Abstract Reconstructing outdoor environments from “inside-out” captures, where a camera moves within a restricted area but looks outward, remains challenging due to the presence of both well-textured nearby regions and low-detail distant backgrounds. We introduce a two-stage Gaussian Splatting framework that explicitly separates and optimizes these regions, yielding higher-fidelity novel view synthesis and allowing the replacement of the distant part with a high-quality, inpainted environment map to speedup the rendering process. In stage one, background primitives are initialized within a spherical shell and optimized using a loss that combines a background-only photometric term with two geometric regularizers: one constraining Gaussians to remain inside the shell, and another one aligning them with local tangential planes. In stage two, foreground Gaussians are initialized from a Structure-from-Motion reconstruction, added and refined using the standard rendering loss, while the background set remains fixed but contributes to the final image formation. Background Gaussians can be rendered to an object-free environment map that is inpainted to fill missing parts and can replace the Gaussian-based background for faster rendering. Experiments on diverse outdoor datasets show that our method reduces background artifacts and improves perceptual quality of novel view renderings compared to state-of-the-art baselines, including the removal of floaters in the navigation region.

Procedural implicit surfaces are a popular representation for shape modeling. They provide a simple framework for complex geometric operations such as Booleans, blending and deformations. However, their editability remains a challenging task: as the definition of the shape is purely implicit, direct manipulation of the shape cannot be performed. Thus, parameters of the model are often exposed through abstract sliders, which have to be nontrivially created by the user and understood by others for each individual model to modify. Further, each of these sliders needs to be set one by one to achieve the desired appearance. To circumvent this laborious process while preserving editability, we propose to directly manipulate the implicit surface in the viewport. We let the user naturally interact with the output shape, leveraging points on a co-parameterization we design specifically for implicit surfaces, to guide the parameter updates and reach the desired appearance faster. We leverage our automatic differentiation of the procedural implicit surface to propagate interactions made by the user in the viewport to the shape parameters themselves. We further design a solver that uses such information to guide an intuitive and smooth user workflow. We demonstrate different editing processes across multiple implicit shapes and parameters that would be tedious by tuning sliders.

The use of version control is pervasive in collaborative software projects. Version control systems are based on two primary operations: diffing two versions to compute the change between them and merging two versions edited concurrently. Recent works provide solutions to diff and merge graphics assets such as images, meshes and scenes. In this work, we present a practical algorithm to diff and merge procedural programs written as node graphs. To obtain more precise diffs, we version the graphs directly rather than their textual representations. Diffing graphs is equivalent to computing the graph edit distance, which is known to be computationally infeasible. Following prior work, we propose an approximate algorithm tailored to our problem domain. We validate the proposed algorithm by applying it both to manual edits and to a large set of randomized modifications of procedural shapes and materials. We compared our method with existing state-of-the-art algorithms, showing that our approach is the only one that reliably detects user edits.

We present a practical framework to port Bézier curves to surfaces. We support the interactive drawing and editing of Bézier splines on manifold meshes with millions of triangles, by relying on just repeated manifold averages. We show that direct extensions of the de Casteljau and Bernstein evaluation algorithms to the manifold setting are fragile, and prone to discontinuities when control polygons become large. Conversely, approaches based on subdivision are robust and can be implemented efficiently. We implement manifold extensions of the recursive de Casteljau bisection, and an open-uniform Lane-Riesenfeld subdivision scheme. For both schemes, we present algorithms for curve tracing, point evaluation, and approximated point insertion. We run bulk experiments to test our algorithms for robustness and performance, and we compare them with other methods at the state of the art, always achieving correct results and superior performance. For interactive editing, we port all the basic user interface interactions found in 2D tools directly to the mesh. We also support mapping complex SVG drawings to the mesh and their interactive editing.

Abstract Procedural materials are extensively used in computer graphics, since they provide editable, resolution‐independent representation of textures. However, tuning the parameters of procedural generators to achieve a desired result remains time‐consuming for users. Recently, inverse procedural material algorithms have been developed, exploiting differentiable rendering methods to find the parameters of a procedural model that match a target image. These approaches focus on raster textures. We propose pOp, a practical method for estimating the parameters of vector patterns, that are formed by collections of vector shapes arranged by an arbitrary procedural program. In our approach, patterns are defined as arbitrary programs, that control the translation, rotation and scale or vector graphics elements. We support elements typical of vector graphics, namely points, lines, circle, rounded rectangles, and quadratic Bèzier drawings, in multiple colors. We optimize the program parameters by automatically differentiating the signed distance field of the drawing, which we found to be significantly more reliable than using differentiable rendering of the final image. We demonstrate our method on a variety of cases, representing the variations found in structured vector patterns.

Boolean operations are among the most used paradigms to create and edit digital shapes. Despite being conceptually simple, the computation of mesh Booleans is notoriously challenging. Main issues come from numerical approximations that make the detection and processing of intersection points inconsistent and unreliable, exposing implementations based on floating point arithmetic to many kinds of degeneracy and failure. Numerical methods based on rational numbers or exact geometric predicates have the needed robustness guarantees, that are achieved at the cost of increased computation times that, as of today, has always restricted the use of robust mesh Booleans to offline applications. We introduce an algorithm for Boolean operations with robustness guarantees that is capable of operating at interactive frame rates on meshes with up to 200K triangles. We evaluate our tool thoroughly, considering not only interactive applications but also batch processing of large collections of meshes, processing of huge meshes containing millions of elements and variadic Booleans of hundreds of shapes altogether. In all these experiments, we consistently outperform prior robust floating point methods by at least one order of magnitude.

