforms the image signal (pixel values)
103
into plural frequency components (DCT coefficients)
105
by DCT. The quantization unit
106
converts the DCT coefficients
105
into quantized values
107
by quantization.
Then, the scanner
109
performs rearrangement of the quantized values
107
so as to improve the efficiency of variable-length coding. That is, the scanner
109
sets the processing order for coding. Thereafter, the VLC unit
112
performs variable-length coding to the quantized values which have been rearranged, according to the set order. In addition, run length coding is used in variable-length coding processing. Therefore, when a scan is performed so that coefficients of about the same size are consecutive, the efficiency of variable-length coding is improved.
In coding an interlaced image signal, when correlations between adjacent scan lines are strong, frame DCT processing, i.e., DCT using a frame as a unit, is carried out. When correlations between scan lines in a field are strong, field DCT processing, i.e., DCT using a field as a unit, is carried out.
More specifically, as shown in
FIG. 27
, in frame DCT processing of an interlaced image signal, scan lines of a first field and scan lines of a second field are alternately arranged to form one frame-screen. This frame screen is divided into plural macroblocks each comprising 16×16 pixels. Each macroblock is divided into four subblocks-each comprising 8×8 pixels. Thereby, the image signal is subjected to DCT processing subblock by subblock. Meanwhile, in field DCT processing of an interlaced image signal, Each of macroblocks constituting one frame screen is formed by two first subblocks comprising only scan lines of a first field and two second subblocks comprising only scan lines of a second field. Thereby, the image signal is subjected to DCT processing subblock by subblock.
In MPEG, frame DCT or field DCT is adaptively selected for each macroblock. Accordingly, in order to perform accurate decoding to an input image signal, the blocking unit
102
in the image coding apparatus
200
a
outputs DCT processing information
114
indicating a unit of DCT processing for each macroblock (that is, information indicating whether each macroblock has been subjected to frame DCT or field DCT), together with the blocked image signal. Since a subblock which has been subjected to field DCT (a field DCT block) comprises only odd scan lines or only even scan lines among scan lines constituting one frame screen, a DCT coefficient group corresponding to the field DCT block includes more DCT coefficients indicating that the rate of change of pixel values in a vertical direction of a display screen is higher, as compared with a DCT coefficient group corresponding to a subblock which has been subjected to frame DCT (a field DCT block).
FIG. 28
is a block diagram illustrating a construction of an image decoding apparatus corresponding to the image coding apparatus shown in FIG.
26
. In
FIG. 28
, reference numeral
200
b
designates an image processing apparatus (image decoding apparatus), which decodes the coded image signal
113
which has been coded by the image coding apparatus
200
a.
This image decoding apparatus
200
b
consists of a variable-length decoding unit (hereinafter referred to as a VLD unit)
201
for performing variable-length decoding to the coded image signal
113
, and an inverse scanner
202
for performing an inverse scan to quantized values
111
which are obtained by decoding so that the order of the quantized values
111
is returned to the order before rearrangement in coding. Further, the image decoding apparatus
200
b
consists of an inverse quantization unit
203
for inverse-quantizing quantized values
107
which have been subjected to inverse scanning, to generate DCT coefficients (frequency components)
105
corresponding to a decoding target block to be subjected to decoding, an inverse DCT unit
204
for performing inverse DCT processing to the DCT coefficients
105
to generate an image signal (pixel values)
103
corresponding to the decoding target block, and an inverse blocking unit
205
for inverse-blocking the image signals
103
on the basis of the DCT processing information
114
from the image coding apparatus
200
a,
thereby regenerating an image signal
101
corresponding to one frame screen. Herein, the inverse quantization unit
203
and the inverse DCT unit
204
constitute an information source decoding unit
200
b
1
.
In the image decoding apparatus
200
b,
inverse converting processes corresponding to the respective converting processes in the image coding apparatus
200
a
are carried out to a coded image signal, in the reverse order of the order in coding, thereby accurately decoding the coded image signal.
FIG. 29
is a block diagram illustrating a construction of another conventional image coding apparatus.
In
FIG. 29
, reference numeral
200
c
designates an image processing apparatus (image coding apparatus), which performs intra-frame predictive coding processing comprising generating predicted values of quantized values of a coding target block using information in a frame, and coding difference values between the predicted values and the quantized values of the coding target block.
This image coding apparatus
200
c
includes the image coding apparatus
200
a,
a prediction unit
200
c
2
for generating pred
Boon Choong Seng
Kadono Shinya
Nishi Takahiro
Takahashi Toshiya
Kelley Chris
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Vo Tung
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