Progressive refinement algorithms for radiant transfer

Issued as Annual progress report, and Final report, Project E-25-M8

PYI (Presidential Young Investigator) award

Issued as Annual progress report, and Final report, Project no. E-25-M7

Radiosity Methods for Volume Rendering

Radiosity methods are techniques for calculating radiative transfer. They were originally introduced in the field of heat transfer, and are descibed in many heat transfer textbooks (e.g. the undergraduate text by Incropera and Dewitt (1990), or the graduate text by Siegel and Howell (1981)). Since calculating global illumination is a radiative transfer problem, radiosity methods have been adapted to image synthesis, beginning with the work of Goral et al. (1984) and Nishita and Nakamae (1985). Over the past seven years many papers describing variations of the radiosity method for rendering surfaces have been published. In these notes, the use of these variations for rendering volumes will be considered. This material can be found in more detail in Rushmeier and Torrance (1997) and Rushmeier (1988)

Extending the Radiosity Method to Include Specularly Reflecting and Translucent Materials

An extension of the radiosity method is presented that rigorously accounts for the presence of a small number of specularly reflecting surfaces in an otherwise diffuse scene, and for the presence of a small number of specular or ideal diffuse transmitters. The relationship between the extended method and earlier radiosity and ray-tracing methods is outlined. It is shown that all three methods are based on the same general equation of radiative transfer. A simple superposition of the earlier radiosity and ray-tracing methods in order to account for specular behavior is shown to be physically inconsistent, as the methods are based on different assumptions. Specular behavior is correctly included in the present method. The extended radiosity method and example images are presented

A New Representation of the Contrast Sensitivity Function for Human Vision

This paper presents a new mathematical representation of the contrast sensitivity function for the human visual system. It is based on optimal smoothing spline fits to vertical and oblique contrast sensitivity measurements. Unlike most of the approximations in current use, which assume isotropy, this new representation incorporates the dependence on orientation revealed by the measurements. One of the uses of the representation is demonstrated by applying it to an example luminance field. Keywords: human vision, contrast sensitivity, luminance fields 1 Introduction The psychophysical response of the human visual system to spatial variations in a perceived luminance field is generally believed to be characterized by a contrast sensitivity function (CSF) which measures the threshold ability to detect such variations as a function of the spatial frequencies in the horizontal and vertical directions. The CSF is measured by observing sinusoidal gratings with varying contrasts and recordin..

Tone Reproduction for Realistic Computer Generated Images

Radiosity and other global illumination methods for image synthesis calculate the 'real world' radiance values of a scene instead of the display radiance values that will represent them. This causes 'display range' problems that are often solved by ad-hoc means, giving little assurance that the evoked visual sensations (brightness, color, etc.) are truly equivalent. Workers in photography have studied such perception matching as 'tone reproduction', and devised correcting operators from both empirical and vision research data. Corrections are usually limited by the chemical/optical restrictions of film. These practical film methods were adopted by television systems and then by computer graphics, despite the ease of implementing better correction operators by computer. In this paper we advocate the use of better tone reproduction for computer graphics. We give a general framework for tone reproduction, where mathematical models of the display device and human observers define an explicit conversion from real-world to display device radiance. These are used to review tone reproduction operators used for film and television. A brief summary of some applicable vision research literature leads to a simple example of an improved operator. We apply the Stevens & Stevens models of brightness vs. luminance relations to our framework to create a new tone reproduction operator for black & white computer generated images. The new operator is shown to be a reasonable solution to the display range problem, and further extensions are suggested