Note: Descriptions are shown in the official language in which they were submitted.
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A Device and Method for Providing Inter-Field Motion
Compensation for Chrominance Motion Vectors While Decoding
Motion Pictures
This is a divisional application of Canadian
Patent Application No. 2,439,886 filed on September 5, 2003.
Background of the Invention
Field of the Invention
The present invention relates to a motion picture
encoding device and a motion picture decoding device, which
have an inter-field prediction mode.
Description of the Related Art
Generally, motion picture data is large in size.
Therefore, when motion picture data is transmitted from a
transmitting device to a receiving device or when it is
stored in a storage device, highly efficient encoding is
applied to motion picture data. In this case, "highly
efficient encoding" is an encoding process of converting a
specific data string into another data string, and
compressing the amount of data.
There are two types of motion picture data: one
is mainly composed of only frames and the other is composed
of fields. A prior art for compressing a field image is
mainly described below.
As the highly efficient encoding method of motion
picture data, a frame/field prediction encoding is known.
Fig. 1 shows a block diagram of the configuration
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of the frame/field predictive encoding device.
This encoding method utilizes the fact that a
plurality of segments of motion picture data has high
correlation in a time direction with each other. The
operation shown in Fig. 1 is roughly described below.
A subtracter 39 generates a differential image between
an inputted original image and a predicted image, and
an orthogonal transform unit 31, a quantization unit
32 and a coefficient entropy encoding unit 40 encode
the differential image. An inverse quantization unit
33 and an inverse orthogonal transform unit 34 reproduce
the differential image from the output of the quantization
unit 32. Then, a decoded image generation unit 35 decodes
the encoded image using the reproduced differential image
reproduced by the decoded image generation unit 35 and
thepredicted image used at the time of encoding. Adecoded
image storage unit 36 stores the reproduced image. Then,
motion vector calculation unit 37 calculates a motion
vector between the reproduced image and a subsequent
input image, and a predicted image generation unit 38
generates a predicted image using the motion vector.
The generated motion vector is encoded by a vector entropy
encoding unit 41 and is outputted through aMUX 42 together
with the encoded coefficient data encoded by the
coefficient entropy encoding unit 40. In other words,
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since in motion picture data, there is generally high
similarity between frame/field data at a specific time
and frame/field data at a subsequent time, the
inter-frame/field predictive encoding method utilizes
such a property. For example, in a data transmission
system adopting the inter-frame/field predictive
encoding method, a transmitting device generates motion
vector data indicating displacement from previous
frame/field image to a target frame/field image, and
differential data between a predicted image in the target
frame/field which is generated from the previous
frame/field image using its motion vector data and a
real image in the target frame/field, and transmits the
motion vector data and the differential data to a
receiving device. The receiving device reproduces the
image in the target frame/field from the received motion
vector data and differential data.
So far, the summary of the frame/field predictive
encoding has been described with reference to Fig. 1.
Next, frame predictive encoding and field predictive
encoding are described below.
Figs. 2 and 3 show a format used to encode a field
image that is commonly used in ISO/IEC MPEG-2/MPEG-4
(hereinafter called "MPEG-2" and "MPEG-4",
respectively) and the final committee draft of ITU-T
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H.264/ISO/IEC MPEG-4 Part 10 (Advanced video coding
(AVC)) ("Joint Final Committee Draft (JFCD) of Joint Video
Specification (ITU-T REC, H.264 1 ISO/IEC 14496-10 AVC) ",
JVT-D157, or ISO/IEC JTC1/S029/WG11 MPEG02/N492, July
2002, Klagenfurt, AT)(hereinafter called "AVC FCD"),
which ITU-T and ISO/IEC jointly were standardizing as
of August 2002. Specifically, each frame is composed
of two fields: a top field and a bottom field. Fig. 2
shows the respective positions of a luminance pixels
and a chrominance pixels, and a field to which each pixel
belongs. As shown in Fig. 2, odd number-ordered luminance
lines, such as a first luminance line (50a), a third
luminance line (50b), a fifth luminance line (50c), a
seventh luminance line (50d), etc., belong to the top
field, and even number-ordered lines, such as a second
luminance line (51a), a fourth luminance line (51b),
a sixth luminance line (51c), a eighth luminance line
(51d), etc., belong to the bottom field. Similarly, odd
number-ordered chrominance lines, such as a first
chrominance line (52a) , a third chrominance line (52b) ,
etc., belong to the top field, and even number-ordered
chrominance line, such as a second chrominance (53a),
a fourth chrominance line, etc., belong to the bottom
field.
Each of the top and bottom fields indicates an image
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at a different time. Next, the time/spatial disposition
of the top and bottom fields is described with reference
to Fig. 3.
In Figs. 3 and after, the technology of the present
5 invention relates to the vertical component of a motion
vector. Therefore, in this specification, horizontal
pixel components are not shown, and all the horizontal
components of the motion vector are assumed to be 0 for
convenience sake. However, in order to show conventional
problems and the effects of the present invention, the
positional relation between luminance and chrominance
in each field is accurately shown.
