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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to the field of machine generation of animation and,
more particularly, to a method and apparatus for generating sequences of
frames on a two-dimensional screen that are representative of
three-dimensional animated figures.
Animated films are in widespread use for educational and entertainment
purposes. Animated films of reasonably high quality have traditionally
been very expensive to make. The initial creative work includes generation
of a basic story, a sound track, and basic character designs. Typically, a
schedule is generated which describes the movements and timings of each
scene to be produced, and layout sketches and "key" drawings are made
which define the overall design of each scene. It has been generally
observed that at this point most of the creative design work has already
been done. The so-called "key" drawings or frames are still frames which
show extremes of action. In the traditional animation procedure, people
known as "in-betweeners" are employed to sketch frames which fill in the
action between key frames. After in-betweens are sketched by hand, the
hand-drawn pictures are typically transferred onto celluloid-acetate
sheets and are then painted in by hand. Much labor is involved in
obtaining the in-betweens, which typically comprise the majority of frames
of the final work product. These tasks render the production of animated
films an extremely expensive proposition. An advantage of the traditional
animation process, however, is that the animator has virtually complete
artistic freedom and control over the resulting film; i.e. anything that
is drawn can be made to move in a desired fashion so natural-looking
motion can generally be achieved.
In recent years, the field of machine generation of animation has made
great strides. Advanced computer graphics techniques have improved the
speed and quality of computer-generated animation. Computers can aid
artistic animators in many ways, including automatic generation of
in-between frames by interpolation of lines appearing in successive key
frames. A technique of this type is described, for example, in an article
entitled "Towards a Computer Animating Production Tool" by N. Burtnyk and
M. Wein which appeared in the proceedings of Eurocomp Conference, Brunel -
United Kingdom, May 1974.
It is known in the computer graphics art that three-dimensional
representation of animated figures can be stored as a set of three
dimensional points, and appropriate transformations can be used to
automatically compute the projection of the three-dimensional figures onto
a two dimensional surface, so that two dimensional computer generated
animation images can be presented on a conventional two-dimensional
screen. Three dimensional figures have also been represented in joint and
limb configuration.
Representative prior art patents relating to techniques such as
computer-generation of in-between frames and three-dimensional animation
are as follows: U.S. Pat. Nos. 3,364,382; 3,523,389; 3,585,628; 3,603,964;
3,700,792; 3,723,803; 3,747,087; 3,792,243; 3,883,861; 3,917,955;
3,885,096; 4,017,680; 4,127,849; 4,189,743; 4,189,744; 4,200,867;
4,213,189.
As above-stated, the automatic machine generation of in-between frames can
greatly reduce the amount of time and effort that is necessary to generate
a series of animated frames. Particularly when dealing with
three-dimensional animation, however, the automatic generation of
in-between frames can tend to result in unnatural motion of the three
dimensional figures.
It is among the objects of the present invention to provide a method and
apparatus for generating frames of three-dimensional animated sequences
which have natural-looking motion. It is a further object to provide an
animator with a high degree of flexibility in obtaining the desired
appearance of motion of figures with minimal labor.
SUMMARY OF THE INVENTION
The present invention is directed to an improved method and apparatus for
generating a sequence of video frames representational of
three-dimensional animation. In accordance with the method of the
invention, a plurality of key frames are stored, each key frame including
a common figure having one or more joints, and each joint having
associated therewith a set of vectors defining a limb. Each joint is
defined in each frame by operator-controllable parameters which determine
the three-dimensional position, rotational orientation, and scale factors
of a local coordinate system in which the limb vectors are placed. A
plurality of in-between frames are generated, the in-between frames
including the common figure having one or more joints and limbs
corresponding to the joints and limbs of the common figure in the key
frames. The parameters of the joints of the in-between frames are obtained
by interpolating, in three dimensions, the position, rotational
orientation, and scale factors of the corresponding joints of the key
frames.
In the preferred embodiment of the invention, the joints of each figure are
arranged in hierarchical order, and the positional coordinates and
rotational orientations of the local coordinate system for a particular
joint are determined with respect to the local coordinate system of the
next higher joint in the hierarchy. Also, in accordance with the preferred
embodiment, the operator can control the interpolation during display of
the in-between frames, so as to change the motion of a figure limb.
