Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1998-02-05
2001-07-31
Powell, Mark R. (Department: 2165)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
Reexamination Certificate
active
06268865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to computer graphics, and more specifically to software and tools for computer-assisted animation.
2. Related Art
Animation has long been an alternative to live-action photography for making films. The look of animation and its ability to exceed the bounds of the physically possible have allowed an art to develop feature films widely regarded as classics. Computer-assisted animation has reduced the labor required to produce an animated feature film and led to a boom in animated films in the 1990s.
Traditional animated films tend to have fairly static backgrounds. Furthermore, the “camera” in the animated film cannot move as freely as the camera in a live-action film, because unrestrained camera movement would require repainting of the background at each frame, a prohibitive expense.
Computer-assisted animation opens up the possibility of making the backgrounds of animated films more dynamic. Various techniques could be employed for this purpose. One possibility would generate backgrounds by means of computer rendering of 3-D objects. The animator creates a mathematical description of the background objects being animated and the light sources illuminating them. A computer program generates from that mathematical description an image which closely resembles a photograph of those objects. The process of generating such an image is referred to as “3-D rendering” or simply “rendering.” Rendering is in a sense a computer simulation of photography. Within this framework, animation is achieved by specifying the movements of mathematically-modelled objects, the light sources illuminating them, and the imaginary camera taking the simulated photographs, and then rendering a suitable number of animation frames. This manner of making animated films was employed, for example, in the feature film Toy Story.
Unfortunately, computer rendering is not very suitable for backgrounds. It is often difficult to model mathematically the objects typically found in backgrounds, such as trees. Furthermore, all computer rendered objects have a distinctive hard-surfaced look, familiar to anyone who has seen Toy Story, which may be perceived as undesirable. This hard-surfaced look arises in part from the fact that the colors of these objects' surfaces are modeled by means of what is called a “texture map,” in which the computer program in effect uses a two-dimensional drawing, generated separately by an artist, and covers the surfaces with that drawing somewhat in the manner of wallpaper to determine the surfaces' colors.
A refinement of computer rendering which has been suggested is to have the artist be able to see instantaneously what the scene will look like as he or she modifies the drawing used for texture mapping. In this way, the artist can more easily tailor that drawing to achieve a desired effect in the final rendered image. The artist is in effect drawing color directly onto the 3-D surface. This refinement is unfortunately both expensive to achieve in terms of computational resources and not a natural way of painting for the artist.
Ideally, an artist would make a two-dimensional drawing of a 3-D scene, and then a computer program would generate views of that 3-D scene from different camera angles using the artist's two-dimensional drawing. The artist would in effect be painting in the familiar way, in two dimensions, and the 3-D effects would be generated by the computer. This is, strictly speaking, impossible, because changes in the camera position could bring into view portions of objects which are occluded in the view painted by the artist, and some additional artist input is consequently required to establish how those occluded areas should look. It would be nonetheless desirable to approximate the ideal as closely as possible.
It is therefore desirable to allow an artist to paint backgrounds of animated films in the familiar manner in which a two-dimensional background is painted (with a computer paint program), and then to have the computer generate automatically views of the 3-D scene which those backgrounds depict from other camera angles.
It is also desirable to have computer's generation of additional views require little additional input from the artist, while still giving the artist the necessary creative control over the final product. Furthermore, it is desirable to have the additional views retain the same painterly appearance as the original view drawn by the artist.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus for painting 3-D objects and producing computer-assisted animated films. After a 3-D model of an object is generated, a view of the object is selected for painting. An artist applies brush strokes to paint the selected view of the object in 2-D space. The brush strokes are mapped onto the surfaces of the object in 3-D space, generating 3-D brush strokes. These 3-D brush strokes are then projected onto the 2-D views in the animation frames, generating projected 2-D brush strokes which are used to paint the views in the animation frames.
Additional views may be selected from the painted views in the animation frames that reveal surfaces that were occluded in the previously selected view. The artist applies additional brush strokes to paint the previously occluded areas. These additional brush strokes are mapped onto the surfaces of the object in 3-D space, and are used together with the brush strokes in the previously selected view to re-generate the painted views in the animation frames.
The present invention also provides methods and apparatus for determining pixel colors used to display brush strokes. When an artist applies 2-D brush strokes to paint a view of an object using a pen or stylus and a graphics tablet, the computer obtains (i) 2-D stroke points by sampling the tracks of the 2-D brush strokes as they are applied by the artist and (ii) a pen pressure at each of the 2-D stroke points. The pixel color of a brush stroke at a pixel may be determined as a function of the size, color, degree of opacity, and degree of “softness” chosen by the artist for the brush stroke, the pen pressures, the pixel location, and a brush profile at the pixel location.
In addition, the present invention provides brush strokes that are “leaf strokes.” When brush strokes are leaf strokes, they are displaced by random amounts in random directions to create a mass of leaves. When an artist paints brush strokes as leaf strokes, he/she paints them as if the leaves are forward-facing him/her. The present invention then displaces the forward-facing leaves by random amounts and rotates them to random angles to produce a volume of leaves.
Additionally, the present invention allows a selective focus which is a painting style where certain painted areas are emphasized and others are de-emphasized. The emphasized or focus areas tend to have more contrast and saturated color, whereas the de-emphasized areas tend to have more muted colors, often transitioning to a background or atmospheric color.
Furthermore, the present invention provides a technique for painting overlapping brush strokes. When two overlapping brush strokes are on the same surface of an object, they are painted in painter's order, which means the brush stroke painted last by an artist is painted on top. When the two overlapping brush strokes are on different surfaces of the object, they are painted in depth order, which means the brush stroke that is closer to the camera is painted on top. When surfaces move relative to the camera, the painting order may change, which may cause a pop. To avoid the popping problem, the two priority orders mentioned above may be blended to provide a smooth transition between them. The present invention also provides a method of painting an arbitrary number of overlapping brush stokes which uses a minimum amount of memory.
REFERENCES:
patent: 5325473 (1994-06-01), Monroe et al.
patent: 5592597 (1997-01-01), Kiss
patent: 5630043 (1997-05-01), Uhlin
patent: 5828819 (1
Daniels Eric
Katanics George T
Lappas Anastasios
Disney Enterprises, Inc.
Irell & Manella LLP
Powell Mark R.
Rossi Jeffrey Allen
LandOfFree
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