The automatic selection of good viewing parameters is very complex. In most cases, the notion of good strongly depends on the concrete application. Moreover, when an intuitive definition of good view is available, it is often di#cult to establish a measure that brings it to the practice. Commonly, two kind of viewing parameters must be set: the position and orientation of the camera, and the ones relative to light sources. The first ones will determine how much of the geometry can be captured and the latter will influence on how much of it is revealed (i. e. illuminated) to the user. In this paper we will define a metric to calculate the amount of information relative to an object that is communicated to the user given a fixed camera position. This measure is based on an information-based concept, the Shannon entropy, and will be applied to the problem of automatic selection of light positions in order to adequately illuminate an object.

In this paper, we present a lighting design framework for neardiffuse real objects, starting from a set of prerecorded photographs of an object under various lighting conditions. Light sources are placed at fixed positions around an object, for which the intensities are to be determined. Using existing digital imaging software, the lighting designer paints the desired illumination distribution on a photograph of an object. This painted-on illumination is used to determine the light intensities which produce a shading of the real object matching the desired illumination distribution. Certain areas in the painted image can be favored among others by weighting their importance in the optimization algorithm.

An understanding of light and its interaction with matter is essential to produce images. As the modeling of light sources, light transport and light re ection improves, it becomes possible to render images with increasing realism. The central motivation behind this thesis is to improve realism in computer graphics images by more accurate local shading models and to assist the user to obtain the desired lighting e ects with these more complex models. The rst part of the thesis addresses the problem of rendering surfaces illuminated by extended (linear and area) light sources. To compute the light re ected by a surface element ina given direction, one needs to determine the unoccluded regions (shadowing) of each light source and then to compute the light re ection (shading) from each of these regions. Traditionally, point light sources are distributed on the lights to approximate both the shadowing and the shading. Instead, an e cient analytical solution is developed for the shading. Shadowing from extended light sources is a fairly expensive process. To give some insights on the complexity of computing shadows, some properties of shadows and algorithms are presented. To reduce the cost of computing shadows from linear light sources, two acceleration schemes, extended from

Figure 1: An example output. (a) the original hip model with 40,000 triangles. (b) The user uses orange and blue strokes to bring the cavity into focus and recede the rear part by darkening it. (c) a sample output produced by our system by moving the existing light and adding a new light. This image is rendered using conventional OpenGL rendering. (d) compliance with the input is reinforced by this raytraced image of the same model under the same lighting conditions, with shadowing effects. An interactive and intuitive way of designing lighting around a model is desirable in many applications. In this paper, we present a tool for interactive inverse lighting in which a model is rendered based on sketched lighting effects. To specify target lighting, the user freely sketches bright and dark regions on the model as if coloring it with crayons. Using these hints and the geometry of the model, the system efficiently derives light positions, directions, intensities and spot angles, assuming a local point-light based illumination model. As the system also minimizes changes from the previous specifications, lighting can be designed incrementally. We formulate the inverse lighting problem as that of an optimization and solve it using a judicious mix of greedy and minimization methods. We also map expensive calculations of the optimization to graphics hardware to make the process fast and interactive. Our tool can be used to augment larger systems that use point-light based illumination models but lack intuitive interfaces for lighting design, and also in conjunction with applications like ray tracing where interactive lighting design is difficult to achieve.

This thesis presents a method for creating simulated oil paintings. A raster image is next used as input to an algorithm that produces a painting-like image composed of brush strokes rather than pixels. Ultimately the sequence of brush strokes representing an interpreted image can be rendered in pixel form, however the brush stroke structure is far more compact for storage and transmission. Unlike previous automatic painting methods, this algorithm attempts to use very few brush-strokes. The algorithm achieves economy of brush strokes by first segmenting the image into features, finding the medial axes points of these features, converting the medial axes points into ordered lists of image tokens, and finally rendering these lists as brush strokes. The process creates images reminiscent of modern realist painters who often want an abstract or sketchy quality in their work. To Amy, More than the Sun, the Moon, and all the Stars. CONTENTS ABSTRACT........................................................ ACKNOWLEDGEMENTS............................................ ii

