U.S. patent application number 12/491829 was filed with the patent office on 2009-10-15 for video encoding/decoding method and apparatus.
Invention is credited to Takeshi Chujoh, Yoshihiro Kikuchi, Shinichiro Koto.
Application Number | 20090257495 12/491829 |
Document ID | / |
Family ID | 29253594 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090257495 |
Kind Code |
A1 |
Chujoh; Takeshi ; et
al. |
October 15, 2009 |
VIDEO ENCODING/DECODING METHOD AND APPARATUS
Abstract
A video encoding method comprises selecting one combination, for
each block of an input video signal, from a plurality of
combinations each including a predictive parameter and at least one
reference picture number determined in advance for the reference
picture, generating a prediction picture signal in accordance with
the reference picture number and predictive parameter of the
selected combination, generating a predictive error signal
representing an error between the input video signal and the
prediction picture signal, and encoding the predictive error
signal, information of the motion vector, and index information
indicating the selected combination.
Inventors: |
Chujoh; Takeshi; (Tokyo,
JP) ; Koto; Shinichiro; (Machida-shi, JP) ;
Kikuchi; Yoshihiro; (Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
29253594 |
Appl. No.: |
12/491829 |
Filed: |
June 25, 2009 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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12323930 |
Nov 26, 2008 |
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12491829 |
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11687923 |
Mar 19, 2007 |
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12323930 |
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10754535 |
Jan 12, 2004 |
7450643 |
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11687923 |
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PCT/JP03/04992 |
Apr 18, 2003 |
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10754535 |
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Current U.S.
Class: |
375/240.12 ;
375/E7.243 |
Current CPC
Class: |
H04N 19/107 20141101;
H04N 19/176 20141101; H04N 19/51 20141101; H04N 19/423 20141101;
H04N 19/61 20141101; H04N 19/174 20141101; H04N 19/105 20141101;
H04N 19/126 20141101; H04N 19/573 20141101; H04N 19/70 20141101;
H04N 19/46 20141101; H04N 19/103 20141101; H04N 19/139
20141101 |
Class at
Publication: |
375/240.12 ;
375/E07.243 |
International
Class: |
H04N 7/32 20060101
H04N007/32 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2002 |
JP |
2002-116718 |
Nov 22, 2002 |
JP |
2002-340042 |
Claims
1. A prediction image generation method for generating a prediction
image by decoding encoded data obtained by subjecting a video image
comprising a luminance and two color differences to prediction
encoding, comprising: a step of receiving an input of encoded data
obtained by encoding, for one or more to-be-decoded blocks, a
plurality of combinations comprising (A) a weighting factor every
luminance and two color differences, (B) an offset every luminance
and two color differences and a flag indicating presence or
non-presence of the weighting factor and the offset for the
luminance and encoding, for a to-be-decoded block, an index
indicating (1) information of a motion vector and (2) a combination
of the plurality of combinations; a step of deriving, for the
to-be-decoded block, the weighting factor and the offset from the
index and the plurality of combinations; and a step of generating a
prediction image by multiplying a reference image by the weighting
factor and adding the offset, based on the motion vector.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of and claims the benefit of priority
under 35 U.S.C. .sctn.120 from U.S. application Ser. No.
12/323,930, filed on Nov. 26, 2008, which is a divisional U.S.
application Ser. No. 11/687,923, filed on Mar. 19, 2007, which is a
divisional of U.S. application Ser. No. 10/754,535, filed on Jan.
12, 2004, which is a continuation of International Application No.
PCT/JP03/04992, filed Apr. 18, 2003, which was not published under
PCT Article 21(2) in English.
[0002] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No.
2002-116718, filed Apr. 18, 2002; and No. 2002-340042, filed Nov.
22, 2002, the entire contents of both of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a video encoding/decoding
method and apparatus which encode/decode a fade video and
dissolving video, in particular, at high efficiency.
[0005] 2. Description of the Related Art
[0006] Motion compensation predictive inter-frame encoding is used
as one of encoding modes in a video encoding standard scheme such
as ITU-TH.261, H.263, ISO/IEC MPEG-2, or MPEG-4. As a predictive
model in motion compensation predictive inter-frame encoding, a
model that exhibits the highest predictive efficiency when no
change in brightness occurs in the time direction is used. In the
case of a fade video which changes in the brightness of pictures,
there is no method known up to now which makes a proper prediction
against a change in the brightness of pictures when, for example, a
normal picture fades in from a black picture. In order to maintain
picture quality in a fade video as well, therefore, a large number
of bits are required.
[0007] In order to solve this problem, for example, in Japanese
Patent No. 3166716, "Fade Countermeasure Video Encoder and Encoding
Method", a fade video part is detected to change the allocation of
the number of bits. More specifically, in the case of a fadeout
video, a large number of bits are allocated to the start part of
fadeout that changes in luminance. In general, the last part of
fadeout becomes a monochrome picture, and hence can be easily
encoded. For this reason, the number of bits allocated to this part
is reduced. This makes it possible to improve the overall picture
quality without excessively increasing the total number of
bits.
