Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-09-15
2001-11-27
Britton, Howard (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240130, C375S240140
Reexamination Certificate
active
06324215
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a motion picture coding and decoding apparatus for coding and decoding motion picture or image data represented in digital manner. More specifically, the present invention relates to a motion picture coding and decoding apparatus free of image degradation.
BACKGROUND ART
In image coding, a method of superimposing different motion picture sequences has been studied. In an article entitled “An Image Coding Scheme Using Layered Representation and Multiple Templates” (Technical Report of IEICE, IE94-159, pp. 99-106 (1995)) discloses a method of forming a new sequence by superimposing a motion picture sequence as a background and a motion picture sequence of a component motion picture or image as a foreground (for example, video image of a character or fish cut out by chromakey technique).
An article “Temporal Scalability Based on Image Content”, ISO/IEC/JTC 1/SC29/WG11 MPEG95/211(1995) discloses a method of forming a new sequence by superimposing a motion picture sequence of component motion images having high frame rate on a motion picture sequence having a low frame rate.
According to this method, referring to
FIG. 27
, prediction coding is performed at a low frame rate at a lower layer, and prediction coding is performed at a high frame rate only at a selected area (hatched portion) of an upper layer. However, a frame coded in the lower layer is not coded in the upper layer, but decoded image of the lower layer is copied and used as it is. It is assumed that a portion to which a viewer pays attention, such as a figure or a character is selected as the selected area.
FIG. 26
is a block diagram showing a main portion of a conventional motion picture coding and decoding apparatus. Referring to the left side of
FIG. 26
, in a coding apparatus of the conventional motion picture and encoding apparatus, first and second skipping units
801
and
802
thin out frames of input motion picture data. The input image data thus comes to have lower frame rate and input to upper layer coding unit
803
and lower layer coding unit
804
, respectively. It is assumed that the frame rate for the upper layer is not lower than the frame rate of the lower layer.
Input motion picture as a whole is coded in lower layer coding unit
804
. Internationally standardized method of motion picture coding such as MPEG or H.261 is used as the coding method. A decoded image of the lower layer is formed in lower layer coding unit
804
, which image is utilized for prediction coding and at the same time, input to a superimposing unit
805
.
Only the selected area of the input motion picture is coded in upper layer coding unit
803
of FIG.
26
. The internationally standardized method of motion picture coding such as MPEG or H.261 is also used here. Only the selected area is coded, however, based on area shape information. A frame which has already been coded in the lower layer is not coded in the upper layer. The area shape information represents shape of the selected area such as a figure portion, and is a binary image assuming the value 1 at the position of the selected area and the value 0 at other positions. Only the selected area of the motion picture is coded in upper layer coding unit
803
, and input to superimposing unit
805
.
The area shape is coded utilizing 8 directional quantizing code in an area shape coding unit
806
.
FIG. 25
depicts the 8 directional quantizing code. As can be seen from the figure, the 8 directional quantizing code represents a direction to a next point by a numerical value, which is generally used for representing a digital figure.
At a frame position where a lower layer frame has been coded, superimposing unit
805
outputs a decoded image of the lower layer. At a frame position where the lower layer frame has not been coded, the superimposing unit forms an image by using coded images of preceding and succeeding two coded lower layers of the frame of interest and one upper layer decoded image of the same time point, and outputs the formed image. The image formed here is input to upper layer coding unit
803
and utilized for prediction coding. The method of forming the image in the superimposing unit
805
is as follows.
First, an interpolated image of two lower layers is formed. A decoded image of a lower layer at a time point t is represented as B (x, y, t). Here, x and y are coordinates representing pixel position in a space. When we represent time points of the two lower layers as t
1
and t
2
and the time point for the upper layer as t
3
(where t
1
<t
3
<t
2
), the interpolated image I (x, y, t
3
) at time point t
3
is calculated as follows.
I
(
x, y, t
3
)=[(
t
2
−t
3
)
B
(
x, y, t
1
)+(
t
3
−t
1
)
B
(
x, y, t
2
)]/(
t
2
−t
1
) (1)
Thereafter, a decoded image E of the upper layer is superimposed on the interpolated image I calculated as above. For this purpose, weight information W(x, y, t) for superimposing is formed from area shape information M(x, y, t), and a superimposed image S is obtained in accordance with the following equation.
S
(
x, y, t
)=[1
−W
(
x, y, t
)]
I
(
x, y, t
)+
E
(
x, y, t
)
W
(
x, y, t
) (2)
The area shape information M(x, y, t) is a binary image which assumes the value 1 in the selected area and the value 0 outside the selected area. The image passed through a low pass filter for a plurality of times provides weight information W(x, y, t).
More specifically, the weight information W(x, y, t) assumes the value 1 in the selected area, 0 outside the selected area, and a value between 0 and 1 at a boundary of the selected area. The operation of superimposing unit
805
is as described above.
The coded data coded by lower layer coding unit
804
, upper layer coding unit
803
and area shape coding unit
806
are integrated by a coded data integrating unit, not shown, and transmitted or stored.
The method of decoding in the conventional apparatus will be described in the following. Referring to the right side of
FIG. 26
, in the decoding apparatus, coded data are decomposed by a coded data decomposing unit, not shown into coded data for the lower layer, coded data for the upper layer and the coded data for the area shape. The coded data are decoded by a lower layer decoding unit
808
, an upper layer decoding unit
807
and an area shape decoding unit
809
, as shown in
FIG. 26. A
superimposing unit
810
of the decoding apparatus is similar to superimposing unit
805
of the coding apparatus. Using the lower layer decoded image and the upper layer decoded image, images are superimposed by the same method as described with respect to the coding side. The superimposed motion picture is displayed on a display, and input to upper layer decoding unit
807
to be used for prediction of the upper layer.
Though a decoding apparatus for decoding both the lower and upper layers has been described, in a decoding apparatus having only a unit for decoding the lower layer, upper layer decoding unit
807
and superimposing unit
810
are unnecessary. As a result, part of the coded data can be reproduced in a smaller hardware scale.
In the conventional art, as represented by the equation (1), when an output image is to be obtained from two lower layer decoded images and one upper layer decoded image, interpolation between two lower layers is performed. Accordingly, when a position of the selected area changes with time, there would be a considerable distortion around the selected area, much degrading the image quality.
FIGS. 28A
to
28
C are illustrations of the problem. Referring to
FIG. 28A
, images A and C represent two decoded images of the lower layer, and image B is a decoded image of the upper layer, and the time of display is in the order of A, B and C. Here, selected areas are hatched. In the upper layer, only the selected area is coded, and hence areas outside the selected area are represented by dotted lines. As the selected area moves, an interpolated image obtained from images A and C has two sele
Aono Tomoko
Ito Norio
Katata Hiroyuki
Kusao Hiroshi
Watanabe Shuichi
Britton Howard
Sharp :Kabushiki Kaisha
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