In Fig. 3, the vertical and horizontal axes
represent the pixel position of a vertical component
in each field and the elapse of time, respectively. Since
there is no positional change in a field of the horizontal
component of each image, in Fig. 3, its horizontal pixel
component is not shown nor is described.
As shown in Fig. 3, the pixel position of a
chrominance component deviates from the pixel position
in a field of a luminance component by a quarter vertical
pixel. This is because relationship of pixel positions
as shown in Fig. 2 is achieved when a frame is constructed
from both Top and Bottom fields. If it is based on a
NTSC format, each time interval between adjacent top
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and bottom fields (64a: 65a, 65a: 64b, etc.) is
approximately 1/60 seconds. Each time interval between
two consecutive top fields (64a: 64b, etc.) or between
two consecutive bottom field (65a: 65b, etc.) are
approximately 1/30 seconds.
Next, the frame predictive encoding mode of a field
image and its fieldprediction, which is adopted inMPEG-2
and AVC FCD, are described.
Fig. 4 shows a method for constructing a frame using
two consecutive fields (adjacent top and bottom fields)
in a frame predictive mode.
As shown in Fig. 4, a frame is reconstructed by
two time-consecutive fields (top and bottom fields).
Fig. 5 shows a frame predictive mode.
In Fig. 5 it is assumed that each frame, such as
84a, 84b, 84c, etc., is already reconstructed by two
consecutive fields (top and bottom fields), as shown
in Fig. 4. In this frame predictive mode, a frame to
be encoded which is composed of top and bottom fields
is encoded. As a reference image, one reference frame
is constructed by two consecutive fields (top and bottom
fields) stored for reference use, and is used to predict
the target frame to be encoded. Then, these two frame
images are encoded according to the process flow shown
in Fig. 1. In the expression method of a motion vector
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of this frame predictive encoding mode, a zero vector,
that is, (0,0) indicates a pixel located in the same
spatial position. Specifically, the motion vector (0, 0)
of a luminance pixel 82 that belongs to frame#2(84b)
indicates the pixel position 81 of frame#1(84a).
Next, a field predictive encoding mode is
described.
Fig. 6 shows a predictive method in an inter-field
predictive mode.
In a field predictive mode, an encoding target is
one top field (94a, 94b, etc.) or bottom field (95a,
95b, etc.) that is inputted as an original image. As
a reference image, a top field or bottom field that is
stored before can be used. In this case, it is generally
defined that the fact that an original image field parity
and a reference field parity are the same means that
the original image field and the reference field both
are top fields or bottom fields. For example, in a
prediction 90 between fields with the same parity shown
in Fig. 6, an original image field (94b) and a reference
field (94a) both are top fields. Similarly, it is
generally defined that the fact that an original image
field parity and a reference field parity are different
means that one of original image and reference fields
is a top field and the other is a bottom field. For example,
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in a prediction 91 between different parity fields shown
in Fig. 6, the original image field is a bottom field
(95a) and the reference field is a top field (94a) . Then,
these original image and reference fields are encoded
according to the process flow shown in Fig. 1.
In the prior art, in both frame and field modes,
a motion vector is calculated based on a pixel position
in each frame/field. Here, a conventional motion vector
calculation method and a conventional pixel
corresponding method used when a motion vector is given
are described.
Fig. 7 defines the coordinates of a frame/field
image widely used in MPEG-2 coding, MPEG-1 coding, AVC
FCD coding, etc. White circles in Fig. 7 are pixel
definition positions in target frames/fields. In the
coordinates of this frame/field image, the upper left
corner is designated as the origin (0,0), and values
1, 2, 3, etc., are sequentially assigned to both
horizontal and vertical pixel definition positions.
Specifically, the coordinates of a pixel that are located
at the n-th horizontal position and the m-th vertical
position are (n,m). Similarly, the coordinates of a
position interpolated among the pixels are also defined.
Specifically, since a position 180 marked with a black
circle in Fig. 7 is located at 1.5 pixels in the horizontal
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direction from the pixel located in the upper left corner
and at 2 pixels in the vertical direction, the coordinates
of the position 180 is expressed as (1 .5, 2) . In a field
image, there are only a half of the pixels of a frame
image in the vertical direction. However, even in this
case, the coordinates of a pixel are defined in the same
way as in Fig. 7, based on pixel positions located in
each field.
Next, the definition of a motion vector between
fields is described using the coordinate system shown
in Fig. 7.
Fig. 8 shows a conventional calculation method of
a motion vector between corresponding pixels between
fields. The definition of a motion vector requires the
position of a coding field and the position of a reference
field. Amotion vector is defined between these two points.
Thus, a motion vector between a coding field coordinates
201 (X5, Y5) and a reference field coordinates 202 (Xd, Yd)
is calculated. In the conventional calculation method
of a motion vector between pixels corresponding to
between-fields, a motion vector is calculated by the
same method described below, regardless of whether the
coding field or reference field is atop field or a bottom
field. Specifically, coding field coordinates 201 (X5, YS)
and reference field coordinates 202 (Xd, Yd) are inputted
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to a motion vector calculation unit 200, and as a motion
vector 203 between these two points, (Xd-Xs, Yd-Ys) is
given.
