Image rendering maps scene parameters to output pixel values; animation maps motion-control parameters to trajectory values. Because these mapping functions are usually multidimensional, nonlinear, and discontinuous, #nding input parameters that yield desirable output values is often a painful process of manual tweaking. Interactiveevolution and inverse design are two general methodologies for computer-assisted parameter setting in which the computer plays a prominent role. In this paper we present another such methodology.

It is often difficult in computer graphics applications to understand spatial relationships between objects in a 3D scene or effect changes to those objects without specialized visualization and manipulation techniques. We present a set of three-dimensional tools (widgets) called "shadows" that not only provide valuable perceptual cues about the spatial relationships between objects, but also provide a direct manipulation interface to constrained transformation techniques. These shadow widgets provide two advancesover previous techniques. First, they provide high correlation between their own geometric feedback and their effects on the objects they control. Second, unlike some other 3D widgets, they do not obscure the objects they control. Keywords Direct Manipulation, 3D Widgets, Interactive Systems 1 Introduction A wide variety of techniques for visualizing and manipulating objects have beenimplemented in interactive 3D graphics applications for modeling, animation, simulation an...

This paper draws from art history and perception to place computer depiction in the broader context of picture production. It highlights the often underestimated complexity of the interactions between features in the picture and features of the represented scene. Depiction is not always a unidirectional projection from a 3D scene to a 2D picture, but involves much feedback and influence from the picture space to the object space. Depiction can be seen as a pre-existing 3D reality projected onto 2D, but also as a 2D pictorial representation that is superficially compatible with an hypothetic 3D scene. We show that depiction is essentially an optimization problem, producing the best picture given goals and constraints. We introduce a classification of basic depiction techniques based on four kinds of issue. The spatial system deals with the mapping of spatial properties between 3D and 2D (including, but not restricted to, perspective projection). The primitive system deals with the dimensionality and mappings between picture primitives and scene primitives. Attributes deal with the assignment of visual properties such as colors, texture, or thickness. Finally, marks are the physical implementations of the picture (e.g. brush strokes, mosaic cells). A distinction is introduced between interaction and picturegeneration methods, and techniques are then organized depending on the dimensionality of the inputs and outputs.

This paper presents a method for designing the illumination in an environment using optimization techniques applied to a radiosity based image synthesis system. An optimization of lighting parameters is performed based on user specified constraints and objectives for the illumination of the environment. The system solves for the "best" possible settings for: light source emissivities, element reflectivities, and spot light directionality parameters so that the design goals, suchastominimize energy or to give the the room an impression of privacy, are met. The system absorbs much of the burden for searching the design space allowing the user to focus on the goals of the illumination design rather than the intricate details of a complete lighting specification. A software implementation is described and some results of using the system are reported.

Placing shadows is difficult task since shadows depend on the relative positions of lights and objects in an unintuitive manner. To simplify the task of the modeler, we present a user interface for designing shadows in 3d environments. In our interface, shadows are treated as first-class modeling primitives just like objects and lights. To transform a shadow, the user can simply move, rescale or rotate the shadow as if it was a 2d object on the scene’s surfaces. When the user transforms a shadow, the system moves lights or objects in the scene as required and updates the shadows in realtime during mouse movement. To facilitate interaction, the user can also specify constraints that the shadows must obey, such as never casting a shadow on the face of a character. These constraints are then verified in real-time, limiting mouse movement when necessary. We also integrate in our interface fake shadows typically used in computer animation. This allows the user to draw shadowed and non-shadowed regions directly on surfaces in the scene.

Lighting has a crucial impact on the appearance of 3D objects and on the ability of an image to communicate information about a 3D scene to a human observer. This paper presents a new automatic lighting design approach for comprehensible rendering of 3D objects. Given a geometric model of a 3D object or scene, the material properties of the surfaces in the model, and the desired viewing parameters, our approach automatically determines the values of various lighting parameters by optimizing a perception-based image quality objective function. This objective function is designed to quantify the extent to which an image of a 3D scene succeeds in communicating scene information, such as the 3D shapes of the objects, fine geometric details, and the spatial relationships between the objects.

this paper we will describe and illustrate work in our laboratory where the emphasis is on extracting illumination information from real images and computing the common illumination between the real and the computer generated scene. 1. Introduction

direct indirect paint-all paint-one lighting lighting lighting painting lighting painting 225- s: key refinement 215- s: key refinement 240- s: lighting features 285- s: adjustments 160-225 s: fill light 190-215 s: fill light 135-240 s: intensity 140-265 s: key intensity 75-160 s: key light 155-175 s: key light 0-70 s: background 65-140 s: key hotspot Figure 1: Example workflow of a novice subject lighting a simple scene with one key and one fill light using four different lighting interfaces.

shaped halls bring the audience closer to the stag e than other configBCSq;BCD but they may fail to make the listener feel surrounded by the sound. The application ofhig( y absorbent materials may reducedisturbing echoes, but they may also deaden the hall. In many renovations,budg etary, aesthetic, or physical impediments limit modifications, compounding the difficultiesconfronting thedesig(3 . In addition, a hall migq need to accommodate a widerang e of performances, from lectures to symphonic music, each with different acoustic requirements. In short, a concert hall's acoustics depends on thedesigCS 's ability to balance many factors. Here, we present an inverse, interactive acoustic desig approach that helps adesig(q produce an architecturalconfigqC: CVD that achieves a desired acoustic performance. For a newbuilding the system maysug g est optimalconfig3BB:q;0 that would not otherwise be considered; for a hall with modifiable components or for a renovation project, it may assist in

Figure 1: Traditional computer graphics algorithms produce “accurate ” shadows (left). Artists often deliberately render abstract shadows, such as the shadow with reduced contour detail in this painting by Vanderlyn, 1818 (middle). Our system offers controls for creation of stylized shadows (right). While much research has focused on rendering physically-correct shadows, a “correct ” shadow often exhibits unnecessary detail that distracts from the primary subject of the scene. Artists often prefer to have creative control over the rendered appearance of the shadow. This paper presents an algorithm offering control over stylized shadows, based on four intuitive parameters – inflation, brightness, softness, and abstraction – that together support a broad range of effects. The algorithm, which works largely in image space, can easily be incorporated into existing rendering pipelines, and is independent of scene geometry or shadow determination method. 1