Many real-world hand-crafted objects are decorated with elements that are packed onto the object’s surface and deformed to cover it as much as possible. Examples are artisanal ceramics and metal jewelry. Inspired by these objects, we present a method to enrich surfaces with packed volumetric decorations. Our algorithm works by first determining the locations in which to add the decorative elements and then removing the non-physical overlap between them while preserving the decoration volume. For the placement, we support several strategies depending on the desired overall motif. To remove the overlap, we use an approach based on implicit deformable models creating the qualitative effect of plastic warping while avoiding expensive and hard-to-control physical simulations. Our decorative elements can be used to enhance virtual surfaces, as well as 3D-printed pieces, by assembling the decorations onto real surfaces to obtain tangible reproductions.

Tangles are complex patterns, which are often used to decorate the surface of real-world artisanal objects. They consist of arrangements of simple shapes organized into nested hierarchies, obtained by recursively splitting regions to add progressively finer details. In this article, we show that 3D digital shapes can be decorated with tangles by working interactively in the intrinsic metric of the surface. Our tangles are generated by the recursive application of only four operators, which are derived from tracing the isolines or the integral curves of geodesics fields generated from selected seeds on the surface. Based on this formulation, we present an interactive application that lets designers model complex recursive patterns directly on the object surface without relying on parametrization. We reach interactive speed on meshes of a few million triangles by relying on an efficient approximate graph-based geodesic solver.

We port Boolean set operations between 2D shapes to surfaces of any genus, with any number of open boundaries. We combine shapes bounded by sets of freely intersecting loops, consisting of geodesic lines and cubic Bézier splines lying on a surface. We compute the arrangement of shapes directly on the surface and assign integer labels to the cells of such arrangement. Differently from the Euclidean case, some arrangements on a manifold may be inconsistent. We detect inconsistent arrangements and help the user to resolve them. Also, we extend to the manifold setting recent work on Boundary-Sampled Halfspaces, thus supporting operations more general than standard Booleans, which are well defined on inconsistent arrangements, too. Our implementation discretizes the input shapes into polylines at an arbitrary resolution, independent of the level of resolution of the underlying mesh. We resolve the arrangement inside each triangle of the mesh independently and combine the results to reconstruct both the boundaries and the interior of each cell in the arrangement. We reconstruct the control points of curves bounding cells, in order to free the result from discretization and provide an output in vector format. We support interactive usage, editing shapes consisting up to 100k line segments on meshes of up to 1M triangles.

One of the most challenging aspects of the implementation of Virtual/Mixed reality training systems is the effective simulation of real-world manipulation of the physical devices included in control interfaces like buttons, sliders, levers, knobs, etc. In this paper we describe a mockup airplane cockpit (XR-Cockpit), featuring interactive components of this kind that demonstrate the feasibility of effective simulations of device manipulation using low cost hand tracking technology and gesture recognition. Based on this system, we performed a user study to compare the effectiveness of the interaction with virtual tools using different visualization solutions: immersive VR, optical and video see-through based MR. In our study, we also checked how well it is possible to perform manipulation of real objects wearing the two video see-through solutions. The analysis of the experimental results provides useful guidelines for the design of Virtual and Mixed Reality training systems involving virtual and physical actions on manipulation devices.

Abstract Reflectance transformation imaging (RTI) is a computational photography technique widely used in the cultural heritage and material science domains to characterize relieved surfaces. It basically consists of capturing multiple images from a fixed viewpoint with varying lights. Handling the potentially huge amount of information stored in an RTI acquisition that consists typically of 50–100 RGB values per pixel, allowing data exchange, interactive visualization, and material analysis, is not easy. The solution used in practical applications consists of creating “relightable images” by approximating the pixel information with a function of the light direction, encoded with a small number of parameters. This encoding allows the estimation of images relighted from novel, arbitrary lights, with a quality that, however, is not always satisfactory. In this paper, we present NeuralRTI, a framework for pixel-based encoding and relighting of RTI data. Using a simple autoencoder architecture, we show that it is possible to obtain a highly compressed representation that better preserves the original information and provides increased quality of virtual images relighted from novel directions, especially in the case of challenging glossy materials. We also address the problem of validating the relight quality on different surfaces, proposing a specific benchmark, SynthRTI, including image collections synthetically created with physical-based rendering and featuring objects with different materials and geometric complexity. On this dataset and as well on a collection of real acquisitions performed on heterogeneous surfaces, we demonstrate the advantages of the proposed relightable image encoding.

Version control systems are the foundation of collaborative workflows for text documents. For 3D environments though, version control is still an open problem due to the heterogeneous data of 3D scenes and their size. In this paper, we present a practical version control system for 3D scenes comprised of shapes, materials, textures, and animations, combined together in scene graphs. We version objects at their finest granularity, to make repositories smaller and to allow artists to work concurrently on the same object. Since, for some scene data, computing an optimal set of changes between versions is not computationally feasible, version control systems use heuristics. Compared to prior work, we propose heuristics that are efficient, robust, and independent of the application. We test our system on a variety of large scenes edited with different workflows, and show that our approach can handle all cases well while remaining efficient as scene size increases. Compared to prior work, we are significantly faster and more robust. A user study confirms that our system aids collaboration.

Abstract Mimicking the appearance of the real world is a longstanding goal of computer graphics, with several important applications in the feature film, architecture and medical industries. Images with well‐designed shading are an important tool for conveying information about the world, be it the shape and function of a computer‐aided design (CAD) model, or the mood of a movie sequence. However, authoring this content is often a tedious task, even if undertaken by groups of highly trained and experienced artists. Unsurprisingly, numerous methods to facilitate and accelerate this appearance editing task have been proposed, enabling the editing of scene objects' appearances, lighting and materials, as well as entailing the introduction of new interaction paradigms and specialized preview rendering techniques. In this review, we provide a comprehensive survey of artistic appearance, lighting and material editing approaches. We organize this complex and active research area in a structure tailored to academic researchers, graduate students and industry professionals alike. In addition to editing approaches, we discuss how user interaction paradigms and rendering back ends combine to form usable systems for appearance editing. We conclude with a discussion of open problems and challenges to motivate and guide future research.

