Refraction in Discrete Ray Tracing

Refraction is an important graphics feature for synthesizing photorealistic images. This paper presents a study on refraction rendering in volume graphics using discrete ray tracing. We describe four basic approaches for determining the relative refractive index at each sampling position, and examine their relative merits. We discuss two types of anomalies associated with some approaches and three different mechanisms for controlling sampling intervals. We apply the refraction rendering to objects with uniform as well as non-uniform optical density, and objects built upon mathematical scalar fields as well as volumetric datasets. In particular, the study shows that the normal estimation plays a critical role in synthesizing aesthetically pleasing images. The paper also includes the results of various tests, and our quantitative and qualitative analysis.