Fig. 9 shows a conventional method for calculating
5 a pixel that is pointed by a motion vector defined between
fields. In this case, it is assumed that a motion vector
is calculated by the method shown in Fig. 8. The
calculation of reference frame/field coordinates
requires a coding frame/ fieldposition and a motion vector.
10 In the case shown in Fig. 9, it is assumed that a motion
vector 211(X,Y) is given for coding field coordinates
212 (X5, Y5) , and reference field coordinates can be
calculated using both the motion vector 212(X,Y) and
the coding field coordinates 212 (XS, YS) . In the
conventional calculation method of a motion vector
between corresponding pixels between fields, a reference
field position is calculated by the same method described
below, regardless of whether the coding field or
reference field is a top field or a bottom field.
Specifically, a motion vector 211 (X, Y) and coding field
coordinates 212 (X5, Y5) are inputted to a pixel
corresponding unit 210, and as reference field
coordinates 213, coordinates (XS+X,YS+Y) is given.
The definition of the relation between a vector
and a pixel position applies to both a luminance component
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and chrominance component. In MPEG-1/MPEG-2/AVC FCD,
which all are general motion picture encoding methods,
only the vector of a luminance component is encoded,
and the vector of a chrominance component is calculated
by scaling down the luminance component. Particularly,
in AVC FCD, since the number of vertical pixels and that
of horizontal pixels of a chrominance component are a
half of those of a luminance component, respectively,
it is specified that a motion vector used to calculate
the predictive pixel of a chrominance component should
be obtained by accurately scaling down the motion vector
of the luminance component to a half.
Fig. 10 shows a conventional method for calculating
a chrominance motion vector using a luminance motion
vector.
Specifically, if a luminance motion vector 221 and
a chrominance motion vector 222 are (MV x,MV y) and (MVC x,
MVC_y), respectively, a chrominance motion vector
generation unit 220 can calculate a chrominance motion
vector 222 according to the following equation.
(MVC x, MVC y) = (MV x/2,MV y/2) (1)
This conventional calculation method can be used
regardless of whether a motion vector is used for
predicttionbetween fields with the same parity or between
fields with different parity.
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In AVC FCD, as the accuracy of the motion vector
of a luminance component, 1/4 pixel accuracy can be
applied. Therefore, as a result of equation (1) , as the
accuracy of the motion vector of a chrominance component,
a vector having 1/8 pixel accuracy, that is, accuracy
at the decimal fraction, can be used.
Fig. 11 shows the calculation method of the
interpolated pixel of a chrominance component that is
defined in AVC FCD.
In Fig. 11, a black circle and a white circle
represent an integer pixel and an interpolated pixel,
respectively. In this case, the horizontal coordinate
of an interpolated pixel G (256) is obtained by internally
dividing each horizontal coordinate between points
A(250) and C(252) at a ratio a:l-a, and the vertical
coordinate can be obtained by internally dividing each
vertical coordinate between points A(250) and B(251)
at (3:1-(3. In this case, a and 0 are a value between 0
and 1. An interpolated pixel G(256) defined by such
positions can be roughly calculated as follows using
integer pixels A (250) , B (251) , C (252) and D (253) , which
are located around the interpolated pixel G(256), and
using a and j3.
G = (1-(x) = (1-0) =A + (1-(X) =a=B + a= (1-(3) =C + a=0=D
(2)
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The interpolated pixel calculation method of a
chrominance component, using the method shown in Fig.
11 is just one example, and there is no problem in using
another calculation method.
In the case of this field encoding mode, in a
prediction in which an original image field and a
reference field are different, that is, between fields
with different parity, the respective zero vectors of
the motion vector of a luminance component and that of
a chrominance component are not parallel inthe definition
of AVC FCD. Specifically, if a prediction is made using
the motion vector of a chrominance component calculated
using themotion vector of a luminance component according
to the conventional definition, a pixel located in a
position spatially deviated from that of the luminance
component is to be referenced. This fact is described
below with reference to Fig. 12. In Fig. 12, it is assumed
that a top field 130, a bottom field 131 and a top field
132 continue timewise. In this case, bottom field 131
is to be encoded using top field 130. In this inter-field
encoding, the vertical motion vector in the same line
of each field is defined to be zero. Therefore, if a
zero vector (0, 0) is assigned to a luminance pixel 133a
that belongs to the second line of bottom field 131,
this pixel can be predicted from a pixel 135a in top
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field 130. Similarly, when a zero vector (0, 0) is assigned
to a chrominance pixel 133a which belongs to the first
line of the bottom field 131, this pixel is predicted
from the pixel 137a which is in the first line of
chrominance of the top field 130.Similarly, a luminance
pixel 133b in the third line and a chrominance pixel
134b, which belong to top field 132 are predicted from
pixels 135b in the third line of luminance and 137b in
the second line of chrominance in bottom field 131,
respectively. Since essentially it is preferable that
a chrominance motion vector and a luminance motion vector
are parallel, chrominance pixels 134a and 134b should
be predicted from the positions 136a and 136b,
respectively, if a luminance motion vector is as it is.