Collaborative systems are well established solutions for sharing work among people. In computer graphics these workflows are still not well established, compared to what is done for text writing or software development. Usually artists work alone and share their final models by sending files. In this paper we present a system for collaborative 3D digital sculpting. In our prototype, multiple artists concurrently sculpt a polygonal mesh on their local machines by changing its vertex properties, such as positions and material BRDFs. Our system shares the artists' edits automatically and seamlessly merges these edits even when they happen on the same region of the surface. We propose a merge algorithm that is fast-enough for seamless collaboration, respects users' edits as much as possible, can support any sculpting operation, and works for both geometry and appearance modifications. Since in sculpting artists alternatively perform fine adjustments and large scale modifications, our algorithm is based on a multiresolution edit representation that handles concurrent overlapping edits at different scales. We tested our algorithm by modeling meshes collaboratively in different sculpting sessions and found that our algorithm outperforms prior works on collaborative mesh editing in all cases.

The solution of large sparse systems of linear constraints is at the base of most interactive solvers for physically-based animation of soft body dynamics. We focus on applications with hard and tight per-frame resource budgets, such as video games, where the solution of soft body dynamics needs to be computed in a few milliseconds. Linear iterative methods are preferred in these cases since they provide approximate solutions within a given error tolerance and in a short amount of time. We present a parallel randomized Gauss-Seidel method which can be effectively employed to enable the animation of 3D soft objects discretized as large and irregular triangular or tetrahedral meshes. At the beginning of each frame, we partition the set of equations governing the system using a randomized graph coloring algorithm. The unknowns in the equations belonging to the same partition are independent of each other. Then, all the equations belonging to the same partition are solved at the same time in parallel. Our algorithm runs completely on the GPU and can support changes in the constraints topology. We tested our method as a solver for soft body dynamics within the Projective Dynamics and Position Based Dynamics frameworks. We show how the algorithmic simplicity of this iterative strategy enables great numerical stability and fast convergence speed, which are essential features for physically based animations with fixed and small hard time budgets. Compared to the state of the art, we found our method to be faster and scale better while providing stabler solutions for very small time budgets.

Tangles are a form of structured pen-and-ink 2D art characterized by repeating, recursive patterns. We present a method to procedurally generate tangle drawings, seen as recursively split sets of arbitrary 2D polygons with holes, with anisotropic and non-stationary features. We formally model tangles with group grammars, an extension of set grammars, that explicitly handles the grouping of shapes necessary to represent tangle repetitions. We introduce a small set of expressive geometric and grouping operators, showing that they can respectively express complex tangles patterns and sub-pattern distributions, with relatively simple grammars. We also show how users can control tangle generation in an interactive and intuitive way. Throughout the paper, we show how group grammars can, in few tens of seconds, produce a wide variety of patterns that would take artists hours of tedious and time-consuming work. We then validated both the quality of the generated tangles and the efficiency of the control provided to the users with a user study, run with both expert and non-expert users.

Abstract We introduce a practical partitioning technique designed for parallelizing Position Based Dynamics, and exploiting the ubiquitous multi‐core processors present in current commodity GPUs. The input is a set of particles whose dynamics is influenced by spatial constraints. In the initialization phase, we build a graph in which each node corresponds to a constraint and two constraints are connected by an edge if they influence at least one common particle. We introduce a novel greedy algorithm for inserting additional constraints (phantoms) in the graph such that the resulting topology is ‐colourable, where is an arbitrary number. We color the graph, and the constraints with the same color are assigned to the same partition. Then, the set of constraints belonging to each partition is solved in parallel during the animation phase. We demonstrate this by using our partitioning technique; the performance hit caused by the GPU kernel calls is significantly decreased, leaving unaffected the visual quality, robustness and speed of serial position based dynamics.

Tracking multiple moving targets allows quantitative measure of the dynamic behavior in systems as diverse as animal groups in biology, turbulence in fluid dynamics and crowd and traffic control. In three dimensions, tracking several targets becomes increasingly hard since optical occlusions are very likely, i.e., two featureless targets frequently overlap for several frames. Occlusions are particularly frequent in biological groups such as bird flocks, fish schools, and insect swarms, a fact that has severely limited collective animal behavior field studies in the past. This paper presents a 3D tracking method that is robust in the case of severe occlusions. To ensure robustness, we adopt a global optimization approach that works on all objects and frames at once. To achieve practicality and scalability, we employ a divide and conquer formulation, thanks to which the computational complexity of the problem is reduced by orders of magnitude. We tested our algorithm with synthetic data, with experimental data of bird flocks and insect swarms and with public benchmark datasets, and show that our system yields high quality trajectories for hundreds of moving targets with severe overlap. The results obtained on very heterogeneous data show the potential applicability of our method to the most diverse experimental situations.

Mesh editing software is improving, allowing skilled artists to create detailed meshes efficiently. For a variety of reasons, artists are interested in sharing not just their final mesh but also their whole workflow, though the common media for sharing has limitations. In this paper, we present 3DFlow , an algorithm that computes continuous summarizations of mesh editing workflows. 3DFlow takes as input a sequence of meshes and outputs a visualization of the workflow summarized at any level of detail. The output is enhanced by highlighting edited regions and, if provided, overlaying visual annotations to indicated the artist's work, e.g. summarizing brush strokes in sculpting. We tested 3DFlow with a large set of inputs using a variety of mesh editing techniques, from digital sculpting to low-poly modeling, and found 3DFlow performed well for all. Furthermore, 3DFlow is independent of the modeling software used because it requires only mesh snapshots, and uses the additional information only for optional overlays. We release 3DFlow as open source for artists to showcase their work and release all our datasets so other researchers can improve upon our work.