[0008] In Japanese Patent No. 2938412, "Video Luminance Change
Compensation Method, Video Encoding Apparatus, Video Decoding
Apparatus, Recording Medium on Which Video Encoding or Decoding
Program Is Recorded, and Recording Medium on Which Encoded Data of
Video Is Recorded", there is proposed an encoding scheme of
properly coping with a fade video by compensating for a reference
picture in accordance with two parameters, i.e., a luminance change
amount and contrast change amount.
[0009] In Thomas Wiegand and Berand Girod, "Multi-frame
motion-compensated prediction for video transmission", Kluwer
Academic Publishers 2001, an encoding scheme based on a plurality
of frame buffers is proposed. In this scheme, an attempt has been
made to improve the predictive efficiency by selectively generating
a prediction picture from a plurality of reference frames held in
the frame buffers.
[0010] According to the conventional techniques, in order to encode
a fade video or dissolving video while maintaining high picture
quality, a large number of bits are required. Therefore, an
improvement in encoding efficiency cannot be expected.
BRIEF SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a video
encoding/decoding method and apparatus which can encode a video
which changes in luminance over time, e.g., a fade video or
dissolving video, in particular, at high efficiency.
[0012] According to a first aspect of the present invention, there
is provided a video encoding method of subjecting an input videos
signal to motion compensation predictive encoding by using a
reference picture signal representing at least one reference
picture and a motion vector between the input video signal and the
reference picture signal, comprising: selecting one combination,
for each block of the input video signal, from a plurality of
combinations each including a predictive parameter and at least one
reference picture number determined in advance for the reference
picture; generating a prediction picture signal in accordance with
the reference picture number and predictive parameter of the
selected combination; generating a predictive error signal
representing an error between the input video signal and the
prediction picture signal; and encoding the predictive error
signal, information of the motion vector, and index information
indicating the selected combination.
[0013] According to a second aspect of the present invention, there
is provided a video decoding method comprising: decoding encoded
data including a predictive error signal representing an error in a
prediction picture signal with respect to a video signal, motion
vector information, and index information indicating a combination
of at least one reference picture number and a predictive
parameter; generating a prediction picture signal in accordance
with the reference picture number and predictive parameter of the
combination indicated by the decoded index information; and
generating a reproduction video signal by using the predictive
error signal and the prediction picture signal.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] FIG. 1 is a block diagram showing the arrangement of a video
encoding apparatus according to the first embodiment of the present
invention;
[0015] FIG. 2 is a block diagram showing the detailed arrangement
of a frame memory/prediction picture generator in FIG. 1;
[0016] FIG. 3 is a view showing an example of a table of
combinations of reference frame numbers and predictive parameters,
which is used in the first embodiment;
[0017] FIG. 4 is a flow chart showing an example of a sequence for
selecting a predictive scheme (a combination of a reference frame
number and a predictive parameter) for each macroblock and
determining an encoding mode in the first embodiment;
[0018] FIG. 5 is a block diagram showing the arrangement of a video
decoding apparatus according to the first embodiment;
[0019] FIG. 6 is a block diagram showing the detailed arrangement
of the frame memory/prediction picture generator in FIG. 5;
[0020] FIG. 7 is a view showing an example of a table of
combinations of predictive parameters in a case wherein the number
of reference frames is one and a reference frame number is sent as
mode information according to the second embodiment of the present
invention;
[0021] FIG. 8 is a view showing an example of a table of
combinations of predictive parameters in a case wherein the number
of reference frames is two and a reference frame number is sent as
mode information according to the second embodiment;
[0022] FIG. 9 is a view showing an example of a table of
combinations of reference picture numbers and predictive parameters
in a case wherein the number of reference frame is one according to
the third embodiment of the present invention;
[0023] FIG. 10 is a view showing an example of a table for only
luminance signals according to the third embodiment;
[0024] FIG. 11 is a view showing an example of a syntax for each
block when index information is to be encoded;
[0025] FIG. 12 is a view showing a specific example of an encoded
bit stream when a prediction picture is to be generated by using
one reference picture;
[0026] FIG. 13 is a view showing a specific example of an encoded
bit stream when a prediction picture is to be generated by using
two reference pictures;
[0027] FIG. 14 is a view showing an example of a table of reference
frame numbers, reference field numbers, and predictive parameters
when information to be encoded is a top field according to the
fourth embodiment of the present invention; and
[0028] FIG. 15 is a view showing an example of a table of reference
frame numbers, reference field numbers, and predictive parameters
when information to be encoded is a bottom field according to the
fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The embodiments of the present invention will be described
below with reference to the several views of the accompanying
drawing.