Further features and advantages of the invention will become more apparent
from the following detailed description when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an apparatus in accordance with an embodiment
of the invention, and which can be used to practice the method of the
invention.
FIG. 2 is a flow diagram which describes the generalized procedure for
producing three-dimensional animation on a two-dimensional screen,
including the technique of the invention.
FIG. 3 is a flow diagram of the routine for forming skeleton files for a
sequence of animation to be generated.
FIG. 4, which includes FIGS. 4A and 4B, illustrates a joint and limb in a
local coordinate system, and shows the manner in which a joint and limb
are represented and can be manipulated.
FIG. 5 is a flow diagram which illustrates the routine for displaying
frames of figures represented by joints and limbs in three dimensions on a
two-dimensional display.
FIG. 6 is a flow diagram of the routine for forming a frame, such as the
key frame.
FIG. 7 is a flow diagram of the routine for generating in-between frames.
FIG. 8 is a flow diagram of a routine for modifying the motion of a limb
during display.
FIG. 9 shows an interpolation curve and a modified interpolation curve.
FIG. 10 is a flow diagram of the routine for modifying the interpolation
curves.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is shown a block diagram of an apparatus 10 in
accordance with an embodiment of the invention and which can be used to
practice the method of the invention. An operator 15, who is typically,
but not necessarily, an animator of some artistic ability, works at a
console which includes the devices illustrated within the dashed enclosure
20. In the present embodiment, the console includes three types of input
devices whereby the animator can input information to the apparatus 10,
viz. a data tablet 21, a keyboard 22, joysticks 23 and monitors on which
information is displayed, viz. monochrome display 23 and optional color
display 25.
The devices in the console 20 are coupled via a bus 30A to control
circuitry 30. In the present embodiment the novel functions of control
circuitry 30 are implemented by an appropriately programmed general
purpose digital computer, for example the model VAX 11/780 or the model
PDP-11/45 manufactured by Digital Equipment Corp. of Maynard, Mass.
However, it will be understood that alternate means, such as a special
purpose computer or other suitable circuitry having logic and storage
capabilities could be utilized to achieve the desired functions. In
conjunction with the general purpose digital computer 30 there is provided
memory which includes fast access bulk storage such as disk memory 52, and
random access storage labelled RAM 53. Typically, at least a portion of
the random access memory will be included within the general purpose
computer 30, and it will be understood that the amount and type of each
storage medium or alternative storage can be selected by one skilled in
the art.
An optional frame storage means 60 is provided and is coupled, inter alia,
to the control circuitry 30 and to the color monitor 25. The frame storage
means is of the type known as a "frame buffer" manufactured and sold by
Genisco Computer Company of California. Essentially, the frame buffer 60
is an addressable digital memory which stores a frame of video
information. The frame buffer 60 is coupled to the control circuitry 30
via the bus 30A so that the control circuitry 30A can typically be
utilized to address any desired pixel in the frame buffer, for example to
interrogate or read the pixel value contained therein or to write in a new
pixel value at any point.
In the present embodiment of the invention, it is convenient although not
required, to employ a commercially available processor for performing
certain matrix transformations and display tasks which could alternatively
be performed by general purpose processing and display circuitry. In
particular, a three-dimensional line drawing display system with
coordinate transformation and clipping hardware is collectively referred
to as the line drawing system 70, and includes processor 71 and line
drawing display 72. A suitable vector processing and display system is the
Evans and Sutherland Company "Multi Picture System". A raster-based system
which performs similar functions is described in an article entitled
"Coprocessing to Ease The Graphics Burden" which appeared in the July,
1982 issue of "Computer Design". The system 70 is coupled via the bus 30A
to the other equipment. A video tape recorder 55 and a television camera
65, may also be provided in the system.
Referring to FIG. 2, there is shown a generalized flow diagram of a typical
operational procedure for generating a sequence of frames of three
dimensional animated scenes for display on a two-dimensional screen. It
will be understood, however, that variations in this typical procedure can
be employed, consistent with the principles of the invention, depending,
inter alia, upon the type of animation to be produced, the source of
component figures, and operator preference.
