Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1998-04-08
2001-04-03
Vo, Cliff N. (Department: 2772)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
C345S426000, C345S440000
Reexamination Certificate
active
06211882
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to computer graphics imagery, and more specifically, toward the simulation of motion blur in computer generated imagery.
2. Related Art
Individual frames within a sequence of frames recorded using standard video and film cameras often contain noticeable blurring of moving objects. This blurring is rarely noticeable when these frames are played back at the same rate at which they were recorded. A viewer uses the blurriness of the object in the individual frames to make assumptions about its relative velocity and predictions about its position in subsequent frames.
In computer generated animation, on the other hand, a frame is typically generated by sampling an application model at an instant of time. Effectively, the sampling model simulates an instantaneous shutter on a video camera. This form of sampling is satisfactory with scenes of low and moderate action. However, unpleasant stroboscopic effects (e.g., jerkiness) are evident when rapidly moving objects are present. This results since computer generated animation lacks the real-world motion blur of a moving object.
To compensate for these deficiencies, simulated motion blur is used in computer generated imagery to mitigate visually objectionable artifacts that result from the discrete nature of sampling. Motion blur simulations enable an animator to recreate the short-duration exposure intervals of real-world video shutters. Seamless integration of animation and real-world footage can therefore occur. The perceived realism of these integrations will continue to increase as the motion blur simulations improve. Since the simulation of motion blur is computationally expensive, what is needed is an efficient method for handling motion blur in large scenes having arbitrary shaders, textures, transparent objects and surface tessellations (e.g., a polygon mesh).
SUMMARY OF THE INVENTION
In the present invention, motion blur simulation for an exposure interval is provided by analyzing the movement of tessellated representations of surfaces relative to a stationary sampling point on a pixel. The movement of a polygon in the tessellated representation of a surface is approximated by a linear transform of the polygon's vertices. The error of this approximation can be mitigated by increasing the number of linear transforms over the exposure interval.
Polygon movement is analyzed by identifying the intersections between the leading and trailing edges of each individual polygon with the stationary sampling point. These intersection points define the boundaries of segments that indicate the sub-interval of exposure time where the sampling point is inside the polygon. If the sampling point starts inside the polygon or ends up inside the polygon, the segment is bounded by the start or end of the exposure interval, respectively. Each of these segments are placed in a list that is associated with the sampling point.
The list of segments is then sorted to remove portions of segments that are occluded and segments that are completely occluded. The remaining visible surface list contains only segments that are associated with visible polygons. These visible polygons contribute to the shading and texture value that is calculated for the sampling point. Segments associated with transparent polygons also include a transparency chain that identifies polygons that are visible through these transparent polygons.
The polygons in the visible surface list are then grouped together based upon the continuity of time coverage. These groupings allow the reduction of computational complexity when evaluating the shading and texturing functions by sampling the shading and texturing data with less frequency than the geometric intersections would otherwise dictate.
The shading process considers the surface type of the object that the group of polygons represents. For example, the shading sampling rate is kept to a minimum if the surface is uniform. Conversely, the shading sampling rate is increased when the surface of the object is bumped or displacement mapped, highly specular, etc. Computational complexity of the motion-blur system is thereby adopted to the geometric and material properties of the objects that the system processes. Deterministic or stochastic methods can be used to position the sampling points in the temporal domain.
The texture sampling rate and sampling positions are determined independently of the shading process. Textures often include higher frequency patterns and therefore require a higher sampling rate. Since a texture function's look up in a texture file is much less intensive than a shading function's calculation of a reflection model, a minimal penalty in system throughput is incurred. Analytic, deterministic or stochastic methods can be used to identify the position of the texture sampling points in the temporal domain.
After each of the groups of polygon segments in the visible surface list have been processed, the system combines the results based upon the time coverages of each of the groups. The final value yields the shading or texture for that particular sampling point.
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Pearce Andrew P.
Sung Kelvin Hsien Ching
Silicon Graphics Inc.
Sterne Kessler Goldstein & Fox P.L.L.C.
Vo Cliff N.
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