First Embodiment
About Encoding Side
[0030] FIG. 1 shows the arrangement of a video encoding apparatus
according to the first embodiment of the present invention. A video
signal 100 is input to the video encoding apparatus, for example,
on a frame basis. The video signal 100 is input to a subtracter
101. The subtracter 101 calculates the difference between the video
signal 100 and a prediction picture signal 212 to generate a
predictive error signal. A mode selection switch 102 selects either
the predictive error signal or the video signal 100. An orthogonal
transformer 103 subjects the selected signal to an orthogonal
transformation, e.g., a discrete cosine transform (DCT). The
orthogonal transformer 103 generates orthogonal transformation
coefficient information, e.g., DCT coefficient information. The
orthogonal transformation coefficient information is quantized by a
quantizer 104 and branched into two paths. One quantization
orthogonal transformation coefficient information 210 branched into
two paths is guided to a variable-length encoder 111.
[0031] The other quantization orthogonal transformation coefficient
information 210 branched into the two paths is sequentially
subjected to processing reverse to that in the quantizer 104 and
orthogonal transformer 103 by a dequantizer or inverse quantizer
105 and inverse orthogonal transformer 106 to be reconstructed into
a predictive error signal. Thereafter, an adder 107 adds the
reconstructed predictive error signal to the prediction picture
signal 212 input through a switch 109 to generate a local decoded
video signal 211. The local decoded video signal 211 is input to a
frame memory/prediction picture generator 108.
[0032] The frame memory/prediction picture generator 108 selects
one of a plurality of combinations of prepared reference frame
numbers and predictive parameters. The linear sum of the video
signal (local decoded video signal 211) of the reference frame
indicated by the reference frame number of the selected combination
is calculated in accordance with the predictive parameter of the
selected combination, and the resultant signal is added to an
offset based on the predictive parameter. With this operation, in
this case, a reference picture signal is generated on a frame
basis. Subsequently, the frame memory/prediction picture generator
108 motion-compensates for the reference picture signal by using a
motion vector to generate the prediction picture signal 212.
[0033] In this process the frame memory/prediction picture
generator 108 generates motion vector information 214 and index
information 215 indicating a selected combination of a reference
frame number and a predictive parameter, and sends information
necessary for selection of an encoding mode to a mode selector 110.
The motion vector information 214 and index information 215 are
input to a variable-length encoder 111. The frame memory/prediction
picture generator 108 will be described in detail later.
[0034] The mode selector 110 selects an encoding mode on a
macroblock basis on the basis of predictive information P from the
frame memory/prediction picture generator 108, i.e., selects either
the intraframe encoding mode or the motion compensated predictive
interframe encoding mode, and outputs switch control signals M and
S.
[0035] In the intraframe encoding mode, the switches 102 and 112
are switched to the A side by the switch control signals M and S,
and the input video signal 100 is input to the orthogonal
transformer 103. In the interframe encoding mode, the switches 102
and 112 are switched to the B side by the switch control signals M
and S. As a consequence, the predictive error signal from the
subtracter 101 is input to the orthogonal transformer 103, and the
prediction picture signal 212 from the frame memory/prediction
picture generator 108 is input to the adder 107. Mode information
213 is output from the mode selector 110 and input to the
variable-length encoder 111.
[0036] The variable-length encoder 111 subjects the quantization
orthogonal transformation coefficient information 210, mode
information 213, motion vector information 214, and index
information 215 to variable-length encoding. The variable-length
codes generated by this operation are multiplexed by a multiplier
114. The resultant data is then smoothed by an output buffer 115.
Encoded data 116 output from the output buffer 115 is sent out to a
transmission system or storage system (not shown).
[0037] An encoding controller 113 controls an encoding unit 112.
More specifically, the encoding controller 113 monitors the buffer
amount of the output buffer 115, and controls encoding parameters
such as the quantization step size of the quantizer 104 to make the
buffer amount constant.
(About Frame Memory/Prediction Picture Generator 108)
[0038] FIG. 2 shows the detailed arrangement of the frame
memory/prediction picture generator 108 in FIG. 1. Referring to
FIG. 2, the local decoded video signal 211 input from the adder 107
in FIG. 1 is stored in a frame memory set 202 under the control of
a memory controller 201. The frame memory set 202 has a plurality
of (N) frame memories FM1 to FMN for temporarily holding the local
decoded video signal 211 as a reference frame.
[0039] In a predictive parameter controller 203 is prepared a
plurality of combinations of reference frame numbers and predictive
parameters in advance as a table. The predictive parameter
controller 203 selects, on the basis of the video signal 100, a
combination of the reference frame number of a reference frame and
a predictive parameter that is used to generate the prediction
picture signal 212, and outputs the index information 215
indicating the selected combination.
[0040] A multi-frame motion evaluator 204 generates a reference
picture signal in accordance with the combination of the reference
frame number and the index information selected by the predictive
parameter controller 203. The multi-frame motion evaluator 204
evaluates the motion amount and predictive error from this
reference picture signal and input video signal 100, and outputs
the motion vector information 214 that minimizes the predictive
error. A multi-frame motion compensator 205 carries out
motion-compensation for each block using a reference picture signal
selected by the multi-frame motion evaluator 204 in accordance with
the motion vector to generate the prediction picture signal
212.