As described earlier, in a prediction between
fields with dif ferent parity, the fact that the respective
zero vectorsofluminance and chrominance are not parallel
is explained. In the case of AVC FCD, this fact causes
the following problems for all vectors in a prediction
between fields with different parity. Figs. 13 and 14
show such problems. Problems in the case of AVC FCD are
described below. In the explanation below, a horizontal
component of a motion vector is set to zero in all cases
for brevity.
Fig. 13 shows a conventional problem caused if a
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chrominance motion vector is conventionally calculated
using a luminance motion vector when a reference field
and a coding field are a bottom field and a top field,
respectively. InAVC FCD, since, as is clear from equation
5 (1), it is specified that the number of vertical and
horizontal pixels of a chrominance component are a half
of those of a luminance component, a motion vector used
to calculate the predictive pixel of a chrominance should
be scaled down to a half of the motion vector of a luminance
10 component. This is regardless of whether a motion vector
is used for prediction between frames, between fields
with the same parity or between fields with different
parity.
It is shown below that this definition causes a
15 problem when a chrominance motion vector is calculated
using a luminance motion vector defined between fields
with different parity. In Fig. 13, a coding field top
field luminance pixel 140 in the first line has (0,1)
as a predictive vector, and as a result, it points to a
bottom reference field luminance pixel position 141 in
the second line as a predictive value.
In this case, a chrominance motion vector that
belongs to the same block is calculated to be (0, 1/2),
according to equation (1) . If a prediction is made using
motion vector (0, 1/2) as a predictive value of a coding
1
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field top field chrominance pixel 142 in the first line,
a pixel position 143 is used as predicted value, which
shifts downward by half a pixel from a. pixel in the first
line of a bottom reference field chrominance component.
In this case, a luminance motion vector (0, 1) and
a chrominance vector (0,1/2) are not parallel. It is
preferable to use a bottom reference field chrominance
predictive pixel position 145 to which a chrominance
motion vector parallel to a luminance motion vector is
applied.
Fig. 14 shows a conventional problem caused if a
chrominance motion vector is calculated using a luminance
motion vector when a reference field and a coding field
are a top field and a bottom field, respectively. As
described in Fig. 13, in Fig. 14, a bottom coding field
luminance pixel 150 in the first line has (0,1) as a
predictive vector, and as a result, it points a reference
top field luminance pixel position 151 in the second
line as a predictive value.
In this case, a chrominance motion vector that
belongs to the same block is calculated to be (0, 1/2) ,
according to equation (1) . If a prediction is made using
motion vector (0, 1/2) as a predictive value of a bottom
coding field chrominance pixel 152, a pixel position
153 is used as predicted value which is shifted by half
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a pixel from a top reference field chrominance pixel
position 153 in the first line.
In this case, a luminance motion vector (0, 1) and
a chrominance vector (0,1/2) are not parallel. It is
preferable to use a top reference field chrominance
predictive pixel position 155 to which a chrominance
motion vector parallel to a luminance motion vector is
applied.
As described above, if a reference field parity
and a coding field parity are different, according to
the conventional predictive method, a pixel located in
the position of a luminance component spatially deviated
from that of the chrominance component is to be referenced,
and a predictive image, in which a pixel located in the
position of a luminance component is spatially deviated
from that of the chrominance component, is generated
not only for a zero vector but for all the vectors. Note
that, in the above explanation, vectors are said to be
parallel or not parallel by considering the case where
the direction in time of a luminance motion vector and
a chrominance motion vector, that is, time direction
from coding field to reference field in included in a
motion vector. The same is true below.
1
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Summary of the Invention
It is an object of some embodiments of the present
invention to provide a motion picture encoding device and a
motion picture decoding device capable of particularly
improving predictive efficiency of a chrominance component
and improving encoding efficiency accordingly, in encoding
between different field images.
According to the present invention, there is
provided a motion picture decoding method for performing a
decoding process on a motion picture signal by making an
inter-field motion compensation with a motion vector of which
a reference field is Top and of which a decoding field is
Bottom, each frame of the motion picture signal being composed
of two fields, the number of pixels in a chrominance vertical
component of the motion picture signal being different from
the number of pixels in a luminance vertical component of the
motion picture signal, wherein an inter-field motion
compensation is made using a motion vector of luminance
component and a motion vector of chrominance component, the
motion vector of luminance component and the motion vector of
chrominance component satisfying (MVCx, MVCy) = (MVx, MVy+2)
when a horizontal component and vertical component of
luminance component motion vector, indicating a displacement
of one luminance pixel of a field image by a value of "4" of a
vector component as units, are respectively MVx and MVy and
when a horizontal component and vertical component of
chrominance component motion vector indicating a displacement
of one chrominance pixel of a field image by a value of "8" of
a vector component as units, are respectively MVCx and MVCy.
i
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According to the present invention, there is also
provided a motion picture decoding device for performing a
decoding process on a motion picture signal by making an
inter-field motion compensation with a motion vector of which
a reference field is Top and of which a decoding field is
Bottom, each frame of the motion picture signal being composed
of two fields, the number of pixels in a chrominance vertical
component of the motion picture signal being different from
the number of pixels in a luminance vertical component of the
motion picture signal, wherein an inter-field motion
compensation is made using a motion vector of luminance
component and a motion vector of chrominance component, the
motion vector of luminance component and the motion vector of
chrominance component satisfying (MVCx, MVCy) = (MVx, MVy+2)
when a horizontal component and vertical component of
luminance component motion vector, indicating a displacement
of one luminance pixel of a field image by a value of "4" of a
vector component as units, are respectively MVx and MVy and
when a horizontal component and vertical component of
chrominance component motion vector, indicating a displacement
of one chrominance pixel of a field image by a value of "8" of
a vector component as units, are respectively MVCx and MVCy.