The block 211 represents the inputting and storage of limb files, which, if
already existing, can be keyed in via the keyboard 22, or can be drawn in
via the data tablet 21, or by using the joysticks and cursor control. In
the present embodiment, each limb is represented, in known fashion, as a
set of vectors in three dimensions which define the limb shapes to be used
on the figures in the sequence of animation. The form of representing the
vectors and limbs is treated hereinbelow. It should be noted that this
part of the procedure is not strictly necessary to perform at this time
(since limbs can be produced after the skeleton of joints is formulated,
as described hereinbelow), but in many practical situations one can
utilize previously stored three dimensional vector representations of
limbs available from a "limb library". Also, it is usually convenient to
generate limbs beforehand for use during the sequence of animation to be
generated, it being understood that certain limbs can be utilized a number
of times in the various figures of the animation. The representative limb
to the left of block 211 is a simple robot foot.
The block 212 represents the formation of a skeleton file for each figure
in the sequence of animation to be generated. As previously indicated,
each figure includes one or more joints, and each joint has associated
therewith a limb. Each joint is defined in each frame by
operator-controllable parameters which determine the three-dimensional
position, rotational orientation, and scale factors of a local coordinate
system in which the limb vectors are placed. The joints of each figure are
arranged in a hierarchical order, and the positional coordinates and
rotational orientations of the local coordinate system for a particular
joint are determined with respect to the local coordinate system of the
next higher joint in the hierarchy. The information defining these
parameters for each joint will be described in further detail hereinbelow.
A simplified skeleton figure is illustrated to the left of block 212 of
FIG. 2. In this sketch, the joints are represented by small circles and,
for ease of illustration, straight lines are shown as connecting each
joint to its "parent" joint; i.e., the joint of next highest priority in
the joint hierarchy. In the sketch, the joint J1 is the highest priority
joint for the figure, so the motion, rotation, or scaling of the joint
parameters for J1 will serve to move, rotate, and scale the entire figure
in the world coordinate system. The joints J2, connected to joint J1 as
their parent, are the next lower order joints in the joint hierarchy.
There are three such child joints J2, designated as J2A, J2B, and J2C.
Also, the joint J2A is a parent of three more child joints designated as
J3A, J3B, and J3C.
The routine for forming and storing the figure skeletons is shown in FIG.
3. The block 311 represents the identification of the skeleton file for
the particular figure whose skeleton is to be generated. A joint is
identified to be input (block 312) and its connection in the hierarchy is
indicated, e.g., by identifying its parent joint. If desired, the skeleton
can be displayed during this operation (see display routine of FIG. 7).
Initial x, y and z coordinates of the joint position are stored, as
represented by the block 313. Initial rotational orientation values and
scaling factor values can then also be stored (for example, zero degrees
rotation and unity scaling factor, as initial values) as represented by
the block 314. The meaning and purpose of these values are described
further hereinbelow. The next joint of the figure can then be added
(re-entry to block 312). Additional figure skeletons can be formed and
stored by repeating the procedure.
Referring again to FIG. 2, the block 213 represents the portion of the
generalized procedure wherein individual figures of a frame are formed, so
that the desired poses are obtained for the key frames of the animation
sequence to be generated. This routine is described in conjunction with
FIG. 6. The figure sketched to the left of block 213 is useful for initial
illustration of how the limbs, designated with notation similar to the
joints with which they are respectively associated, except that an L is
used instead of a J, are stored in conjunction with the skeleton file.
Thus, each joint of the skeleton file for a figure has stored in
conjunction therewith a limb file (or identification of the limb file) for
the particular limb that is selected by the operator for use at a
particular joint position of the figure.
The key frames are stored (block 214) and, under operator control,
in-between frames can be automatically generated (block 215) in accordance
with the principles of the invention, and as described in conjunction with
the routine of FIG. 7. During or after such generation of in-betweens, the
sequence of animated frames can be displayed, and modifications to the
sequence can be implemented, as represented by block 216 and as described
in conjunction with the routine of FIG. 8. The final sequence of frames
can then be stored (block 218) and rendered (block 219) by providing
appropriate surface characteristics to the wire frame type structures that
result from the described procedure. Appropriate color rendering can also
be implemented, as is known in the art. One or more frame buffers (e.g.