[0041] The memory controller 201 sets a reference frame number to a
local decoded video signal for each frame, and stores each frame in
one of the frame memories FM1 to FMN of the frame memory set 202.
For example, the respective frames are sequentially numbered from
the frame nearest to the input picture. The same reference frame
number may be set for different frames. In this case, for example,
different predictive parameters are used. A frame near to the input
picture is selected from the frame memories FM1 to FMN and sent to
the predictive parameter controller 203.
(About Table of Combinations of Reference Frame Numbers and
Prediction Parameters)
[0042] FIG. 3 shows an example of the table of combinations of
reference frame numbers and predictive parameters, which is
prepared in the predictive parameter controller 203. "Index"
corresponds to prediction pictures that can be selected for each
block. In this case, there are eight types of prediction pictures.
A reference frame number n is the number of a local decoded video
used as a reference frame, and in this case, indicates the number
of a local decoded video corresponding to n past frames.
[0043] When the prediction picture signal 212 is generated by using
the picture signals of a plurality of reference frames stored in
the frame memory set 202, a plurality of reference frame numbers
are designated, and (the number of reference frames+1) coefficients
are designated as predictive parameters for each of a luminance
signal (Y) and color difference signals (Cb and Cr). In this case,
as indicated by equations (1) to (3), n assumes the number of
reference frames, n+1 predictive parameters Di (i=1, . . . , n+1)
are prepared for the luminance signal Y; n+1 predictive parameters
Ei (i=1, . . . , n+1), for the color difference signal Cb; and n+1
predictive parameters Fi (i=1, . . . , n+1), for the color
difference signal Cr:
Y t = i = 1 n D i Y t - i + D n + 1 ( 1 ) Cb t = i = 1 n E i Cb t -
i + E n + 1 ( 2 ) Cr t = i = 1 n F i Cr t - i + F n + 1 ( 3 )
##EQU00001##
[0044] This operation will be described in more detail with
reference to FIG. 3. Referring to FIG. 3, the last numeral of each
predictive parameter represents an offset, and the first numeral of
each predictive parameter represents a weighting factor (predictive
coefficient). For index 0, the number of reference frames is given
by n=2, the reference frame number is 1, and predictive parameters
are 1 and 0 for each of the luminance signal Y and color difference
signals Cr and Cb. What the predictive parameters are 1 and 0 as in
this case indicates that a local decoded video signal corresponding
to the reference frame number "1" is multiplied by 1 and added to
offset 0. In other words, the local decoded video signal
corresponding to the reference frame number 1 becomes a reference
picture signal without any change.
[0045] For index 1, two reference frames as local decoded video
signals corresponding to the reference frame numbers 1 and 2 are
used. In accordance with predictive parameters 2, -1, and 0 for the
luminance signal Y, the local decoded video signal corresponding to
the reference frame number 1 is doubled, and the local decoded
video signal corresponding to the reference frame number 2 is
subtracted from the resultant signal. Offset 0 is then added to the
resultant signal. That is, extrapolation prediction is performed
from the local decoded video signals of two frames to generate a
reference picture signal. For the color difference signals Cr and
Cb, since predictive parameters are 1, 0, and 0, the local decoded
video signal corresponding to the reference frame number 1 is used
as a reference picture signal without any change. This predictive
scheme corresponding to index 1 is especially effective for a
dissolving video.
[0046] For index 2, in accordance with predictive parameters 5/4
and 16, the local decoded video signal corresponding to the
reference frame number 1 is multiplied by 5/4 and added with offset
16. For the color difference signals Cr and Cb, since the
predictive parameter is 1, the color difference signals Cr and Cb
become reference picture signals without any change. This
predictive scheme is especially effective for a fade-in video from
a black frame.
[0047] In this manner, reference picture signals can be selected on
the basis of a plurality of predictive schemes with different
combinations of the numbers of reference frames to be used and
predictive parameters. This makes it possible for this embodiment
to properly cope with a fade video and dissolving video that have
suffered deterioration in picture quality due to the absence of a
proper predictive scheme.
(About Sequence for Selecting Prediction Scheme and Determining
Encoding Mode)
[0048] An example of a specific sequence for selecting a predictive
scheme (a combination of a reference frame numbers and a predictive
parameter) for each macroblock and determining an encoding mode in
this embodiment will be described next with reference to FIG.
4.
[0049] First of all, a maximum assumable value is set to variable
min_D (step S101). LOOP1 (step S102) indicates a repetition for the
selection of a predictive scheme in interframe encoding, and
variable represents the value of "index" in FIG. 3. In this case,
in order to obtain an optimal motion vector for each predictive
scheme, an evaluation value D of each index (each combination of a
reference frame number and a predictive parameter) is calculated
from the number of bits associated with motion vector information
214 (the number of bits of a variable-length code output from the
variable-length encoder 111 in correspondence with the motion
vector information 214) and a predictive error absolute value sum,
and a motion vector that minimizes the evaluation value D is
selected (step S103). The evaluation value D is compared with min_D
(step S104). If the evaluation value D is smaller than min_D, the
evaluation value D is set to min_D, and index i is assigned to
min_i (step S105).