A motion picture encoding device for making inter-
field motion compensation of a motion picture signal
composed of a plurality of fields comprises a plurality of
chrominance motion vector generation units generating a
chrominance motion vector using a luminance motion vector in
a motion picture encoding device; and a selection unit
selecting one of the chrominance motion vector generation
units used to generate a chrominance vector, using the
i
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reference field parity and coding field parity of a motion
vector. The chrominance motion vector generation unit
selected by the selection unit generates the chrominance
predictive vector, based on the motion vector information of
luminance information.
The motion picture decoding device of some
embodiments of the present invention for making the inter-field
motion compensation of a motion picture signal composed of a
plurality of fields comprises a plurality of chrominance motion
vector generation units generating a chrominance motion vector
from a luminance motion vector; and a selection unit selecting
one of the chrominance motion vector generation units used to
generate a chrominance vector, using the reference field parity
and coding field parity of a motion vector. The chrominance
motion vector generation unit selected by the selection unit
generates the chrominance predictive vector, based on the
motion vector information of luminance information.
According to some embodiments of the present
invention, since a chrominance motion vector which is generated
by a suitable method based on parities of an encoding/decoding
field and a reference field, is used, the discrepancy of the
chrominance motion vector caused by the difference of
arrangement, or the way of assignment to a top and a bottom
field of luminance pixels and chrominance pixels, is resolved.
Additionally, by some embodiments of the present
invention, a chrominance motion vector which is parallel to a
luminance motion vector is obtained even in the case of fields
with different parity, and the problem of a shift of reference
pixel position between luminance components and chrominance
components in the conventional method, is resolved.
1
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Brief Description of the Drawings
Fig. 1 shows the configuration of an inter-frame
predictive encoding device;
Fig. 2 shows the respective positions of luminance
5 and chrominance pixels and a field to which each of them
belongs;
Fig. 3 shows the respective vertical time and
spatial positions of luminance and chrominance pixels
in a field image;
10 Fig. 4 shows the relation between a field and a
frame in a frame encoding mode;
Fig. 5 shows a predictive method in an inter-frame
predictive encoding mode;
Fig. 6 shows a predictive method in an inter-field
15 predictive mode;
Fig. 7 shows the coordinates of a field image;
Fig. 8 shows the conventional calculation method
of a motion vector between corresponding pixels between
fields;
20 Fig. 9 shows the conventional calculation method
of a pixel pointed by a motion vector;
Fig. 10shows a conventional method for calculating
a chrominance motion vector, using a luminance motion
vector;
Fig. 11 shows the calculation method of an
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interpolated pixel of a chrominance component;
Fig. 12 shows the principle of conventional direct
mode for explaining a zero vector between fields with
different parity;
Fig. 13 shows a conventional problem caused if a
chrominance motion vector is calculated using a luminance
motion vector when a reference field and a coding field
are a bottom field and a top field, respectively;
Fig. 14 shows a conventional problem caused if a
chrominance motion vector is calculated using a luminance
motion vector when a reference field and a coding field
are a top field and a bottom field, respectively;
Fig. 15 shows the method for generating a
chrominance motion vector, using a luminance motion
vector in an embodiment of the present invention;
Fig. 16 shows the operation of one preferred
embodiment of the first chrominance motion vector
generation unit of the present invention;
Fig. 17 shows the operation of one preferred
embodiment of the second chrominance motion vector
generation unit of the present invention;
Fig. 18 is the operation of one preferred embodiment
of the third chrominance motion vector generation unit
of the present invention;
1
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22
Fig. 19 is the operation of one preferred embodiment
of the selection unit of the present invention;
Fig. 20 is one example of the present invention
which calculates a chrominance motion vector using a
luminance motion vector when a reference field and a
coding field are bottom and top fields, respectively;
and
Fig. 21 is one example of the present invention
which calculates a chrominance motion vector using a
luminance motion vector when a reference field and a
coding field are top and bottom fields, respectively.
Fig. 22 shows the operation of another preferred
embodiment of the first chrominance motion vector
generation unit of the present invention;
Fig. 23 shows the operation of another preferred
embodiment of the second chrominance motion vector
generation unit of the present invention;
Fig. 24 is the operation of another preferred
embodiment of the third chrominance motion vector
generation unit of the present invention;
Description of the Preferred Embodiments
Firstly, the principle of coding in the present
invention is described.