60) and color monitor 25 can be used toward this end. In this regard,
reference can again be made to the book "Principles of Interactive
Computer Graphics", as well as to U.S. Pat. Nos. 4,189,743 and 4,189,744,
assigned to the same assignee as the present application, and to the
patents listed in the background portion hereof.
The position, orientation, and scaling factors of the set of local
coordinates for a particular joint is defined with respect to the
coordinate axes of the next higher priority joint in the hierarchy of
joints. In particular, a parametric matrix defining the local coordinate
space is given by:
##EQU1##
The values m.sub.x, m.sub.y and m.sub.z respectively represent the x, y,
and z position or "move" coordinates of the origin of the local coordinate
system (i.e., the point at which the particular joint is defined as being
located) with respect to either the world coordinate system (for the
highest priority joint) or to the local coordinate system of the next
higher priority joint in the hierarchy of joints. The values r.sub.x,
r.sub.y, and r.sub.z represent respective rotational angles around the x,
y, and z coordinate axes of the local coordinate system (again, with
respect to the orientations of the coordinate axes of the next higher
priority joint coordinate system). The values s.sub.x, s.sub.y, and
s.sub.z are scaling factors for the x, y and z directions of the local
coordinate system. A value of unity is used to represent the normal scale
factor in each dimension, and higher or lower numbers can be used to
stretch or compress the limb associated with the local coordinate system
in any direction.
FIGS. 4A and 4B are useful in understanding the manner in which the joints
and limbs are represented and manipulated. In FIG. 4A, there is shown the
coordinate axes for an exemplary joint, J.sub.i, and a limb, L.sub.i,
(shown in dashed line) of vectors associated with the joint. The matrix
values for the joint J.sub.i is as follows:
##EQU2##
As seen in FIG. 4A, the origin of the local coordinate system for J.sub.i
is at the point (10, 10, 10) in the main or "world" coordinate system
(which, in this example, is the coordinate system of next higher priority
in the hierarchy). Also, the x, y, and z axes are aligned with the axes of
the world coordinate system, so the relative rotation angles in the second
row of the matrix are all 0.degree.. Finally, it is assumed that, for this
example, the scale factors for the frame are all unity. The limb L.sub.i
associated with the exemplary joint is represented by the following vector
list:
[(1,1,0), (-1,1,0), (-1,-1,0), (1,-1,0), (1,-1,4)-------]
The list sets forth the vertices of the limb as defined in the local
coordinate system (FIG. 4). A comma separates the points which are joined
by lines, so some individual points may be listed more than once.
Reference can now be made to FIG. 4B which represents the same joint
J.sub.i and limb L.sub.i, but with the position, orientation, and size and
shape of the limb being different by virtue of modifications in the matrix
values of the examplary joint. In particular, the matrix for the joint of
FIG. 4B is as follows:
##EQU3##
In this case, the origin of the local coordinate axes (i.e., the joint
position) is seen to be at the coordinates (10, 15, 10), which correspond
to the values in the first row of the matrix. Also, it is seen that the y,
z axes are rotated by 45.degree. around the x axis as compared to the
orientations of the y, z axes in the parent "world" coordinate system.
Accordingly, the second row of values has a 45.degree. rotational angle
indicated in the x column, and 0.degree. rotational angles indicated for
rotation around the y and z axes. Regarding scaling, the limb of FIG. 4A
is seen to be doubled in length or "stretched" along the z axis (only).
Thus a scale factor of 2 is indicated in the z column of the third row of
the matrix. It will be understood that in the present embodiment the
representations of the limb vectors can remain fixed during a sequence of
animation, with the changes in position, orientation, and size and shape
of the limb being achieved by modification of the parametric matrix of the
joint with which the limb is associated. Also, when a modification in a
parameter of a joint is implemented, it is seen that the limbs of all
lower priority joints are effectively modified along with their parent
joints.