[0050] An evaluation value D for intraframe encoding is then
calculated (step S106). The evaluation value D is compared with
min_D (step S107). If this comparison indicates that min_D is
smaller than the evaluation value D, mode MODE is determined as
interframe encoding, and min_i is assigned to index information
INDEX (step S108). If the evaluation value D is smaller, mode MODE
is determined as intraframe encoding (step S109). In this case, the
evaluation value D is set as the estimated value of the number of
bits with the same quantization step size.
(About Decoding Side)
[0051] A video decoding apparatus corresponding to the video
encoding apparatus shown in FIG. 1 will be described next. FIG. 5
shows the arrangement of the video decoding apparatus according to
this embodiment. Encoded data 300 sent out from the video encoding
apparatus show in FIG. 1 and sent through a transmission system or
storage system is temporarily stored in an input buffer 301 and
demultiplexed by a demultiplexer 302 for each frame on the basis of
a syntax. The resultant data is input to a variable-length decoder
303. The variable-length decoder 303 decodes the variable-length
code of each syntax of the encoded data 300 to reproduce a
quantization orthogonal transformation coefficient, mode
information 413, motion vector information 414, and index
information 415.
[0052] Of the reproduced information, the quantization orthogonal
transformation coefficient is dequantized by a dequantizer 304 and
inversely orthogonal-transformed by an inverse orthogonal
transformer 305. If the mode information 413 indicates the
intraframe encoding mode, a reproduction video signal is output
from the inverse orthogonal transformer 305. This signal is then
output as a reproduction video signal 310 through an adder 306.
[0053] If the mode information 413 indicates the interframe
encoding mode, a predictive error signal is output from the inverse
orthogonal transformer 305, and a mode selection switch 309 is
turned on. The prediction picture signal 412 output from a frame
memory/prediction picture generator 308 is added to the predictive
error signal by the adder 306. As a consequence, the reproduction
video signal 310 is output. The reproduction video signal 310 is
stored as a reference picture signal in the frame memory/prediction
picture generator 308.
[0054] The mode information 413, motion vector information 414, and
index information 415 are input to the frame memory/prediction
picture generator 308. The mode information 413 is also input to
the mode selection switch 309. In the intraframe encoding mode, the
mode selection switch 309 is turned off. In the interframe encoding
mode, the switch is turned on.
[0055] Like the frame memory/prediction picture generator 108 on
the encoding side in FIG. 1, the frame memory/prediction picture
generator 308 includes a plurality of prepared combinations of
reference frame numbers and predictive parameters as a table, and
selects one combination indicated by the index information 415 from
the table. The linear sum of the video signal (reproduction video
signal 210) of the reference frame indicated by the reference frame
number of the selected combination is calculated in accordance with
the predictive parameter of the selected combination, and an offset
based on the predictive parameter is added to the resultant signal.
With this operation, a reference picture signal is generated.
Subsequently, the generated reference picture signal is
motion-compensated for by using the motion vector indicated by the
motion vector information 414, thereby generating a prediction
picture signal 412.
(About Frame Memory/Prediction Picture Generator 308)
[0056] FIG. 6 shows the detailed arrangement of the frame
memory/prediction picture generator 308 in FIG. 5. Referring to
FIG. 6, the reproduction video signal 310 output from the adder 306
in FIG. 5 is stored in the frame memory set 402 under the control
of a memory controller 401. The frame memory set 402 has a
plurality of (N) frame memories FM1 to FMN for temporarily holding
the reproduction video signal 310 as a reference frame.
[0057] A predictive parameter controller 403 has in advance
combinations of reference frame numbers and predictive parameters
as a table like the one shown in FIG. 3. The predictive parameter
controller 403 selects a combination of the reference frame number
of a reference frame and a predictive parameter, which are used to
generate the prediction picture signal 412, on the basis of the
index information 415 from the variable-length decoder 303 in FIG.
5. A plurality of multi-frame motion compensators 404 generate a
reference picture signal in accordance with a combination of a
reference frame number and index information, which is selected by
the predictive parameter controller 403, and performs
motion-compensation for each block using this reference picture
signal in accordance with the motion vector indicated by the motion
vector information 414 from the variable-length decoder 303 in FIG.
5, thereby generating the prediction picture signal 412.
Second Embodiment
[0058] The second embodiment of the present invention will be
described next with reference to FIGS. 7 and 8. Since the overall
arrangements of a video encoding apparatus and video decoding
apparatus in this embodiment are almost the same as those in the
first embodiment, only the differences from the first embodiment
will be described.