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The motion picture encoding device of the present
invention for making the inter-field motion compensation
of a motion picture signal composed of a plurality of
fields comprises a plurality of chrominance motion vector
generation units generating a chrominance motion vector
using a luminance motion vector; and a selection unit
selecting one of the chrominance motion vector generation
units used to generate a chrominance vector, using the
respective parity of the reference field and a coding
field of a motion vector. The chrominance motion vector
generation unit selected by the selection unit generates
the chrominance predictive vector, based on the motion
vector information of luminance information.
If a chrominance motion vector from a coding field
to a reference field is parallel to a luminance motion
vector from the coding field to the reference field,
the spatial shift of the luminance motion vector and
that of the chrominance motion vector become the same,
that is, the relation of the spatial positions of the
luminance motion vector and the chrominance motion vector
is preserved, then the color displacement between fields
disappears.
Here, the important thing is that, in conventional
method, even if the luminance motion vector is parallel
to the chrominance motion vector based on a mathematical
CA 02591682 2007-06-29
24
expression, each does not become parallel when those
vectors are mapped on relations between luminance pixels
and between chrominance pixels which compose each field.
The plurality of chrominance motion vector
generation units include the three following types.
Afirst chrominance motion vector generation unit
is selected by the selection unit when a reference field
and a coding field have the same parity. A second
chrominance motion vector generation unit is selected
by the selection unit when a reference field and a coding
field are a top field and a bottom field, respectively.
A third chrominance motion vector generation unit is
selected by the selection unit when a reference field
and a coding field are a bottom field and a top field,
respectively.
A method for calculating a chrominance motion
vector parallel to a luminance motion vector depends
on the coding field parity and reference field parity
of a luminance motion vector. The calculation method
differs in the following three case: a case where the
coding field parity and reference field parity are the
same, a case where the coding field and reference field
are top and bottom fields, respectively, and a case where
the coding field and reference field are bottom and top
fields, respectively. Therefore, in the present
CA 02591682 2007-06-29
invention, an optimal one is selected from the three
types of chrominance motion vector generation units
calculating a chrominance motion vector parallel to a
luminance motion vector, depending on the coding field
5 and the reference field, and a chrominance motion vector
is generated.
Specifically, if the reference field parity and
coding field parity are the same, the first chrominance
motion vector generation unit calculates a chrominance
10 motion vector asfollows,assumingthat a luminance motion
vector indicating the vertical displacement of one
luminance pixel of a field image by the value "1" of
the vector component as units and a chrominance motion
vector indicating the vertical displacement of one
15 chrominance pixel of a field image by the value "1" of
the vector component as units are MVy and MVCy,
respectively.
MVCy = Mvy/2 (3)
If the reference field parity and coding field
20 parity are topandbottomfields, respectively, the second
chrominance motion vector generation unit calculates
a chrominance motion vector as follows, assuming that
a luminance motion vector indicating the vertical
displacement of one luminance pixel of a field image
25 by the value "1" of the vector component as units and
CA 02591682 2007-06-29
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a chrominance motion vector indicating the vertical
displacement of one chrominance pixel of a field image
by the value "1" of the vector component as units are
MVy and MVCy, respectively.
MVCy = Mvy/2 + 0.25 (4)
If the reference field parity and coding field
parity are bottom and top fields, respectively, the third
chrominance motion vector generation unit calculates
a chrominance motion vector as follows, assuming that
a luminance motion vector indicating the vertical
displacement of one luminance pixel of a field image
by the value "1" of the vector component as units and
a chrominance motion vector indicating the vertical
displacement of one chrominance pixel of a field image
by the value "1" of the vector component as units are
MVy and MVCy, respectively.
MVCy = Mvy/2 - 0.25 (5)
Sometimes, the respective units of luminance and
chrominance vectors vary, depending on its definition.
In the case that it is defined that a luminance motion
vector indicates the displacement of one luminance moving
pixel when the component of the luminance motion vector
changes by value 4 and that a chrominance motion vector
indicates the displacement of one chrominance moving
pixel when the component of the chrominance motion vector
CA 02591682 2007-06-29
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changes by value 8, if the reference field parity and
coding field parity are the same, the first chrominance
motion vector generation unit calculates a chrominance
motion vector as follows, assuming that a luminance motion
vector and a chrominance motion vector are MVy and MVCy,
respectively.
MVCy = Mvy (6)
In the same definition, if the parity of reference
field and coding field are top and bottom fields,
respectively, the second chrominance motion vector
generation unit calculates a chrominance motion vector
as follows, assuming that a luminance motion vector and
a chrominance motion vector are MVy and MVCy,
respectively.
MVCy = Mvy + 2 (7)
In the same definition, if the reference field
parity and coding field parity are bottom and top fields,
respectively, the third chrominance motion vector
generation unit calculates a chrominance motion vector
as follows, assuming that a luminance motion vector and
a chrominance motion vector are MVy and MVCy,
respectively.
MVCy = Mvy - 2 (8)
The motion picture decoding device of the present
invention basically has the same functions as the motion
CA 02591682 2007-06-29
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picture encoding device, and operates in the same way.
