GTX. The scene is illuminated with a small spot light (upper right); all other illumination and shadowing is indirect (one bounce). We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps—low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

High-fidelity rendering of complex scenes at interactive rates is one of the primary goals of computer graphics. Since high-fidelity rendering is computationally expensive, perceptual strategies such as visual attention have been explored to achieve this goal. In this paper we investigate how two models of human visual attention can be exploited in a selective rendering system. We examine their effects both individually, and in combination, through psychophysical experiments to measure savings in computation time while preserving the perceived visual quality for a task-related scene. We adapt the lighting simulation system Radiance to support selective rendering, by introducing a selective guidance system which can exploit attentional processes using an importance map. Our experiments demonstrate that viewers performing a visual task within the environment consistently fail to notice the difference between high quality and selectively rendered images, computed in a significantly reduced time.

Optical systems used in photography and cinema produce depth of field effects, that is, variations of focus with depth. These effects are simulated in image synthesis by integrating incoming radiance at each pixel over the lense aperture. Unfortunately, aperture integration is extremely costly for defocused areas where the incoming radiance has high variance, since many samples are then required for a noise-free Monte Carlo integration. On the other hand, using many aperture samples is wasteful in focused areas where the integrand varies little. Similarly, image sampling in defocused areas should be adapted to the very smooth appearance variations due to blurring. This paper introduces an analysis of focusing and depth of field in the frequency domain, allowing a practical characterization of a light field’s frequency content both for image and aperture sampling. Based on this analysis we propose an adaptive depth of field rendering algorithm which optimizes sampling in two important ways. First, image sampling is based on conservative bandwidth prediction and a splatting reconstruction technique ensures correct image reconstruction. Second, at each pixel the variance in the radiance over the aperture is estimated, and used to govern sampling. This technique is easily integrated in any sampling-based renderer, and vastly improves performance.

Figure 1: Examples of inequivalent and equivalent VPL rendering. (a)-(b) are VPL renderings with 1k VPLs, and clamp levels C1 = 316 and C8 = 0.1, respectively, that are not equivalent (̸≡) to the reference (d) because they have image artifacts (a) or different perceived material appearance (b). (c) VPL rendering produces an image that is visually equivalent (≡) to the reference for 100k VPLs and clamp level C4 = 10, even though some reflections are lost where the Dragon is in contact with the pedestal and around its silhouette. Rendering applications in design, manufacturing, ecommerce and other fields are used to simulate the appearance of objects and scenes. Fidelity with respect to appearance is often critical, and calculating global illumination (GI) is an important contributor to image fidelity; but it is expensive to compute. GI approximation methods, such as virtual point light (VPL) algorithms, are efficient, but they can induce image artifacts and distortions of object appearance. In this paper we systematically study the perceptual effects on image quality and material appearance of global illumination approximations made by VPL algorithms. In a series of psychophysical experiments we investigate the relationships between rendering parameters, object properties and image fidelity in a VPL renderer. Using the results of these experiments we analyze how VPL counts and energy clamping levels affect the visibility of image artifacts and distortions of material appearance, and show how object geometry and material properties modulate these effects. We find the ranges of these parameters that produce VPL renderings that are visually equivalent to reference renderings. Further we identify classes of shapes and materials that cannot be accurately rendered using VPL methods with limited resources. Using these findings we propose simple heuristics to guide visually equivalent and efficient rendering, and present a method for correcting energy losses in VPL renderings. This work provides a strong perceptual foundation for a popular and efficient class of GI algorithms.

The computational requirements of full global illumination rendering are such that it is still not possible to achieve high-fidelity graphics of very complex scenes in a reasonable time on a single computer. By identifying which computations are more relevant to the desired quality of the solution, selective rendering can significantly reduce rendering times. In this paper we present a novel component-based selective rendering system in which the quality of every image, and indeed every pixel, can be controlled by means of a component regular expression (crex). The crex provides a flexible mechanism for controlling which components are rendered and in which order. It can be used as a strategy for directing the light transport within a scene and also in a progressive rendering framework. Furthermore, the crex can be combined with visual perception techniques to reduce rendering computation times without compromising the perceived visual quality. By means of a psychophysical experiment we demonstrate how the crex can be successfully used in such a perceptual rendering framework. In addition, we show how the crex’s flexibility enables it to be incorporated in a predictive framework for time-constrained rendering.

Efficient and visually compelling reproduction of effects due to multiple scattering in participating media remains one of the most difficult tasks in computer graphics. Although several fast techniques were recently developed, most of them work only for special types of media (for example, uniform or sufficiently dense) or require extensive precomputation. In this paper we present a lighting model for the general case of inhomogeneous medium and demonstrate its implementation on programmable graphics hardware. It is capable of producing high quality imagery at interactive frame rates with only mild assumptions about medium scattering properties and a moderate amount of simple precomputation.

Realistic image synthesis is the process of computing photorealistic images which are perceptually and measurably indistinguishable from real-world images. In order to obtain high fidelity rendered images it is required that the physical processes of materials and the behavior of light are accurately modelled and simulated. Most computer graphics algorithms assume that light passes freely between surfaces within an environment. However, in many applications, ranging from evaluation of exit signs in smoke filled rooms to design of efficient headlamps for foggy driving, realistic modelling of light propagation and scattering is required. The computational requirements for calculating the interaction of light with such participating media are substantial. This process can take many minutes or even hours. Many times rendering efforts are spent on computing parts of the scene that will not be perceived by the viewer. In this paper we present a novel perceptual strategy for physicallybased rendering of participating media. By using a combination of a saliency map with our new extinction map (X-map) we can significantly reduce rendering times for inhomogenous media. We also validate the visual quality of the resulting images using two objective difference metrics and a subjective psychophysical experiment. Although the average pixel errors of these metric are all less than 1%, the experiment using human observers indicate that these degradation in quality is still noticeable in certain scenes, unlike previous work has suggested.

Texture fractalization is used in many existing approaches to ensure the temporal coherence of a stylized animation. This paper presents the results of a psychophysical user-study evaluating the relative distortion induced by a fractalization process of typical medium textures. We perform a ranking experiment, assess the agreement among the participants and study the criteria they used. Finally we show that the average co-occurrence error is an efficient quality predictor in this context.

Much research in recent times has been conducted towards realtime rendering of accurate glossy reflections under direct, natural illumination including correct occlusions. The view dependent nature of these reflections will always cause this computation to be expensive unless heavily approximated. There also remains a question as to whether humans are even capable of noticing the difference in accuracy or whether our perception of the realism of the scene remains unchanged and thus the extra effort expended in rendering accurate reflections is effectively wasted. We conduct a user study to analyse any decline in perceived realism of glossy scenes rendered with a variety of specular occlusion approximations under a multitude of BRDFs, lighting environments and camera orientations. We demonstrate that although no one approximation is always suitable, it is rare to have a scene whose computational complexity cannot be decreased to some degree.

High-fidelity renderings of virtual environments is a notoriously computationally expensive task. One commonly used method to alleviate the costs is to adaptively sample the rendered images identifying the required number of samples according to the variance of the area thus reducing aliasing and concurrently reducing the total number of rays shot. When using ray tracing algorithms, the traditional method is to shoot a number of rays and depending on the difference between the radiance of the samples further rays may be shot. This approach fails to take into account that different components of a material reflecting light may exhibit more coherence than others. With this in mind we present a component-based adaptive sampling algorithm that renders components individually and adaptively samples at the component level, finally composting the result to produce a full solution. Results demonstrate a significant improvement in performance without any perceptual loss in quality.