[0059] In this embodiment, there is described an example of the
manner of expressing predictive parameters based on a scheme of
capable of designating a plurality of reference frame numbers in
accordance with mode information of a macroblock basis. A reference
frame number is discriminated by the mode information for each
macroblock. This embodiment therefore uses a table of predictive
parameters as shown in FIGS. 7 and 8 instead of using a table of
combinations of reference frame numbers and predictive parameters
as in the first embodiment. That is, index information does not
indicate a reference frame number, and only a combination of
predictive parameters is designated.
[0060] The table in FIG. 7 shows an example of a combination of
predictive parameters when the number of reference frames is one.
As predictive parameters, (the number of reference frames+1)
parameters, i.e., two parameters (one weighting factor and one
offset), are designated for each of a luminance signal (Y) and
color difference signals (Cb and Cr).
[0061] The table in FIG. 8 shows an example of a combination of
predictive parameters when the number of reference frames is two.
In this case, as predictive parameters, (the number of reference
frames+1) parameters, i.e., three parameters (two weighting factors
and one offset), are designated from each of a luminance signal (Y)
and color difference signals (Cb and Cr). This table is prepared
for the encoding side and decoding side each as in the first
embodiment.
Third Embodiment
[0062] The third embodiment of the present invention will be
described with reference to FIGS. 9 and 10. Since the overall
arrangements of a video encoding apparatus and video decoding
apparatus in this embodiment are almost the same as those in the
first embodiment, only the differences from the first and second
embodiments will be described below.
[0063] In the first and second embodiments, a video is managed on a
frame basis. In this embodiment, however, a video is managed on a
picture basis. If both a progressive signal and an interlaced
signal exist as input picture signals, pictures are not necessarily
encoded on a frame basis. In consideration of this, a picture
assumes (a) a picture of one frame of a progressive signal, (b) a
picture of one frame generated by merging two fields of an
interlaced signal, or (c) a picture of one field of an interlaced
signal.
[0064] If a picture to be encoded is a picture with a frame
structure like (a) or (b), a reference picture used in motion
compensation prediction is also managed as a frame regardless of
whether the encoded picture, which is the reference picture, has a
frame structure or field structure. A reference picture number is
assigned to this picture. Likewise, if a picture to be encoded is a
picture with a field structure like (c), a reference picture used
in motion compensation prediction is also managed as a field
regardless of whether the encoded picture, which is the reference
picture, has a frame structure or field structure. A reference
picture number is assigned to this picture.
[0065] Equations (4), (5), and (6) are examples of predictive
equations for reference picture numbers and predictive parameters,
which are prepared in the predictive parameter controller 203.
These examples are predictive equations for generating a prediction
picture signal by motion compensation prediction using one
reference picture signal.
Y=clip((D.sub.1(i).times.R.sub.Y(i)+2.sup.L.sup.Y.sup.-1)>>L.sub.Y-
+D.sub.2(i)) (4)
Cb=clip((E.sub.1(i).times.(R.sub.Cb(i)-128)+2.sup.L.sup.C.sup.-1)>>-
;L.sub.C+E.sub.2(i)+128) (5)
Cr=clip((F.sub.1(i).times.(R.sub.Cr(i)-128)+2.sup.L.sup.C.sup.-1)>>-
;L.sub.C+F.sub.2(i)+128) (6)
where Y is a prediction picture signal of a luminance signal, Cb
and Cr are prediction picture signals of two color difference
signals, R.sub.Y(i), R.sub.Cb(i), and R.sub.cr(i) are the pixel
values of the luminance signal and two color difference signals of
a reference picture signal with index i, D.sub.1(i) and D.sub.2(i)
are the predictive coefficient and offset of the luminance signal
with index i, E.sub.1(i) and E.sub.2(i) are the predictive
coefficient and offset of the color difference signal Cb with index
i, and F.sub.1(i) and F.sub.2(i) are the predictive coefficient and
offset of the color difference signal Cr with index i. Index i
indicates a value from 0 (the maximum number of reference
pictures--1), and encoded for each block to be encoded (e.g., for
each macroblock). The resultant data is then transmitted to the
video decoding apparatus.
[0066] The predictive parameters D.sub.1(i), D.sub.2(i),
E.sub.1(i), E.sub.2(i), F.sub.1(i), and F.sub.2(i) are represented
by values determined in advance between the video encoding
apparatus and the video decoding apparatus or a unit of encoding
such as a frame, field, or slice, and are encoded together with
encoded data to be transmitted from the video encoding apparatus to
the video decoding apparatus. With this operation, these parameters
are shared by the two apparatuses.
[0067] The equations (4), (5), and (6) are predictive equations
wherein powers of 2, i.e., 2, 4, 8, 16, . . . are selected as the
denominators of predictive coefficients by which reference picture
signals are multiplied. The predictive equations can eliminate the
necessity of division and be calculated by arithmetic shifts. This
makes it possible to avoid a large increase in calculation cost due
to division.
