Soft shadows for cinematic lighting for computer graphics

• US 20080174600A1
• Filed: 02/16/2007
• Published: 07/24/2008
• Est. Priority Date: 01/23/2007
• Status: Active Grant

• Current Assignee: Pacific Data Images LLC (Comcast Corporation)
• Original Assignee: DreamWorks Animation LLC (Comcast Corporation)
• Inventors: Xie, Feng
• Granted Patent: US 7,969,438 B2
• Time in Patent Office: Days
• US Class Current: 345/426
• CPC Class Codes: G06T 15/60 Shadow generation
• CPC Class Codes: G06T 2215/12 Shadow map, environment map

Abstract

A method and apparatus for high quality soft shadows for area lights in cinematic lighting for use in computer graphics, such as computer enabled animation. The method is an extension of traditional shadow maps, so it has the advantage of image based shadow methods; the complexity of the present method is independent of geometric complexity. It uses multilayer translucent shadow maps, which can be used to produce high quality soft shadows for scenes with extremely complex geometry, fur, and volume objects. Instead of the traditional sampling and filtering of shadow maps, the present method computes the shadow factor by ray tracing the multilayer translucent shadow map. The result is soft edged shadows of quality similar to that achieved by conventional stochastic ray tracing, but at much lower computational cost.

Claims

1. A computer enabled method of animation, comprising the acts of:

providing an image depicting at least one object;

storing in a memory a plurality of depth values of each pixel of the image;

tracing a projected light ray against each of the plurality of depth values; and

performing an intersection test of each traced light ray to define at least one shadow in the image, as cast by the light ray.

2. The method of claim 1, further comprising the acts of sampling and filtering the image with the defined shadow.

3. The method of claim 1, wherein the act of storing comprises:

providing a scan line renderer; and

in the scan line renderer, providing a list of a plurality of samples for each pixel representing the depth values.

4. The method of claim 3, further comprising the act of inserting a sample into the list when the image is rasterized.

5. The method of claim 1, wherein the act of performing the intersection test comprises:

transforming the light ray to a ray in camera space of the image;

clipping the camera space ray;

projecting the clipped camera space ray to a screen space of the image; and

ray tracing the resulting screen space ray against the stored plurality of depth values.

6. The method of claim 1, wherein the object is translucent, and further comprising the acts of:

projecting a light ray to each pixel of the image;

storing a position and opacity of surfaces or volume samples intersected by the projected light ray for each pixel; and

determining visibility changes of the projected light ray.

7. The method of claim 1, wherein the object is translucent, and further comprising the acts of:

projecting a light ray to each pixel;

storing a depth and opacity of selected points intersected by the projected light ray for each pixel; and

computing opacity for any depth along a path of the projected light ray using an interpolation of values of the stored depth and opacity.

8. The method of claim 7, wherein for each pixel there is provided a list of layers, each layer having a depth, an accumulated opacity, and a number of samples.

9. The method of claim 8, further comprising the acts of:

storing a number of samples between each pair of the selected points; and

when the accumulated opacity is zero, resetting it to a value of 1.

10. The method of claim 8, wherein the projected light rays emanate from an area light source, and further comprising the act of determining the accumulated opacity along a length of each of the plurality of projected light rays.

11. The method of claim 1, further comprising the act of:

moving a source of the projected light rays further from the object, whereby the object is not clipped by the projected light ray.

12. The method of claim 8, further comprising the act of:

providing at least four of the layers.

13. A computer readable medium storing computer code for carrying out the method of claim 1.

14. A programmed computer, programmed to carry out the method of claim 1.