The preferred embodiments of the encoding device
are mainly described below. The encoding device has the
configuration described above. Since the present
invention relates to the vertical component of a motion
vector, it is assumed for convenience sake that the
horizontal components of all the motion vectors are 0.
In this case, the decoding device has the same
configuration as the encoding device.
Preferred embodiments are described below
assuming that AVC FCD is adopted.
Fig. 15 shows amethod for calculating a chrominance
motion vector using a luminance motion vector. The
preferred embodiment of a device generating a chrominance
motion vector using a luminance motion vector in a field
prediction comprises three types of chrominance motion
vector generation units and one selection unit.
The operation of the present invention shown in
Fig. 15 is described below. Firstly it is assumed that
a given luminance motion vector 231 is (MV_x,MV_y) . This
luminance vector is inputted to all of a first chrominance
motion vector generation unit 233, a second chrominance
motion vector generation unit 234 and a third chrominance
motion vector generation unit 235. Then, their respective
outputs are inputted to a selection unit 230. The
CA 02591682 2007-06-29
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selection unit 230 selects one of the respective outputs
of the first, second and third chrominance motion vector
generation units, based on information about the coding
field parity 237 of the inputted motion vector and its
reference field parity 238, and outputs it as a color
motion vector 232 (MVC x,MVC y).
Fig. 16 shows the operation of the first chrominance
motion vector generation unit. In this preferred
embodiment, a luminance motion vector 261 (MV x,MV y)
is inputted to a first chrominance motion vector
generation unit 260, anda first chrominance motion vector
candidate 262 (MVC1 x, MVC1 y) is outputted. The
chrominance motion vector generation unit 260 calculates
the first chrominance motion vector candidate 262 as
follows using the luminance motion vector 261.
(MVC1 x, MVC1 y) = (MV x/2, MV y/2) (9)
Then, the calculated first chrominance motion vector
candidate 262 is outputted to the selection unit.
Fig. 17 shows the operation of the second
chrominance motion vector generation unit. In this
preferred embodiment, a luminance motion vector 271
(MV_x, MV_y) is inputted to a second chrominance motion
vector generation unit 270, and a second chrominance
motion vector candidate 272(MVC2_x,MVC2_y)isoutputted.
The chrominance motion vector generation unit 270
CA 02591682 2007-06-29
calculates the second chrominance motion vector candidate
272 as follows using the luminance motion vector 271.
(MVC2_x, MVC2_y) _ (MV-x/2, MV_y/2+1/4) (10)
Then, the calculated second chrominance motion vector
5 candidate 272 is outputted to the selection unit.
Fig. 18 shows the operation of the third
chrominance motion vector generation unit. In this preferred
embodiment, a luminance motion vector 281 (MV`x,MV_y) is
inputted to a third chrominance motion vector generation
10 unit 280, and a third chrominance motion vector candidate
282 (MVC3_x, MVC3_y) is outputted. The chrominance motion
vector generation unit 280 calculates the third chrominance
motion vector candidate 282 as follows using the luminance
motion vector 281.
15 (MVC3_x,MVC3_y) = (MV x/2,MV y/2-1/4) (11)
Then, the calculated third chrominance motion vector
candidate 282 is outputted to the selection unit.
Fig. 19 shows the operation of one preferred
embodiment of the selection unit 240 of the present
20 invention. Firstly, in this preferred embodiment, a
condition judgment table 241 is used for judgment of the
coding field parity 247 of a motion vector and its reference
field parity 248, and the selection information 249 of a
chrominance motion vector generation unit to
CA 02591682 2007-06-29
31
be selected is outputted. In this preferred embodiment,
if the reference field and coding field are the same,
this condition judgment table 241 is used for outputting
selection information indicating the selection of a first
chrominance motion vector candidate 244. If reference
field and coding field are top and bottom fields,
respectively, the condition judgment table 241 is used
.for outputting selection information indicating the
selection of a second chrominance motion vector candidate
245. If reference field and coding field are bottom and
top fields, respectively, the condition judgment table
241 is used for outputting selection information
indicating the selection of a third chrominance motion
vector 246 candidate.
In this case, the first, second or third
chrominance motion vector candidates 244, 245 and 246
are connected to 262 shown in Fig. 16, 272 shown in Fig.
17 and 282 shown in Fig. 18, respectively. Then, a selector
243 selects one of the first, second and third chrominance
motion vector candidates 244, 245 and 246, based on the
selection information 249, and outputs (MVC x,MVC y)
as its chrominance motion vector 242.
Fig. 20 shows the operation of the present invention
to calculate a chrominance vector using a luminance vector
in the case where reference field and coding field are
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32
bottom and top fields, respectively. In the example shown
in Fig. 20, a luminance motion vector (MV x,MV y) used
to predict a top coding field pixel 160 is assumed to
be (0, 1) . In this case, a reference field bottom field
luminance pixel position 161 is selected for the
prediction of a luminance pixel 160. The calculation
process of a chrominance motion vector to be used to
predict a top coding field chrominance pixel 162 is
described below with reference to Fig. 15.
Firstly, in Fig. 20, reference field and coding
field are bottom and top fields, respectively. In this
case, the condition judgment table 241 shown in Fig.