[0068] In equations (4), (5), and (6), ">>" of a >>b
represents an operator for arithmetically shifting an integer a to
the right by b bits. The function "clip" represents a clipping
function for setting the value in "( )" to 0 when it is smaller
than 0, and setting the value to 255 when it is larger than
255.
[0069] In this case, assuming that L.sub.Y is the shift amount of a
luminance signal, and L.sub.C is the shift amount of a color
difference signal. As these shift amounts L.sub.Y and L.sub.C,
values determined in advance between the video encoding apparatus
and the video decoding apparatus are used. The video encoding
apparatus encodes the shift amounts L.sub.Y and L.sub.C, together
with a table and encoded data, in a predetermined unit of encoding,
e.g., a frame, field, or slice, and transmits the resultant data to
the video decoding apparatus. This allows the two apparatuses to
share the shift amounts L.sub.Y and L.sub.C.
[0070] In this embodiment, tables of combinations of reference
picture numbers and predictive parameters like those shown in FIGS.
9 and 10 are prepared in the predictive parameter controller 203 in
FIG. 2. Referring to FIGS. 9 and 10, index i corresponds to
prediction pictures that can be selected for each block. In this
case, four types of prediction pictures are present in
correspondence with 0 to 3 of index i. "Reference picture number"
is, in other words, the number of a local decoded video signal used
as a reference picture.
[0071] "Flag" is a flag indicating whether or not a predictive
equation using a predictive parameter is applied to a reference
picture number indicated by index i. If Flag is "0", motion
compensation prediction is performed by using the local decoded
video signal corresponding to the reference picture number
indicated by index i without using any predictive parameter. If
Flag is "1", a prediction picture is generated according to
equations (4), (5), and (6) by using a local decoded video and
predictive parameter corresponding to the reference picture number
indicated by index i, thus performing motion compensation
prediction. This information of Flag is also encoded, together with
a table and encoded data, by using a value determined in advance
between the video encoding apparatus and the video decoding
apparatus or in a predetermined unit of encoding, e.g., a frame,
field, or slice, in the video encoding apparatus. The resultant
data is transmitted to the video decoding apparatus. This allows
the two apparatuses to share the information of Flag.
[0072] In these cases, a prediction picture is generated by using a
predictive parameter when index i=0 with respect to a reference
picture number 105, and motion compensation prediction is performed
without using any predictive parameter when i=1. As described
above, a plurality of predictive schemes may exist for the same
reference picture number.
[0073] The table shown in FIG. 9 has predictive parameters
D.sub.1(i), D.sub.2(i), E.sub.1(i), E.sub.2(i), F.sub.1(i), and
F.sub.2(i) assigned to a luminance signal and two color difference
signals in correspondence with equations (4), (5), and (6). FIG. 10
shows an example of a table in which predictive parameters are
assigned to only luminance signals. In general, the number of bits
of a color difference signal is not very large compared with the
number of bits of a luminance signal. For this reason, in order to
reduce the amount of calculation required to generate a prediction
picture and the number of bits transmitted in a table, a table is
prepared, in which predictive parameters for color difference
signals are omitted as shown in FIG. 10 and predictive parameters
are assigned to only luminance signals. In this case, only equation
(4) is used as a predictive equation.
[0074] Equations (7) to (12) are predictive equations in a case
wherein a plurality of (two in this case) reference pictures are
used.
P.sub.Y(i)=(D.sub.1(i).times.R.sub.Y(i)+2.sup.L.sup.Y.sup.-1)>>L.s-
ub.Y+D.sub.2(i) (7)
P.sub.Cb(i)(E.sub.1(i).times.(R.sub.Cb(i)-128)+2.sup.L.sup.C.sup.-1)>-
>L.sub.C+E.sub.2(i)+128 (8)
P.sub.Cr(i)=(F.sub.1(i).times.(R.sub.Cr(i)-128)+2.sup.L.sup.C.sup.-1)>-
;>L.sub.C+F.sub.2(i)+128 (9)
Y=clip((P.sub.Y(i)+P.sub.Y(j)+1)>>1) (10)
Cb=clip((P.sub.Cb(i)+P.sub.Cb(i)+1)>>1) (11)
Cr=clip((P.sub.Cr(i)+P.sub.Cr(j)+1))>>1) (12)
[0075] The pieces of information of the predictive parameters
D.sub.1(i), D.sub.2(i), E.sub.1(i), E.sub.2(i), F.sub.1(i),
F.sub.2(i), L.sub.Y, and L.sub.C and Flag are values determined in
advance between the video encoding apparatus and the video decoding
apparatus or encoded, together with encoded data, in a unit of
encoding such as a frame, field, or slice, and are transmitted from
the video encoding apparatus to the video decoding apparatus. This
allows the two apparatuses to share these pieces of
information.