It is known in the computer graphics art that geometric transformations can
be used in generating an image on a two-dimensional screen of
three-dimensional scenes. Reference can be made, for example, to the book,
"Principles of Interactive Computer Graphics," referred to hereinabove. In
the present invention, matrix transformations are employed to transform
the limb vectors in a given local coordinate system into equivalent
vectors in the joint coordinate system of next highest priority. The
procedure is repeated for successively higher priority joint coordinate
systems until the limb vectors are expressed in terms of the world
coordinate system. Finally, a perspective transformation is used to
project the three-dimensional scene onto a two-dimensional surface (e.g.
corresponding to the display screen surface). This perspective
transformation depends upon the location, rotational angle and viewing
angle of an imaginary camera whose position and other parameters are
variable under operator control, such as by manipulating one of the joy
sticks.
It is known that if a geometric transformation does not deform an object it
transforms, then it must be decomposable into primitive translation and
rotation transformations. As described, the inclusion of a scaling
transformation allows stretching and contraction of limbs during motion.
The matrix transformation which translates a point (x,y,z) to a new point
(x',y',z') is known to be:
##EQU4##
where m.sub.x, m.sub.y and m.sub.z are the components of the translation
or move in the x, y and z directions respectively, and the 1 in each
fourth column is the homogeneous coordinate.
Rotation about the z axis (for example), through an angle .theta. can be
achieved with the following transformation:
##EQU5##
It can be noted that this transformation matrix affects only the values of
the x and y coordinates. Similarly derived transformation matrices can be
set forth for rotation about the x and y coordinate axes.
A scaling transformation, for use to scale dimensions in each coordinate
direction, is as follows:
##EQU6##
where s.sub.x, s.sub.y, and s.sub.z are, respectively, the scaling factors
in the x, y and z directions.
If the translation, composite rotation, and scaling matrices are
represented by [M], [R], and [S], respectively, a composite transformation
matrix [T], can be set forth as:
[T]=[M][R][S]
This composite transformation matrix corresponds to the composite parameter
matrix for the joint local coordinate system first set forth above at (1).
To transform the vectors of a limb associated with a joint J.sub.n which
has respective parent, grandparent, etc. joints J.sub.n-1, J.sub.n-2,
etc., into a main or world coordinates system (represented as J.sub.0),
the overall transformation matrix, [T.sub.n+0 ] can be represented as the
concatenation of the various local matrix transformations, as follows:
[T.sub.n.fwdarw.0 ]=[T.sub.1 ][T.sub.2 ]-----[T.sub.n-1 ][T.sub.n ]
where the subscripts of the transforms and the joints correspond.
Once expressed in terms of the world coordinate system, a known viewing
transformation [V] can be used to convert points in camera two-dimensional
perspective coordinate system (x.sub.c, y.sub.c) in accordance with:
[x.sub.c y.sub.c z.sub.c w.sub.c ]=[x.sub.w y.sub.w z.sub.w 1][V]
where [V] is known to be a composite viewing transformation that is built
up from several translations and rotations that are determined from the
viewing parameters, and w.sub.c is the resulting homogeneous coordinate.
Reference can again be made, for example, to the previously cited book and
patents. The transformation to the appropriate two-dimensional coordinates
(x,y) is thereby seen to be achieved by multiplying the points in the
world coordinate system by the viewing transformation and subsequent
division by the homogeneous coordinate.
Referring to FIG. 5, there is shown a flow diagram of a routine for
controlling the display of the three-dimensional images stored in memory
in joint and limb format. In general, the routine involves the obtainment
of the two-dimensional (x,y) coordinates of the figures to be displayed
(for each frame) by concatenation of matrix transforms, as previously
described, to obtain the two-dimensional projections of the limb vectors
in the main world coordinate system as viewed with an operator-selected
imaginary camera. The two-dimensional projections are displayed on the
line drawing display 72 of system 70. The set-up and multiplication of the
matrices can be implemented in the general purpose processor 30 but, more
preferably, is achieved by providing the matrix information to the system
70 which is well suited for this purpose.