19 is used for selecting selection information 249 about
the third chrominance motion vector candidate. According
to equation (11), the third chrominance motion vector
candidate is calculated as follows.
(MVC3 x,MVC3 y) = (MV x/2,MV y/2-1/4)
= (0/2,1/2-1/4)
= (0,1/4) (12)
Then, this value is outputted as the chrominance motion
vector 242 shown in Fig. 19. If this vector (0,1/4) is
applied to the top coding field chrominance pixel 162,
a bottom reference field chrominance pixel position 163
is used as a predicted value. In Fig. 20, the vertical
positional relation between pixels corresponds to a real
CA 02591682 2007-06-29
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pixel. As is clear from Fig. 20, a luminance motion vector
(0, 1) and a chrominance motion vector (0, 1/4) are paral lel .
Thus, the color deviation between luminance and
chrominance components, which is a conventional problem,
can be solved by the present invention.
Similarly, Fig. 21 shows the operation of the
present invention to calculate a chrominance vector using
a luminance vector in the case where reference field
and coding field are top and bottom fields, respectively.
In the example shown in Fig. 21, a luminance motion
vector (MV_x,MV_y) used to predict a bottom coding field
pixel 170 is assumed to be (0, 1) . In this case, a top
reference field luminance pixel position 171 is selected
for the prediction of a luminance pixel 170. The
calculation process of a chrominance motion vector to
be used to predict a bottom coding field chrominance
pixel 172 is described below with reference to Fig. 15.
Firstly, in Fig. 21, reference field and coding
field are top and bottom fields, respectively. In this
case, the condition judgment table 241 shown in Fig.
19 is used for selecting selection information 249 about
the second chrominance motion vector candidate.
According to equation (10), the candidate second
chrominance motion vector is calculated as follows.
(MVC2_x,MVC2_y) _ (MV_x/2,MV_y/2+1/4)
CA 02591682 2007-06-29
34
= (0/2,1/2+1/4)
(0,3/4) (13)
Then, this value is outputted as the chrominance motion
vector 242 shown in Fig. 19. If this vector (0,3/4) is
applied to the bottom coding field chrominance pixel
172, a top reference field chrominance pixel position
173 is used as a predictive position. In Fig. 21, the
vertical positional relation between pixels corresponds
to a real one. As is clear from Fig. 21, a luminance
motion vector (0,1) and a chrominance motion vector
(0,3/4) are parallel. Thus, the color deviation between
luminance and chrominance components, which is a
conventional problem, can be solved by the present
invention.
Although in the examples shown in Figs. 20 and 21,
the prediction of a specific vector is described, in
a prediction between other parity fields, a prediction
in which there is no deviation between luminance and
chrominance can also realized by applying this preferred
embodiment.
When the reference field parity and coding field
parity are the same, such color deviation does not occur.
Therefore, the result of the first chrominance motion
vector generation unit 233 of the present invention which
has the same configuration as a chrominance motion vector
CA 02591682 2007-06-29
generation unit 220 is selected from the conventional
luminance motion vector shown in Fig. 10, and is used
as a color motion vector 232. Since in this case, a
chrominance motion vector calculated by the present
5 invention is the same as conventional one, the description
of this preferred embodiment is omitted here.
In another aspect of the present invention,
equations (9), (10) and (11) vary depending on the units
of luminance and chrominance motion vectors.
10 Figs. 22 through 24 show another embodiment of the
first chrominance motion vector generation unit, the
second chrominance motion vector generation unit and
the third chrominance motion vector generation unit of
the present invention.
15 In the case that it is defined that a luminance
motion vector indicates the displacement of one luminance
moving pixel when the value of the luminance motion vector
changes by four and that a chrominance motion vector
indicates the displacement of one chrominance moving
20 pixel when the value of the chrominance motion vector
changes by eight, a chrominance motion vector generation
unit 260a calculates a candidate first chrominance motion
vector 262a using a luminance motion vector 261a as
follows.
25 (MVC1`x,MVC1_y) = (MV_x,MV y) (14)
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Then, the calculated first chrominance motion vector
candidate 262a is outputted to a selection unit.
The chrominance motion vector generation unit 270a
calculates a second chrominance motion vector candidate
272a using a luminance motion vector 271a as follows.
(MVC2 x,MVC2 y) = (MV x,MV y + 2) (15)
Then, the calculated second chrominance motion vector
candidate 272a is outputted to a selection unit.
The chrominance motion vector generation unit 280a
calculates a third chrominance motion vector candidate
282a using a luminance motion vector 281a as follows.
(MVC3 x,MVC3 y) = (MV x,MV y - 2) (16)
Then, the calculated third chrominance motion vector
candidate 282a is outputted to a selection unit.
Although this preferred embodiment is described
assuming that it adopts AVC FCD, this is just one preferred
embodiment, and the format for encoding a field image
is not limited to this.
According to the present invention, a chrominance
motion vector parallel to a luminance motion vector can
also be calculated in fields with different parity, and
the deviation in a reference pixel position between
luminance and chrominance components, which are the
conventional problem, can be solved accordingly.