Current modeling packages have polished interfaces for editing polygonal meshes, where artists work individually on each mesh. A variety of recent cloud-based services have shown the benefits of editing documents in real-time collaboration with others. In this paper, we present a system for collaborative editing of low-polygonal and subdivision mesh models. We cast collaborative editing as a special instance of distributed version control. We support concurrent editing by robustly sharing and merging mesh version histories in real-time. We store and transmit mesh differences efficiently by encoding them as sequences of primitive editing operations. We enable collaboration by merging and detecting conflicts. We extend this model letting artists adapt others' editing histories by retargeting sequences of editing operations to new parts of the mesh with potentially different topology. We tested our algorithms by editing meshes with up to thousand edits, in collaborative editing sessions lasting a few hours, and by retargeting sequences of several hundred edits. We found the proposed system to be reliable, fast and scaling well with mesh complexity. We demonstrate that our merge algorithm is more robust than prior work. We further validated the proposed collaborative workflow with a user study where MeshHisto was consistently preferred over other alternatives for collaborative workflows.

We present a thorough study to evaluate different light field editing interfaces, tools and workflows from a user perspective. This is of special relevance given the multidimensional nature of light fields, which may make common image editing tasks become complex in light field space. We additionally investigate the potential benefits of using depth information when editing, and the limitations imposed by imperfect depth reconstruction using current techniques. We perform two different experiments, collecting both objective and subjective data from a varied number of editing tasks of increasing complexity based on local point-and-click tools. In the first experiment, we rely on perfect depth from synthetic light fields, and focus on simple edits. This allows us to gain basic insight on light field editing, and to design a more advanced editing interface. This is then used in the second experiment, employing real light fields with imperfect reconstructed depth, and covering more advanced editing tasks. Our study shows that users can edit light fields with our tested interface and tools, even in the presence of imperfect depth. They follow different workflows depending on the task at hand, mostly relying on a combination of different depth cues. Last, we confirm our findings by asking a set of artists to freely edit both real and synthetic light fields.

Editing spatially-varying appearance is commonplace in most graphics applications. In this paper, we focus on materials whose appearance is described by BRDFs or BSSRDFs, with parameters specified by textures, and with local frame perturbations, namely bump, normal and tangent maps. Editing these materials amounts to editing the textures that encode the spatial variation. To perform these edits, artists commonly adopt imaging softwares since they have rich toolsets and well-understood user interfaces. But editing material parameters as images does not produce consistent results since the parameters' behaviours in their relative spaces are not taken in account. Our goal is to address this issue with a solution that is practical, in that we do not want to change material representation or editing workflow to ensure adoption. We observe that most image editing operations can be written as linear combination of colors. We thus define editing spaces for material parameters such that linear operations in these spaces respect their inherent meaning of the parameters. Transformations to and from editing spaces are non-linear to capture the non-linear behaviour of the parameters. Since GPUs are particularly efficient when executing linear operations, they can be used well with editing spaces. We demonstrate the use of editing spaces to edit microfacet BRDFs and SubEdit BSSRDFs by performing various imaging operations such as layering, linear and non-linear filtering, local and global contrast enhancements, and hardware-accelerated painting.

Thanks to its ability to improve the realism of computer-generated imagery, the use of global illumination has recently become widespread among digital lighting artists. It remains unclear, though, what impact it has on the lighting design workflows, especially for novice users. In this paper we present a user study which investigates the use of global illumination, large area lights, and non-physical fill lights in lighting design tasks, where 26 novice subjects design lighting with these tools. The collected data suggest that global illumination is not significantly harder to control for novice users that direct illumination, and when given the possibility, most users opt to use it in their designs. The use of global illumination together with large area lights leads to simpler lighting setups with fewer non-physical fill lights. Interestingly, global illumination does not supersede fill lights: users still include them into their globally illuminated lighting setups. We believe that our results will find use in the development of lighting design tools for non-expert users.

Abstract In this paper, we present EnvyDepth, an interface for recovering local illumination from a single HDR environment map. In EnvyDepth, the user quickly indicates strokes to mark regions of the environment map that should be grouped together in a single geometric primitive. From these annotated strokes, EnvyDepth uses edit propagation to create a detailed collection of virtual point lights that reproduce both the local and the distant lighting effects in the original scene. When compared to the sole use of the distant illumination, the added spatial information better reproduces a variety of local effects such as shadows, highlights and caustics. Without the effort needed to create precise scene reconstructions, EnvyDepth annotations take only tens of seconds to produce a plausible lighting without visible artifacts. This is easy to obtain even in the case of complex scenes, both indoors and outdoors. The generated lighting environments work well in a production pipeline since they are efficient to use and able to produce accurate renderings.

This paper presentsMeshGit, a practical algorithm for diffing and merging polygonal meshes typically used in subdivision modeling workflows. Inspired by version control for text editing, we introduce themesh edit distanceas a measure of the dissimilarity between meshes. This distance is defined as the minimum cost of matching the vertices and faces of one mesh to those of another. We propose an iterative greedy algorithm to approximate the mesh edit distance, which scales well with model complexity, providing a practical solution to our problem. We translate the mesh correspondence into a set of mesh editing operations that transforms the first mesh into the second. The editing operations can be displayed directly to provide a meaningful visual difference between meshes. For merging, we compute the difference between two versions and their common ancestor, as sets of editing operations. We robustly detect conflicting operations, automatically apply non-conflicting edits, and allow the user to choose how to merge the conflicting edits. We evaluateMeshGitby diffing and merging a variety of meshes and find it to work well for all.