In FIG. 5, the block 511 represents the reading of the stored parametric
matrix of the next highest priority joint (beginning with the highest
priority joint). In the present embodiment, the joints are processed in
order, from highest priority to lowest priority, as this facilitates the
computations. The block 512 is then entered, this block representing the
multiplication of the matrix for the current joint by the concatenation of
matrix transformations for the previous joints of higher priority than the
joint currently being processed and then by the viewing transformation,
consistent with relationships just set forth above. The latest
concatenation of matrix transformation is stored, as represented by the
block 513. It will be understood that when the next lower priority joint
is processed, the stored concatenation of matrix transformations can be
used again so as to reduce the necessary computation.
A determination is next made (decision diamond 514), as to which display
mode is active. In the present embodiment, the operator can elect to
display either limbs which comprise the actual figures, or skeletons which
are useful in visualizing the positions of the joints and the statuses of
the coordinate axes defined by the joints. If the figure limbs themselves
are to be displayed, the block 515 is entered, this block representing the
reading of the limb vector coordinates associated with the current joint,
and the multiplication of each point by the concatenated matrix
transformation. If the figure skeletons are to be displayed, a basic
orthogonal coordinate system representation (i.e., three mutually
orthogonal lines), can be multiplied by the concatenated matrix
transformation, so as to obtain properly oriented and scaled local
coordinate axes representation at each joint position, as shown in the
small sketch near block 516. The block 521 is then entered (from block 515
or 516), this block representing the storage and display of results on
line drawing display 72 of system 70. A determination is then made
(diamond 522) as to whether or not the last joint in the frame has been
processed. If not, the block 511 is reentered. When all joints have been
processed, display of the frame can be repeated, or the next frame
displayed, depending upon the function being performed.
Referring to FIG. 6, there is shown a flow diagram of routine for forming
and modifying the key frames, as represented generally by the block 213 of
FIG. 2. The key frame to be formed is identified (block 611), and the
first figure to be placed in the scene represented by the key frame being
formed is accessed by calling up its skeleton file (and the limb file
which was previously stored in conjunction with the skeleton file), as
represented by the block 612. The joint (and accompanying limb) to be
manipulated is then identified, as represented by the block 613. As
described hereinabove, the display of the figure can be implemented, at
the operator's option, either in terms of a skeleton of joints or as a
full figure of limbs. A cursor can be conventionally employed to identify
the joint whose accompanying limb is to be manipulated. Alternatively, the
limb associated with the joint to be manipulated can be identified with
the cursor. The parameter to be modified, i.e. motion, rotation, or
scaling, is identified, as represented by the block 614. In an embodiment
of the present invention, a keyboard control key is utilized to identify
the selected parameter, and a joystick is thereby placed in a mode to
control the selected parameter. However, it will be understood that, if
desired, separate joysticks can be provided for each parameter. In either
event, motion of the joystick is effective to modify the x, y and z
components of the selected row of the above-described parametric matrix
(which, in turn, causes the displayed limb appearance to change
accordingly, consistent with the described display routine). The
modification of the values in the selected row of the joint's parametric
matrix is represented by the block 615. The technique is repeated for all
joints to be manipulated (block 616), and the modified figure is stored in
conjunction with the key frame indication (block 617). The procedure can
then be repeated, if desired, to add figures to the scene of the key frame
and manipulate the figures as desired (block 618). In this manner, the
individual key frames can be formulated and stored.
FIG. 7 illustrates the routine of the present embodiment for generating
in-between frames. It is assumed that for a sequence of frames to be
in-betweened, there are a number of key frame poses for each of one or
more figures, and the object of the in-between generation is to produce
natural or other desired motion of figures in the sequence. The block 711
represents selection of the sequence of frames to be in-betweened. The
joint to be treated is selected, (block 712), and the next parameter to be
interpolated is selected, as represented by the block 713. Each of the
motion, rotation, and scaling parameters of the transformation matrices of
the current joint are interpolated in the present embodiment, and this is
done for each of the x, y and z components. The x, y or z component is
selected (block 721). Next, an interpolation curve is fit between the
selected parameter values for the selected component. In an operational
embodiment hereof, a cubic curve was fit through the points in a standard
in-betweening plot of frame number versus the parameter being interpolated
(see e.g. FIG. 10). Block 723 is then entered, this block representing the
storage of values from the interpolation curve in the transformation
matrices of the frames being in-betweened. In particular, the selected one
of the nine values in the parametric matrix described above for each joint
is stored for each of the in-between frames, based on the value of such
parameter component taken from the cubic interpolation curve.
