Expressive rendering of mountainous terrain

technical reportPainters and cartographers have developed artistic landscape rendering techniques for centuries. Such renderings can visualize complex three-dimensional landscapes in a pleasing and understandable way. In this work we examine a particular type of artistic depiction, panorama maps, in terms of function and style, and we develop methods to automatically generate panorama map reminiscent renderings from GIS data. In particular, we develop image-based procedural surface textures for mountainous terrain. Our methods use the structural information present in the terrain and are developed with perceptual metrics and artistic considerations in mind

Artistic vision: painterly rendering using computer vision techniques

Journal ArticleWe present a method that takes a raster image as input and produces a painting-like image composed of strokes rather than pixels. Unlike previous automatic painting methods, we attempt to keep the number of brush-stroke small. This is accomplished 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. Our process creates images reminiscent of modern realist painters who often want an abstract or sketchy quality in their work

Automatic painting with economized strokes

Journal ArticleWe present a method that takes a raster image as input and produces a painting-like image composed of strokes rather than pixels. Unlike previous automatic painting methods, we attempt to use very few brush-strokes. This is accomplished 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. Our process creates images reminiscent of modern realist painters who often want an abstract or sketchy quality in their work

Natural image statistics for computer graphics

Journal ArticleThe class of all natural images is an infinitely small fraction of all possible images. The structure of natural images can be statistically modeled, revealing striking regularities. The human visual system appears to be optimized to view natural images, as opposed to any possible image, and therefore expects to interpret images which conform to these statistics. Research has shown that images that do not statistically behave as natural images are harder for the human visual system to interpret. The paper reviews the statistics of natural image and the implications for computer graphics in general are assessed. We argue that these statistics are important for graphics applications and finally, we provide a direct application of these findings to random subdivision terrain modeling

Single sample soft shadows

Journal ArticleA simple extension to ray tracing is presented that creates visually plausible "soft" shadows with little extra computation. Although these soft shadows are approximate, they are robust and have penumbra widths that behave in a believable way, including accurate placement of singularities where penumbra width is zero. The method has continuous behavior in space and time, so it is appropriate for both static and dynamic image generation

Visual glue

technical reportOne key function of graphics systems is to present information about the 3-D structure of modeled environments. For real-time simulations, conveying a sense of contact between touching surfaces and relative position and motion between proximate objects is particularly critical. Neither stereo nor occlusion cues are completely effective for such fine judgments. Conventional wisdom often argues that shadows play a critical role. Less often, it is argued that interreflection also contributes to the sense that two surfaces are touching. This paper explores the actual utility of shadows and interreflection in signaling contact and suggests how this information can be exploited in real-time rendering systems to glue objects to surfaces

Towards interactive global illumination effects via sequential Monte Carlo adaptation

Journal ArticleThis paper presents a novel method that effectively combines both control variates and importance sampling in a sequential Monte Carlo context while handling general single-bounce global illumination effects. The radiance estimates computed during the rendering process are cached in an adaptive per-pixel structure that defines dynamic predicate functions for both variance reduction techniques and guarantees well-behaved PDFs, yielding continually increasing efficiencies thanks to a marginal computational overhead

The use of subtle illumination cues for human judgement of spatial layout

Journal ArticleThe interaction of light with surfaces creates complex lighting effects that provide potentially useful information about the spatial relationships between objects. Previous research has shown cast shadows to be effective in determining the 3D layout of a scene. Interreflections are another are another source of information for spatial relationships; these, however, have been largely ignored in studies of human perception. The purpose of this study was to determine the effectiveness of interreflection for providing cues to contact, and to investigate how interreflection and shadow information combine in the perception of object contact

Parallel point reprojection

Journal ArticleImprovements in hardware have recently made interactive ray tracing practical for some applications. However, when the scene complexity or rendering algorithm cost is high, the frame rate is too low in practice. Researchers have attempted to solve this problem by caching results from ray tracing and using these results in multiple frames via reprojection. However, the reprojection can become too slow when the number of samples that are reused is high, so previous systems have been limited to small images or a sparse set of computed pixels

Temporally coherent interactive ray tracing

Journal ArticleAlthough ray tracing has been successfully applied to interactively render large datasets, supersampling pixels will not be practical in interactive applications for some time. Because large datasets tend to have subpixel detail, one-sample-per-pixel ray tracing can produce visually distracting popping and scintillaction. We present an algorithm that directs primary rays toward locations rendered in previous frames, thereby increasing temporal coherence. Our method tracks intersection points over time, and these tracked points are used as an oracle to aim rays for the next frame. This is in contrast to traditional image-based rendering techniques which advocate color reuse. We so acquire coherence between frames which reduces temporal artifacts without introducing significant processing overhead or causing unnecessary blur