Current trends in 3D graphics point to a near future when our ability to gener-ate 3D content will far surpass our ability to analyze it meaningfully. These trends have inspired us to improve the comprehensibility of 3D graphics rendering using in-sights from human perception of geometry and illumination. In this dissertation, we develop algorithms and systems to seamlessly integrate the low-level human visual system cues with object modeling and lighting for 3D graphics. Artists and illustrators have enhanced the perception of shape with discrepant lighting for centuries. Traditional graphics however assumes a model of consistent lighting. We have developed a lighting design system, that by relaxing the constraint of consistent lighting is able to convey a better depiction of shape. Our system for automatic lighting design, Light Collages, segments the objects into local surface patches and uses careful placement of highlights, shadows, and silhouettes on them to enhance shape perception. We have developed a spherical-harmonics-based for-mulation to achieve a 20-fold improvement in speed. Geometric processing in graphics has made significant advances over the last

Thanks to an increase in rendering efficiency, indirect illumination has recently begun to be integrated in cinematic lighting design, an application where physical accuracy is less important than careful control of scene appearance. This paper presents a comprehensive, efficient, and intuitive representation for artistic control of indirect illumination. We encode user’s adjustments to indirect lighting as scale and offset coefficients of the transfer operator. We take advantage of the nature of indirect illumination and of the edits themselves to efficiently sample and compress them. A major benefit of this sampled representation, compared to encoding adjustments as procedural shaders, is the renderer-independence. This allowed us to easily implement several tools to produce our final images: an interactive relighting engine to view adjustments, a painting interface to define them, and a final renderer to render high quality results. We demonstrate edits to scenes with diffuse and glossy surfaces and animation. Categories and Subject Descriptors (according to ACM CCS):

In this paper, we present a lighting design framework for glossy real objects, starting from the reflectance field of an object. Using existing digital imaging software, the lighting designer paints the desired illumination distribution on a photograph of an object. This painted-on illumination is used to determine the light intensities which produce a shading of the real object matching the desired illumination distribution. Certain areas in the painted image can be favored among others by weighting their importance in the optimization algorithm. Our optimization algorithm is driven by a simulated annealing approach to find fixed-sized lighting combinations and accompagnying intensities.

Abstract — Physically based rendering of metallic and pearlescent appearance requires knowledge of the composition of paint or coating. However, sometimes composition is not available, while the Bi-directional Reflectance Distribution Function (BRDF) is measured from an actual sample. Such a situation invokes the inverse problem- to find a paint composition from a given BRDF. We solve this problem based on a two-layer paint model, where two basic kinds of pigments, flakes and microparticles, are separated in different layers. Because of this, appearance attributes- such as gloss, glitter, shade- are directly connected to the physical parameters of our model. Therefore, solution of the inverse problem can serve as a starting point for subsequent paint design that is done in appearancerelated rather than physical terms. Our solution involves two consecutive optimizations, which are calculated in real time on a contemporary PC. I.

This thesis demonstrates the way in which various methods for controlling detail and creating effects in computer graphics may be unified under the general theme of the rendering filter. Generally stated, such a filter is a passive, stateless operator that acts upon a decomposition of terms in the rendering equation. In the first Part, we present background that motivates this concept, and provides an understanding of the way in which the rendering filter follows logically from existing use in other domains. First, in Chapter 1, we discuss the general and historical use of the term “filter, ” especially as a useful metaphor that encapsulates various similar operations. We present examples of filters in photography, electronics, imaging and geometry processing. In Chapter 2, we provide background specific to rendering in graphics, examine the process of rendering as inherently related to filtering, and define the rendering filter itself. In the second Part, we see the application of these concepts by three specific examples of rendering filters. In addition to demonstrating the utility of the methods themselves, we show how these distinct algorithms are unified by the underlying rendering filter framework. In Chapter 3, we show various ways in which artists use “abstract, ” or