Determination is then made as to whether or not all three components have
been considered (diamond 724). If not, the loop 731 continues. When
complete, a determination is made (diamond 725), as to whether or not all
parameters have been processed. If not, the loop 732 continues. When all
parameters have been processed, determination is made (diamond 726), as to
whether or not all joints for all figures in the sequence of frames have
been processed. If not, the loop 733 is continued until all joints have
been processed, as described. In this manner, the in-between frames are
formed and stored. It can be noted, as represented by the block 729, that
the limbs associated with each joint are obtained in conjunction with the
joint in each frame of the sequence, the motion of the limb being
completely defined as described above, by the matrix transformation values
of the associated joint.
In accordance with a feature of the invention, when a generated sequence of
animation is displayed, the operator can modify the motion of a limb
during a continuous display of the sequence. This is achieved by accessing
the parametric transformation matrix for the joint associated with the
selected limb, and substituting, during display of the sequence, parameter
components which are selected by the operator (preferably, by manipulation
of a joystick), and are used in place of the previously stored parameter
components of the joint during the frame sequence in question. In the
present embodiment, at each frame of a sequence being displayed, the x, y
and z components of a selected parameter (move, rotation or scale factor)
of a selected joint are incremented by an amount which is proportional to
the operator selection of x, y and z values using the joystick. The
routine for effecting this feature is illustrated in FIG. 8.
The frame sequence to be reviewed and modified is identified (block 811).
The joint and parameter to be modified are selected by the operator, as
represented by block 812. As frames are displayed, the operator
manipulates the joystick to indicate increments in the x, y and z
components of the selected parameter of the selected joint. The sensing of
these increments is represented by the block 821. The matrix parameter
components are modified in accordance with the sensed increments, as
represented by the block 822. A frame is then displayed (block 823), in
accordance with the display routine of FIG. 5. Determination is then made
(diamond 824) as to whether or not the full sequence of frames has been
displayed. If not, the next frame of the sequence is processed (block 825)
by reentering block 821, and the loop is continued as each frame, with the
modified limb, is displayed. The procedure can then be performed for any
selected joint or parameter, under operator control. Also, it will be
understood that both the old and new sequences of matrices for the
selected joint can be saved so that the operator can decide what is to be
used in the finally compiled frame sequence.
The motion of a limb during sequence of frames can also be varied by
specific modification of the interpolation curve for each component of
each parameter of transformation matrix of the joint associated with the
particular limb. For example, in the present embodiment, the interpolation
curve can be displayed, such as in FIG. 10 which shows a curve for the x
component of position ("move") fitted to four key frames. The computed
in-between frame x positions are shown as hollow dots and the key frame
positions are shown as solid dots. The solid curve is the original
interpolation curve, and the dashed line curve represents an
operator-modified curve which can be input, for example, via the data
tablet. Preferably, the old and new curves are both saved so that the
motion of a particular limb can be modified until the operator is
satisfied. It will be understood that similar operation can be performed
for the x, y and z components of rotational orientation and scale factor,
as well as for the other components of position.
FIG. 9 illustrates the routine for accessing and modifying the
interpolation curve as described. The operator first indicates the
sequence of frames to be reviewed (block 911). The joint and parameter
component to be modified are then identified (block 912) and the
corresponding interpolation curve (see FIG. 7 routine) is displayed, as
represented by the block 913. The operator can then draw the modified
interpolation curve (or input the information in any other desired way),
as represented by the block 914. The modified curve values can then be
stored, and the sequence of frames reviewed with the new curve.
The invention has been described with reference to a particular embodiment,
but variations within the spirit and scope of the invention will occur to
those skilled in the art. For example, it will be understood that key
frames can be defined in terms of individual figures which have key poses
in those frames, so that different frames will be considered key frames
with regard to different figures. Also, the invention is not dependent
upon any particular type of coordinate transformations or viewing
transformations being used, and additional techniques, such as for
handling clipping can be implemented, as is known in the art. While the
invention is described in terms of a monochrome system, it has application
to color systems as well. It will also be understood that special purpose
hardware implementations of various described portions of th | | |
