Issue 2

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/61

Browse

Browsing Issue 2 by Title

Now showing 1 - 6 of 6
  • No Thumbnail Available
    Item
    Constant-Time Filtering by Singular Value Decomposition?
    (Blackwell Science Ltd and the Eurographics Association, 1994) Gotsman, Craig
    We present a technique implementing space-variant filtering of an image, with kernels belonging to a given family, in time independent of the size and shape of the filter kernel support. The essence of our method is efficient approximation of these kernels, belonging to an infinite family governed by a small number of parameters, as a linear combination of a small number k of"basis" kernels. The accuracy of this approximation increases with k, and requires O(k) storage space. Any kernel in the family may be applied to the image in O(k) time using precomputed results of the application of the basis kernels. Performing linear combinations of these values with appropriate coefficients yields the desired result. A trade off between algorithm efficiency and approximation quality is obtained by adjusting k.The basis kernels are computed using singular value decomposition, distinguishing this from previous techniques designed to achieve a similar effect. We illustrate by applying our methods to the family of elliptic Gaussian kernels, a popular choice for filtering warped images.
  • No Thumbnail Available
    Item
    Five-dimensional Adaptive Subdivision for Ray Tracing
    (Blackwell Science Ltd and the Eurographics Association, 1994) Simiakakis, G.; Day, A. M.
    This paper presents a directional subdivision method for speeding up ray tracing. This method is easy to use, because it automatically adapts the subdivision to the scene relieving the user from having to set parameters for the subdivision. It also attempts a balance between 5D and spatial subdivision in order to benefit from both methods. A memory saving scheme is introduced and experimental results are presented.
  • No Thumbnail Available
    Item
    Making Shaders More Physically Plausible
    (Blackwell Science Ltd and the Eurographics Association, 1994) Lewis, Robert R.
    There is a need to develop shaders that not only"look good", but are more physically plausible. From physical and geometric considerations, we review the derivation of a shading equation expressing rejected radiance in terms of incident radiance and the bidirectional reflectance distribution function (BRDF). We then examine the connection between this equation and conventional shaders used in computer graphics. Imposing the additional physical constraints of energy conservation and Helmholtz reciprocity allows us to create variations of the conventional shaders that are more physically plausible.
  • No Thumbnail Available
    Item
    A Survey of Shading and Reflectance Models
    (Blackwell Science Ltd and the Eurographics Association, 1994) Schlick, Christophe
    Since the beginning of computer graphics, three decades ago, a large number of models intended to describe the behaviour of light on a given point of a surface have been proposed. Almost every author uses his own terminology and/or notation. To understand clearly the similarities and the differences between existing models, reformulating them with a unified notation is essential. This has been done by Hall in 1986. This paper is a new survey of shading and reflectance models, including the most recent models. Moreover, after the lengthy enumeration, some original models are proposed, which attempt to include interesting features of previous disjointed work into new formulations.
  • No Thumbnail Available
    Item
    A Theoretical Framework for Physically Based Rendering
    (Blackwell Science Ltd and the Eurographics Association, 1994) Lafortune, Eric P.; Willems, Yves D.
    In this paper we introduce the concept of the global reflection distribution function which allows concise formulation of the global illumination problem. Unlike previous formulations it is not geared towards any specific algorithm. As an example of its versatility we derive a Monte Carlo rendering algorithm that seamlessly integrates the ideas of shooting and gathering power to create photorealistic images.
  • No Thumbnail Available
    Item
    Wavelet Projections for Radiosity
    (Blackwell Science Ltd and the Eurographics Association, 1994) Schröder, Peter; Gortler, Steven J.; Cohen, Michael F.; Hanrahan, Pat
    One important goal of image synthesis research is to accelerate the process of obtaining realistic images using the radiosity method. Two important concepts recently introduced are the general framework of projection methods and the hierarchical radiosity method.Wavelet theory, which explores the space of hierarchical basis functions, offers an elegant framework that unites these two concepts and allows us to more formally understand the hierarchical radiosity method.Wavelet expansions of the radiosity kernel have negligible entries in regions where high frequency/fine detail information is not needed. A sparse system remains if these entries are ignored. This is similar to applying a lossy compression scheme to the form factor matrix. The sparseness of the system allows for asymptotically faster radiosity algorithms by limiting the number of matrix terms that need to be computed. The application of these methods to 3D environments is described in4. Due to space limitations in that paper many of the subtleties of the construction could not be explored there. In this paper we discuss some of the mathematical details of wavelet projections and investigate the application of these methods to the radiosity kernel of a flatland environment, where many aspect are easier to visualize.