Surfaces in the real world exhibit complex appearance due to spatial variations in both their reflectance and local shading frames (i.e. the local coordinate system defined by the normal and tangent direction). For opaque surfaces, existing fabrication solutions can reproduce well only the spatial variations of isotropic reflectance. In this paper, we present a system for fabricating surfaces with desired spatially-varying reflectance, including anisotropic ones, and local shading frames. We approximate each input reflectance, rotated by its local frame, as a small patch of oriented facets coated with isotropic glossy inks. By assigning different ink combinations to facets with different orientations, this bi-scale material can reproduce a wider variety of reflectance than the printer gamut, including anisotropic materials. By orienting the facets appropriately, we control the local shading frame. We propose an algorithm to automatically determine the optimal facets orientations and ink combinations that best approximate a given input appearance, while obeying manufacturing constraints on both geometry and ink gamut. We fabricate the resulting surface with commercially available hardware, a 3D printer to fabricate the facets and a flatbed UV printer to coat them with inks. We validate our method by fabricating a variety of isotropic and anisotropic materials with rich variations in normals and tangents.

Abstract We present an importance sampling method for the bidirectional scattering distribution function (bsdf) of hair. Our method is based on the multi‐lobe hair scattering model presented by Sadeghi et al. [ SPJT10 ]. We reduce noise by drawing samples from a distribution that approximates the bsdf well. Our algorithm is efficient and easy to implement, since the sampling process requires only the evaluation of a few analytic functions, with no significant memory overhead or need for precomputation. We tested our method in a research raytracer and a production renderer based on micropolygon rasterization. We show significant improvements for rendering direct illumination using multiple importance sampling and for rendering indirect illumination using path tracing.

We present a solution for viewing high dynamic range (HDR) images with spatially-varying distributions of glossy materials printed on reflective media. Our method exploits appearance variations of the glossy materials in the angular domain to display the input HDR image at different exposures. As viewers change the print orientation or lighting directions, the print gradually varies its appearance to display the image content from the darkest to the brightest levels. Our solution is based on a commercially available printing system and is fully automatic. Given the input HDR image and the BRDFs of a set of available inks, our method computes the optimal exposures of the HDR image for all viewing conditions and the optimal ink combinations for all pixels by minimizing the difference of their appearances under all viewing conditions. We demonstrate the effectiveness of our method with print samples generated from different inputs and visualized under different viewing and lighting conditions.

We propose a method for retargeting measured materials, where a source measured material is edited by applying the reflectance functions of a template measured dataset. The resulting dataset is a material that maintains the spatial patterns of the source dataset, while exhibiting the reflectance behaviors of the template. Compared to editing materials by subsequent selections and modifications, retargeting shortens the time required to achieve a desired look by directly using template data, just as color transfer does for editing images. With our method, users have to just mark corresponding regions of source and template with rough strokes, with no need for further input. This paper introduces AppWarp , an algorithm that achieves retargeting as a user-constrained, appearance-space warping operation, that executes in tens of seconds. Our algorithm is independent of the measured material representation and supports retargeting of analytic and tabulated BRDFs as well as BSSRDFs. In addition, our method makes no assumption of the data distribution in appearance-space nor on the underlying correspondence between source and target. These characteristics make AppWarp the first general formulation for appearance retargeting. We validate our method on several types of materials, including leaves, metals, waxes, woods and greeting cards. Furthermore, we demonstrate how retargeting can be used to enhance diffuse texture with high quality reflectance.

The construction of polygonal meshes remains a complex task in Computer Graphics, taking tens of thousands of individual operations over several hours of modeling time. The complexity of modeling in terms of number of operations and time makes it difficult for artists to understand all details of how meshes are constructed. We present MeshFlow , an interactive system for visualizing mesh construction sequences. MeshFlow hierarchically clusters mesh editing operations to provide viewers with an overview of the model construction while still allowing them to view more details on demand. We base our clustering on an analysis of the frequency of repeated operations and implement it using substituting regular expressions. By filtering operations based on either their type or which vertices they affect, MeshFlow also ensures that viewers can interactively focus on the relevant parts of the modeling process. Automatically generated graphical annotations visualize the clustered operations. We have tested MeshFlow by visualizing five mesh sequences each taking a few hours to model, and we found it to work well for all. We have also evaluated MeshFlow with a case study using modeling students. We conclude that our system provides useful visualizations that are found to be more helpful than video or document-form instructions in understanding mesh construction.

We present AppGen , an interactive system for modeling materials from a single image. Given a texture image of a nearly planar surface lit with directional lighting, our system models the detailed spatially-varying reflectance properties (diffuse, specular and roughness) and surface normal variations with minimal user interaction. We ask users to indicate global shading and reflectance information by roughly marking the image with a few user strokes, while our system assigns reflectance properties and normals to each pixel. We first interactively decompose the input image into the product of a diffuse albedo map and a shading map. A two-scale normal reconstruction algorithm is then introduced to recover the normal variations from the shading map and preserve the geometric features at different scales. We finally assign the specular parameters to each pixel guided by user strokes and the diffuse albedo. Our system generates convincing results within minutes of interaction and works well for a variety of material types that exhibit different reflectance and normal variations, including natural surfaces and man-made ones.

Recent work has shown that complex lighting effects can be well approximated by gathering the contribution of hundreds of thousands of virtual point lights (VPLs). This final gathering step is known as the many-lights problem. Due to the large number of VPLs, computing all the VPLs' contribution is not feasible. This paper presents LightSlice , an algorithm that efficiently solves the many-lights problem for large environments with complex lighting. As in prior work, we derive our algorithm from a matrix formulation of the many-lights problem, where the contribution of each VPL corresponds to a column, and computing the final image amounts to computing the sum of all matrix columns. We make the observation that if we cluster similar surface samples together, the slice of the matrix corresponding to these surface samples has significantly lower rank than the original matrix. We exploit this observation by deriving a two-step algorithm where we first globally cluster all lights, to capture the global structure of the matrix, and then locally refine these clusters to determine the most important lights for each slice. We then reconstruct a final image from only these locally-important lights. Compared to prior work, our algorithm has the advantage of discovering and exploiting the global as well as local matrix structure, giving us a speedup of between three and six times compared to state-of-the-art algorithms.