[0076] If a picture to be decoded is a picture having a frame
structure, a reference picture used for motion compensation
prediction is also managed as a frame regardless of whether a
decoded picture as a reference picture has a frame structure or
field structure. A reference picture number is assigned to this
picture. Likewise, if a picture to be programmed is a picture
having a field structure, a reference picture used for motion
compensation prediction is also managed as a field regardless of
whether a decoded picture as a reference picture has a frame
structure or field structure. A reference picture number is
assigned to this picture.
(About Syntax of Index Information)
[0077] FIG. 11 shows an example of a syntax in a case wherein index
information is encoded in each block. First of all, mode
information MODE is present for each block. It is determined in
accordance with the mode information MODE whether or not index
information IDi indicating the value of index i and index
information IDj indicating the value of index D are encoded.
Encoded information of motion vector information MVi for the motion
compensation prediction of index i and motion vector information
MVj for the motion predictive compensation of index j is added as
motion vector information for each block after encoded index
information.
(About Data Structure of Encoded Bit Stream)
[0078] FIG. 12 shows a specific example of an encoded bit stream
for each block when a prediction picture is generated by using one
reference picture. The index information IDi is set after mode
information MODE, and the motion vector information MVi is set
thereafter. The motion vector information MVi is generally
two-dimensional vector information. Depending on a motion
compensation method in a block which is indicated by mode
information, a plurality of two-dimensional vectors may further be
sent.
[0079] FIG. 13 shows a specific example of an encoded bit stream
for each block when a prediction picture is generated by using two
reference pictures. Index information IDi and index information IDj
are set after mode information MODE, and motion vector information
MVi and motion vector information MVj are set thereafter. The
motion vector information MVi and motion vector information j are
generally two-dimensional vector information. Depending on a motion
compensation method in a block indicated by mode information, a
plurality of two-dimensional vectors may be further sent.
[0080] Note that the above structures of a syntax and bit stream
can be equally applied to all the embodiments.
Fourth Embodiment
[0081] The fourth embodiment of the present invention will be
described next with reference to FIGS. 14 and 15. Since the overall
arrangements of a video encoding apparatus and video decoding
apparatus in this embodiment are almost the same as those in the
first embodiment, only differences from the first, second, and
third embodiments will be described. In the third embodiment,
encoding on a frame basis and encoding on a field basis are
switched for each picture. In the fourth embodiment, encoding on a
frame basis and encoding on a field basis are switched for each
macroblock.
[0082] When encoding on a frame basis and encoding on a field basis
are switched for each macroblock, the same reference picture number
indicates different pictures, even within the same picture,
depending on whether a macroblock is encoded on the frame basis or
on the field basis. For this reason, with the tables shown in FIGS.
9 and 10 used in the third embodiment, a proper prediction picture
signal may not be generated.
[0083] In order to solve this problem, in this embodiment, tables
of combinations of reference picture numbers and predictive
parameters like those shown in FIGS. 14 and 15 are prepared in a
predictive parameter controller 203 in FIG. 2. Assume that when a
macroblock is to be encoded on the field basis, the same predictive
parameter as that corresponding to a reference picture number
(reference frame index number) used when the macroblock is encoded
on the frame basis is used.
[0084] FIG. 14 shows a table used when the macroblock is encoded on
a field basis and a picture to be encoded is a top field. The upper
and lower rows of each field index column correspond to the top
field and bottom field, respectively. As shown in FIG. 14, frame
index j and field index k are related such that when k=2j in the
top field, k=2j+1 in the bottom field. Reference frame number m and
reference field number n are related such that when n=2m in the top
field, n=2m+1 in the bottom field.
[0085] FIG. 15 shows a table used when the macroblock is encoded on
a field basis, and a picture to be encoded is a bottom field. As in
the table shown in FIG. 14, the upper and lower rows of each field
index column correspond to a top field and the bottom field,
respectively. In the table in FIG. 15, frame index j and field
index k are related such that when k=2+1 in the top field, k=2j in
the bottom field. This makes it possible to assign a small value as
field index k to an in-phase bottom field. The relationship between
reference frame number m and reference field number n is the same
as that in the table in FIG. 14.
[0086] When the macroblock is to be encoded on a field basis, a
frame index and field index are encoded as index information by
using the tables shown in FIGS. 14 and 15. When the macroblock is
to be encoded on a frame basis, only the frame index common to the
tables in FIGS. 14 and 15 is index-encoded as index
information.
[0087] In this embodiment, predictive parameters are assigned to a
frame and field by using one table. However, a table for frames and
a table for fields may be separately prepared for one picture or
slice.
[0088] Each embodiment described above has exemplified the video
encoding/decoding scheme using orthogonal transformation on a block
basis. Even if, however, another transformation technique such as
wavelet transformation is used, the technique of the present
invention which has been described in the above embodiments can be
used.
[0089] Video encoding and decoding processing according to the
present invention may be implemented as hardware (apparatus) or
software using a computer. Some processing may be implemented by
hardware, and the other processing may be performed by software.
According to the present invention, there can be provided a program
for causing a computer to execute the above video encoding or video
decoding or a storage medium storing the program.
* * * * *