Computer graphics processing and selective visual display system – Computer graphics processing – Shape generating
Reexamination Certificate
1999-09-02
2002-06-11
Jankus, Almis R. (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Shape generating
Reexamination Certificate
active
06404434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a curve generating apparatus and method and to a storage medium storing a curve generating program, as well as to a method of setting associate points, suitable for use in a CAD (Computer Aided Design), computer graphics and image edition, for the purpose of enabling edition of curves representing contours of objects contained in images displayed on a computer.
2. Description of the Related Arts
A motion picture or moving image is composed of a plurality of frames of image data each of which contains an object. The profile or contour of such an object is extracted by a technique known as a contour extraction. Such a contour extraction technique is used mainly in the field of image processing technologies such as CAD, graphics, and so forth. Image synthesizing processing is one of such image processing technologies. The image synthesizing processing often requires contour extraction processing which generates a key signal from the contour of an object. When this technique is used, it is important that the key signal is correctly generated to enable generation of contour curves that exactly express the contour. The key signal provides information for scissoring or cutting out a foreground to be synthesized, and is referred to also as a “mask”.
The above-described contour extraction processing includes a processing for forming a contour curve based on detailed information given by an operator in regard to the contour position and direction of an object and, hence, requires an interactive operation. Various types of contour extraction techniques have been known and proposed, such as a technique in which a plurality of points are appointed on the contour of an object so that contours of sections between adjacent points are formed, a technique which operates control points on parametric curves representing a contour outline, and a technique which permits a contour to be directly input by a user by means of a pointing device such as a mouse. For further detail and examples of the contour extraction techniques, a reference be made to Intelligent Scissors for Image Composition, Eric N. Mortensen and William A. Barrett, Computer Graphics Proceedings, Annual Conference Series, 1995, ACM SIGGRAPE, PP. 191-198., as well as to IMAGE CONTOUR DETECTION METHOD (Japanese Unexamined Patent Publication No. 4-152481 and METHOD OF AND APPARATUS FOR FORMING SCISSORING MASK (Japanese Unexamined Patent Publication No. 4-254854).
With the known contour extraction techniques mentioned above, it is necessary that contour curves be formed accurately on each of many elementary pictures or frames that constitute the moving image. For instance, movie or TV motion pictures lasting several seconds require several hundreds of key signals. Thus, the amount of data to be processed is enormous. Therefore, in the field of movies or TV, it is highly desirable that contour curves for the frames constituting a moving picture be generated as accurately as possible with minimal processing, in view of known contour extraction processing which requires much labor and time.
Under these circumstances, a simplified method for generating contour curves has been proposed which is based on an assumption that a contour curve contained in the starting frame of a continuous motion picture is progressively deformed with time into the contour curve in the ending frame of the motion picture. Thus, an intermediate curve which represents the contour curve of the object in a transient frame is generated by interpolation, based on the contour curve contained in the starting frame and the contour curve contained in the ending frame.
More specifically, in accordance with this interpolation method, each of points constituting the starting frame is correlated to corresponding one of points on the contour curve of the ending frame. It is assumed here that a contour contained in the starting frame is represented by a curve “a”, while the contour contained in the ending frame is represented by a curve “b”. The moment at which the starting frame is displayed is “0”, and the moment at which the ending frame is displayed is “1”. Assuming that the contour curve changes with time, it is understood that the contour represented by the curve “a” at the moment “0” has been changed to the curve “b” by the moment “1”. The moment of a transient frame containing the contour to be formed by interpolation is expressed by “T”. The coordinates of a point on the curve “a” is expressed as “A”, while the coordinates of the corresponding point on the curve “b” is expressed by “B”. The coordinates of the corresponding point on the curve in the transient frame is expressed by “C”. With these definitions, the coordinates C is given by the following formula.
C=T·A+(1−T)·B
In the known interpolation techniques, the contour to be contained in an intermediate or transient frame is formed based on points determined by the described interpolation technique.
The contour curve contained in each frame is constituted by a plurality of cubic Bezier curves. The cubic Bezier curve is defined as follows, as described in a literature COMPUTER GRAPHICS PRINCIPLE AND PRACTICE SECOND EDITION in C (Foley, van Dam. Feiner. Hughes, ADDISON WESLEY, 1996, ISBN 0-201-84840-6.
Q
(
t
)
=
(
(
1
-
t
)
3
)
M
+
3
t
(
(
1
-
t
)
2
)
N
+
3
(
t
2
)
(
1
-
t
)
O
+
(
t
3
)
P
(
0
t
1
)
Symbols “M”, “N”, “O” and “P” indicate coordinates of points on a two-dimensional plane. More specifically, “M” and “P” represent coordinates of end points of a line, while “N” and “O” represent coordinates of control points.
FIG. 52
shows an example of a line on a cubic Bezier curve expressed by the formula shown above. Referring to
FIG. 52
, a solid-line curve is the cubic Bezier curve. Points “M” and “P” indicated by solid circles are end points, while “N” and “O” indicated by white blank circles are control points.
In accordance with the aforesaid formula that defines the cubic Bezier curve, the locus of the Bezier curve, i.e., a configuration, can be expressed in terms of the coordinates of the end points “M” and “P”, coordinates of the control points “O” and “N”, and the change of the time “t”.
The unit of the cubic Bezier curve shown in
FIG. 52
constitutes a segment of a curve representing a contour curve. Thus, as shown in
FIG. 53
, a single curve representing a contour curve is composed of a plurality of segments
201
. It will be seen that the train of segments forms the single contour line, with adjoining segments
201
commonly possessing an end point
202
.
In this known contour extraction technique, an intermediate or transient contour is determined by interpolation based on the contour curve of the frame preceding the transient frame and the contour curve of the frame which trails the transient frame. In this technique, therefore, contour curves of different frames are correlated to each other by the end points and control points of each of the segments. This requires that the contour curves of different frames essentially have the same number of segments.
Actually, the number of segments varies in accordance with the degree of complication and size of the contour curve. However, according to the conventional interpolation technique, segments
201
of the same number are employed, even when significant differences in size and shape exist between the contour curve of the starting frame and that of the ending frame significantly differ as shown in FIG.
54
.
Thus, in generating the contour curve of a transient frame by using the conventional interpolation technique, the user is obliged to unnecessarily add end points
203
to the frame containing the contour having fewer segments, in order to equalize the number of the segments
201
of the starting frame and that of the ending frame.
More specifically, referring to
FIG. 54A
, it is assumed that the contour curve of the starting frame has eight segments wit
Kawamura Makoto
Shimada Shigehiro
Cunningham G. F.
Frommer William S.
Frommer & Lawrence & Haug LLP
Jankus Almis R.
Sony Corporation
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