Abstract This paper presents an image editing framework where users use reference images to indicate desired color edits. In our approach, users specify pairs of strokes to indicate corresponding regions in both the original and the reference image that should have the same color “style”. Within each stroke pair, a nonlinear constrained parametric transfer model is used to transfer the reference colors to the original. We estimate the model parameters by matching color distributions, under constraints that ensure no visual artifacts are present in the transfer result. To perform transfer on the whole image, we employ optimization methods to propagate the model parameters defined at each stroke location to spatially‐close regions of similar appearance. This stroke‐based formulation requires minimal user effort while retaining the high degree of user control necessary to allow artistic interpretations. We demonstrate our approach by performing color transfer on a number of image pairs varying in content and style, and show that our algorithm outperforms state‐of‐the‐art color transfer methods on both user‐controllability and visual qualities of the transfer results.

Abstract In computer cinematography, artists routinely use non‐physical lighting models to achieve desired appearances. This paper presentsBendyLights, a non‐physical lighting model where light travels nonlinearly along splines, allowing artists to control light direction and shadow position at different points in the scene independently. Since the light deformation is smoothly defined at all world‐space positions, the resulting non‐physical lighting effects remain spatially consistent, avoiding the frequent incongruences of many non‐physical models.BendyLightsare controlled simply by reshaping splines, using familiar interfaces, and require very few parameters.BendyLightcontrol points can be keyframed to support animated lighting effects. We demonstrateBendyLightsboth in a realtime rendering system for editing and a production renderer for final rendering, where we show thatBendyLightscan also be used with global illumination.

Abstract We present an approach for editing shadows in all‐frequency lighting environments. To support artistic control, we propose to decouple shadowing from lighting and focus on providing intuitive controls to edit the former. To accomplish this task, we precompute and store scene visibility information separately from lighting and BRDFs and allow artists to edit visibility directly, by providing operations to select shadows and edit their shape. To facilitate a wider range of editing operations, we generalize visibility from binary to three‐channel oating point quantities and introduce a novel shadow representation based on computation of visibility ratios between the original render and the edited one. We demonstrate our results for diffuse and glossy surfaces, still scenes and animations.

Abstract Historically, rendering system development has been mainly focused on improving the numerical accuracy of the rendering algorithms and their runtime efficiency. In this paper, we propose a method to improve the correctness not of the algorithms themselves, but of their implementation. Specifically, we show that by combining static type checking and generic programming, rendering system and shader development can take advantage of compile‐time checking to perform dimensional analysis, i.e. to enforce the correctness of physical dimensions and units in light transport, and geometric space analysis, i.e. to ensure that geometric computations respect the spaces in which points, vectors and normals were defined. We demonstrate our methods by implementing a CPU path tracer and a GPU renderer which previews direct illumination. While we build on prior work to develop our implementations, the main contribution of our work is to show that dimensional analysis and geometric space checking can be successfully integrated into the development of rendering systems and shaders.

Many real world surfaces exhibit translucent appearance due to subsurface scattering. Although various methods exists to measure, edit and render subsurface scattering effects, no solution exists for manufacturing physical objects with desired translucent appearance. In this paper, we present a complete solution for fabricating a material volume with a desired surface BSSRDF. We stack layers from a fixed set of manufacturing materials whose thickness is varied spatially to reproduce the heterogeneity of the input BSSRDF. Given an input BSSRDF and the optical properties of the manufacturing materials, our system efficiently determines the optimal order and thickness of the layers. We demonstrate our approach by printing a variety of homogenous and heterogenous BSSRDFs using two hardware setups: a milling machine and a 3D printer.

Material design is the process by which artists specify the reflectance properties of a surface, such as its diffuse color and specular roughness. We present a user study to evaluate the relative benefits of different material design interfaces, focusing on novice users since they stand to gain the most from intuitive interfaces. Specifically, we investigate the editing of the parameters of analytic bidirectional distribution functions (BRDFs) using three interface paradigms: physical sliders by which users set the parameters of analytic BRDF models, such as diffuse albedo and specular roughness; perceptual sliders by which users set perceptually-inspired parameters, such as diffuse luminance and gloss contrast; and image navigation by which material variations are displayed in arrays of image thumbnails and users make edits by selecting them. We investigate two design tasks: precise adjustment and artistic exploration. We collect objective and subjective data, finding that subjects can perform equally well with physical and perceptual sliders as long as the interface responds interactively. Image navigation performs worse than the other interfaces on precise adjustment tasks, but excels at aiding in artistic exploration. We find that given enough time, novices can perform relatively complex material editing tasks with little training, and most novices work similarly to one another.

Scenes lit with high dynamic range environment maps of real-world environments exhibit all the complex nuances of natural illumination. For applications that need lighting adjustments to the rendered images, editing environment maps directly is still cumbersome. First, designers have to determine which region in the environment map is responsible for the specific lighting feature (e.g. diffuse gradients, highlights and shadows) they desire to edit. Second, determining the parameters of image-editing operations needed to achieve specific changes to the selected lighting feature requires extensive trial-and-error. This paper presents envyLight , an interactive interface for editing natural illumination that combines an algorithm to select environment map regions, by sketching strokes on lighting features in the rendered image, with a small set of editing operations to quickly adjust the selected feature. The envyLight selection algorithm works well for indoor and outdoor lighting corresponding to rendered images where lighting features vary widely in number, size, contrast and edge blur. Furthermore, envyLight selection is general with respect to material type, from matte to sharp glossy, and the complexity of scenes' shapes. envyLight editing operations allow designers to quickly alter the position, contrast and edge blur of the selected lighting feature and can be keyframed to support animation.

