Computer graphics processing and selective visual display system – Computer graphics processing – Graphic manipulation
Reexamination Certificate
1998-06-30
2003-05-27
Padmanabhan, Mano (Department: 2772)
Computer graphics processing and selective visual display system
Computer graphics processing
Graphic manipulation
C345S581000, C345S473000
Reexamination Certificate
active
06570578
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to systems for the production of rendered 2-D images derived from 3-D scene data using computers and more particularly to a system that automates the production of separate sequences of rendered images, known as passes, which are to be used with compositing software to form a completed image or image sequence.
BACKGROUND
Modern computer graphics, as often seen in movies and computer-generated artwork, consist of two-dimensional (2-D) images or image sequences (movies) that are derived from complex 3-D data. The 3-D scene data includes the 3-D coordinates of every object in a scene. Since the images derived from the scene are intended to show a realistic representation of actual 3-D objects, the scene data also includes objects or definitions, called “shaders,” that are used to control rendering related properties of objects and the scene as a whole, for example, surface and volume properties of each object. For instance, the shaders dictate how light is reflected, refracted, and scattered by the objects. Shaders can also be used to control the rendering properties of internal volumes of space (e.g., a 3D object that delimits a puff of smoke) or the entire scene environment, the latter being called an environmental shader.
To make the realistic image, the 3-D scenes are rendered. The process of rendering involves ray-tracing which determines the look of each pixel visible from the camera viewpoint. In ray-tracing, the effects of occultation and diffuse and specular reflection, refraction, and diffusion of light by the various objects and volumes in the scene are determined. Ray tracing not only accounts for primary effects which are the reflections, refractions, and diffusions of light coming directly from the light sources, but also for secondary reflections. The latter are effects when primary light from other objects illuminates or passes through an object or volume. These secondary effects can involve multiple reflections between the original light source and the camera so that, considering that rays must be traced for every pixel in a scene and considering that some shaders involve complex numerical algorithms, the process of rendering is extremely time consuming for current computer technology.
To speed up the process of authoring such images and image-sequences (the latter corresponding to animation as opposed to still images), graphic artists generate images that include particular features of the final image which, when combined (or perhaps with others if not all essential passes are generated), form a complete image or image sequence. For example, a so-called matte pass shows only the outline of a first object. That is, it shows only the parts of the objects behind the first object that are not occulted by it. In such a pass, the first object might appear solid white with no surface features at all. Another pass could be a shadow pass showing only the shadow created by an object or group of objects. These passes are combined to form a final image in a process called compositing.
Breaking a final rendered image into these passes and subsequently compositing the passes allows an intermediate process, prior to compositing, where specific features of the final image may be modified by editing the pass images using pixel editing software. Various features may be tweaked without going back to the original 3-D models. For example, the darkness or hue of a shadow may be tweaked by editing a shadow pass image. The subsequent process of compositing is performed quickly to provide a full final image. The artist can then return to the passes to make further changes and again re-composite to see the results. Since the compositing operation, which starts with the passes, runs very quickly, this process of tweaking pixel properties can be done iteratively and quickly to refine the images. The alternative, for the example changing the shadow, would require changing the lighting in the 3-D scene data to produce the desired effect. This would require a re-rendering of the entire scene, which takes a long time.
The following are various types of passes that can be created. A beauty pass is a full rendering of a selected object of a group of objects. The beauty pass renders the entire scene with no modifications. A matte pass shows an outline of a selected object with the surface of the object appearing uniformly which, so that it demarcates a silhouette of the object. The background and non-selected objects are invisible in the matte pass. A shadow pass shows only a shadow generated by an object with the object generating the shadow and other objects (as well as the background) not appearing upon rendering. A highlight pass shows only the surfaces of selected objects that appear bright due to specular reflection with the rest of the scene flagged as invisible. A transparency pass is a beauty pass of one or more transparent selected objects with the rest of the scene flagged as invisible. A refraction pass shows only light refracted through one or more selected objects with the rest of the scene flagged as invisible. This list is by no means exhaustive and is provided by way of example to facilitate the purposes of this disclosure.
Obviously, only some modifications can be made efficiently by pixel-editing the pass images. Certain modifications are only efficiently done by returning to the 3-D scene. For example, if the shape of an object must be changed, the complex modifications that have to implemented such as highlighting, shading, and the details of the shape, require editing of the 3-D model of the object defined in the scene.
Referring to
FIG. 1
, the process of generating passes after creating or editing the step of three-dimensional scene
10
involves several steps. First, a number of copies of the scene are made
15
a
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15
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. Then each copy is edited
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a
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20
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to modify the properties as appropriate for the respective pass to be generated. For example, to generate the matte pass for a first object, the user sets the surface shaders of the object such that the object will appear totally white when this version of the scene is rendered. The same is done for each object for which a matte pass is to be generated. For another example, to generate a beauty pass for the first object, another copy of the scene is made and modified to set the shaders of all but the first object transparent or “zero-alpha.” Thus, each time a scene is edited, a copy is made for each pass and pass-specific parameters of the copy set to generate each particular pass. This is because changes in the 3-D scene may (and probably do) affect every single pass. Next, each edited copy is rendered to create the particular pass. The user works with the passes in step
45
and may decide to edit the 3-D scene. The process of generating a new set of passes is the same as before. The author returns to the step of editing the scene
10
and follows the same procedure to produce a new set of passes. This process of editing copies of scenes to generate passes may be tedious and time consuming. The tasks indicated by dark-bordered boxes are labor-intensive activities. Each must be repeated every time the scene is edited.
SUMMARY OF THE INVENTION
The invention is a system for method for automating the process of creating pass-definition (passes) from a three-dimensional scene. The invention allows a user to define, in a separate step, a series of pass definitions. Each pass definition includes properties that override those defined in the scene. When a given pass definition is applied to the 3-D scene, the system automatically changes the scene according to the pass definition. Once the pass is set as active, the scene is rendered to produce a respective pass-image or image sequence, or, simply, “pass’.
Consider, for example, the steps for making the matte pass. In the invention, the definition of a matte pass is broken out as a separate process. The properties may be assigned to objects through object-groupings called partitions. Thus, the pass definition may identify a p
Krattli Jean-Marc
Smirnov Alexis
Avid Technology Inc.
Gordon Peter J.
Padmanabhan Mano
LandOfFree
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