Rendering of photorealistic computer graphics images

#The present invention relates generally to the field of computer imaging. More specifically, techniques and apparatus aimed at fast rendering of photo realistic computer graphic images.

#The ability to synthesize photorealistic images in real-time has been the goal of practitioners in the field of computer graphics for many years. A variety of different techniques are known for generating images of three-dimensional objects on a computer graphics display. One class of techniques divide a two-dimensional array of data values into shaded polygons, which are then projected onto the display screen. To accelerate the image generation process, many polygon-based techniques utilize a special graphics processor to alleviate the computational burden on the computer's central processing unit (CPU).

#Another class of computer imaging techniques is known as ray tracing. Ray tracing is a pixel-based technique that is capable of producing highly realistic images in computer graphic systems. A chief drawback of ray tracing techniques, however, is the extensive computations required to generate each pixel of the display screen. These intensive computations often impose a severe burden on the computer processing hardware. The slow processing times associated with ray tracing techniques have limited their application in computer graphics systems. For example, an article entitled, “Outlook on Computer Graphics”, by D. P. Greenburg, IEEE Computer, 31(1): 36—36 (January 1998), suggests that it will not be until the year 2025 before computer systems have the display and computational capability to produce realistic, real-time images using pixel-based techniques.

#The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings, where:

#FIG. 1 illustrates the rendering pipeline of one embodiment of the present invention.

#FIGS. 2A-2D provide examples illustrating the pixel evaluation process as controlled by the DCM accelerator of the present invention.

#Throughout the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it should be understood that the invention could be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the present invention.

#A new technology for fast rendering of photorealistic computer graphics images is presented. In the context of the present application this new technology is referred to as a directional coherence map (DCM). DCM is a pixel-based, rather than a polygon-based, technology capable of accurately reproducing subtle shading, shadow, and inter-reflection effects that are commonly seen in real-world scenes. As will become apparent to those of ordinary skill in the art, the DCM accelerator significantly speeds up rendering of ray traced displays as compared to conventional techniques. In addition, DCM technology may be implemented in a variety of personal computer graphics hardware.

#The DCM technique for handling general radiance discontinuities in a progressive ray tracing framework includes two primary components: first, an adaptive partitioning of the image plane into blocks, such that each block includes at most one discontinuity edge. Secondly, an estimation of the orientation of the discontinuity edge in each block. The estimation is achieved by computing the “direction of least discrepancy” within the block. The DCM assists in capturing radiance discontinuities by way of finite element approximation to the radiance function, with the finite elements on each block being oriented in accordance with the orientation of the discontinuity within that particular block.