Lighting design is a complex but fundamental task in computer cinematography, involving the adjustment of light parameters to define final scene appearance. Many user interfaces have been proposed to simplify lighting design. They can be generally categorized in three paradigms: direct light parameter manipulation, indirect light feature manipulation (e.g., shadow dragging), and goal-based optimization of lighting through painting. To this date, no formal evaluation of the relative effectiveness of these paradigms has been performed. In this paper, we present a first step toward evaluating the benefits of these three paradigms in the form of a user study with a focus on novice users. 20 subjects participated in the experiment by performing various trials on simple scenes with up to 8 point lights, designed to test two lighting tasks: precise adjustment of lighting and the artistic exploration of lighting configurations. We collected objective and subjective data and found that subjects can light well with direct and indirect interfaces, preferring the latter. Paint-based goal specification was found to be significantly worse than the other paradigms, especially since users tend to sketch rather than accurately paint goal images, an input that painting algorithms were not designed for. We also found that given enough time, novices can perform relatively complex lighting tasks, unhindered by geometry or lighting complexity. Finally, we believe that our study will impact the design of future lighting interfaces and it will serve as the basis for designing additional experiments to reach a comprehensive evaluation of lighting interfaces.

Although real-world surfaces can exhibit significant variation in materials --- glossy, diffuse, metallic, etc. --- printers are usually used to reproduce color or gray-scale images. We propose a complete system that uses appropriate inks and foils to print documents with a variety of material properties. Given a set of inks with known Bidirectional Reflectance Distribution Functions (BRDFs), our system automatically finds the optimal linear combinations to approximate the BRDFs of the target documents. Novel gamut-mapping algorithms preserve the relative glossiness between different BRDFs, and halftoning is used to produce patterns to be sent to the printer. We demonstrate the effectiveness of this approach with printed samples of a number of measured spatially-varying BRDFs.

In this paper we present SubEdit , a representation for editing the BSSRDF of heterogeneous subsurface scattering acquired from real-world samples. Directly editing measured raw data is difficult due to the non-local impact of heterogeneous subsurface scattering on the appearance. Our SubEdit representation decouples these non-local effects into the product of two local scattering profiles defined at respectively the incident and outgoing surface locations. This allows users to directly manipulate the appearance of single surface locations and to robustly make selections. To further facilitate editing, we reparameterize the scattering profiles into the local appearance concepts of albedo, scattering range, and profile shape. Our method preserves the visual quality of the measured material after editing by maintaining the consistency of subsurface transport for all edits. SubEdit fits measured data well while remaining efficient enough to support interactive rendering and manipulation. We illustrate the suitability of SubEdit as a representation for editing by applying various complex modifications on a wide variety of measured heterogeneous subsurface scattering materials.

Abstract Rendering animations of scenes with deformable objects, camera motion, and complex illumination, including indirect lighting and arbitrary shading, is a long‐standing challenge. Prior work has shown that complex lighting can be accurately approximated by a large collection of point lights. In this formulation, rendering of animation sequences becomes the problem of efficiently shading many surface samples from many lights across several frames. This paper presents a tensor formulation of the animated many‐light problem, where each element of the tensor expresses the contribution of one light to one pixel in one frame. We sparsely sample rows and columns of the tensor, and introduce a clustering algorithm to select a small number of representative lights to efficiently approximate the animation. Our algorithm achieves efficiency by reusing representatives across frames, while minimizing temporal flicker. We demonstrate our algorithm in a variety of scenes that include deformable objects, complex illumination and arbitrary shading and show that a surprisingly small number of representative lights is sufficient for high quality rendering. We believe out algorithm will find practical use in applications that require fast previews of complex animation.

Abstract 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.

Abstract This article surveys the use of eye tracking in investigations of online search. Three eye tracking experiments that we undertook are discussed and compared to additional work in this area, revealing recurring behaviors and trends. The first two studies are described in greater detail in Granka, Joachims, & Gay (2004), Lorigo et al. (2006), and Pan et al. (2007), and the third study is described for the first time in this article. These studies reveal how users view the ranked results on a search engine results page (SERP), the relationship between the search result abstracts viewed and those clicked on, and whether gender, search task, or search engine influence these behaviors. In addition, we discuss a key challenge that arose in all three studies that applies to the use of eye tracking in studying online behaviors which is due to the limited support for analyzing scanpaths, or sequences of eye fixations. To meet this challenge, we present a preliminary approach that involves a graphical visualization to compare a path with a group of paths. We conclude by summarizing our findings and discussing future work in further understanding online search behavior with the help of eye tracking.

We present an intuitive and efficient method for editing the appearance of complex spatially-varying datasets, such as images and measured materials. In our framework, users specify rough adjustments that are refined interactively by enforcing the policy that similar edits are applied to spatially-close regions of similar appearance. Rather than proposing a specific user interface, our method allows artists to quickly and imprecisely specify the initial edits with any method or workflow they feel most comfortable with. An energy optimization formulation is used to propagate the initial rough adjustments to the final refined ones by enforcing the editing policy over all pairs of points in the dataset. We show that this formulation is equivalent to solving a large linear system defined by a dense matrix. We derive an approximate algorithm to compute such a solution interactively by taking advantage of the inherent structure of the matrix. We demonstrate our approach by editing images, HDR radiance maps, and measured materials. Finally, we show that our framework generalizes prior methods while providing significant improvements in generality, robustness and efficiency.

We present an efficient computational algorithm for functions represented by a nonlinear piecewise constant approximation called cuts. Our main contribution is a single traversal algorithm for merging cuts that allows for arbitrary pointwise computation, such as addition, multiplication, linear interpolation, and multi-product integration. A theoretical error bound of this approach can be proved using a statistical interpretation of cuts. Our algorithm extends naturally to computation with many cuts and maps easily to modern GPUs, leading to significant advantages over existing methods based on wavelet approximation. We apply this technique to the problem of realistic lighting and material design under complex illumination with arbitrary BRDFs. Our system smoothly integrates all-frequency relighting of shadows and reflections with dynamic per-pixel shading effects, such as bump mapping and spatially varying BRDFs. This combination of capabilities is typically missing in current systems. We represent illumination and precomputed visibility as nonlinear sparse vectors; we then use our cut merging algorithm to simultaneously interpolate visibility cuts at each pixel, and compute the triple product integral of the illumination, interpolated visibility, and dynamic BRDF samples. Finally, we present a two-pass, data-driven approach that exploits pilot visibility samples to optimize the construction of the light tree, leading to more efficient cuts and reduced datasets.

Abstract The authors present results from a real‐world study depicting remote collaboration trends of a community of more than 87,000 scientists over 30 years. They utilize publication records of more than 200,000 scholarly journal articles, together with affiliations of the authors to infer distance collaborations. The longevity of their study is of interest because it covers several years before and after the birth of the Internet and computer‐supported collaborative work (CSCW) technologies. Thus, they provide one lens through which the impact of computer‐assisted collaborative work technologies can be viewed. Their results show that there has been a steady and constant growth in the frequency of both interinstitute and cross‐country collaborations in a particular physics domain, regardless of the introduction of these technologies. This suggests that we are witnessing an evolution, rather than a revolution, with respect to long‐distance collaborative behavior. An interdisciplinary approach, combining numerical statistics, graph visualizations, and social network measurements, facilitates their remarks on the changes in the size and structure of these collaborations over this period of history.

Rendering complex scenes with indirect illumination, high dynamic range environment lighting, and many direct light sources remains a challenging problem. Prior work has shown that all these effects can be approximated by many point lights. This paper presents a scalable solution to the many-light problem suitable for a GPU implementation. We view the problem as a large matrix of sample-light interactions; the ideal final image is the sum of the matrix columns. We propose an algorithm for approximating this sum by sampling entire rows and columns of the matrix on the GPU using shadow mapping. The key observation is that the inherent structure of the transfer matrix can be revealed by sampling just a small number of rows and columns. Our prototype implementation can compute the light transfer within a few seconds for scenes with indirect and environment illumination, area lights, complex geometry and arbitrary shaders. We believe this approach can be very useful for rapid previewing in applications like cinematic and architectural lighting design.

Lighting is a fundamental aspect of computer cinematography that involves the placement and configuration of lights to establish mood and enhance storytelling. This process is labor intensive as artists repeatedly adjust the parameters of a large set of complex lights to achieve a desired effect. Typical lighting controls affect the final image indirectly, requiring a large number of trials to obtain a suitable result. We present an interactive system wherein an artist paints desired lighting effects directly into the scene, and the computer solves for parameters that achieve the desired look. The artist can paint color, light shape, shadows, highlights, and reflections using a suite of tools designed for painting light. Our system matches these effects using a nonlinear optimizer made robust by a combination of initial estimates, system design, and user-guided optimization. In contrast, previous work on painting light has not permitted the lights to move, allowing for linear optimization but preventing its use in computer cinematography. To demonstrate our approach we lit several scenes, mainly using a direct illumination renderer designed for computer animation, but also including two other rendering styles. We show that painting interfaces can quickly produce high quality lighting setups, easing the lighting artist's workflow.

We investigate a new approach to editing spatially- and temporally-varying measured materials that adopts a stroke-based workflow. In our system, a user specifies a small number of editing constraints with a 3-D painting interface which are smoothly propagated to the entire dataset through an optimization that enforces similar edits are applied to areas with similar appearance. The sparse nature of this appearance-driven optimization permits the use of efficient solvers, allowing the designer to interactively refine the constraints. We have found this approach supports specifying a wide range of complex edits that would not be easy with existing techniques which present the user with a fixed segmentation of the data. Furthermore, it is independent of the underlying reflectance model and we show edits to both analytic and non-parametric representations in examples from several material databases.

This paper presents an interactive GPU-based system for cinematic relighting with multiple-bounce indirect illumination from a fixed view-point. We use a deep frame-buffer containing a set of view samples, whose indirect illumination is recomputed from the direct illumination on a large set of gather samples, distributed around the scene. This direct-to-indirect transfer is a linear transform which is particularly large, given the size of the view and gather sets. This makes it hard to precompute, store and multiply with. We address this problem by representing the transform as a set of sparse matrices encoded in wavelet space. A hierarchical construction is used to impose a wavelet basis on the unstructured gather cloud, and an image-based approach is used to map the sparse matrix computations to the GPU. We precompute the transfer matrices using a hierarchical algorithm and a variation of photon mapping in less than three hours on one processor. We achieve high-quality indirect illumination at 10-20 frames per second for complex scenes with over 2 million polygons, with diffuse and glossy materials, and arbitrary direct lighting models (expressed using shaders). We compute per-pixel indirect illumination without the need of irradiance caching or other subsampling techniques.

Programmable shading is a fundamental technique for specifying appearance in 3d environments. While shading architectures provides fast execution of shaders, shader evaluation is today a major cost in the rendering process. In the same manner in which geometric simplification lets us deal with large models, it would be beneficial to have an automatic technique that trades off shader quality for speed.This paper presents such a technique by introducing a framework for the automatic simplification of complex procedural shaders, where a sequence of increasingly simplified shaders is generated starting from an original shader together with ranges for all of its input parameters. Our approach works by applying simplification rules to the code of a shader to generate a series of candidates, whose differences from the original one are measured and used to select the candidate with the smallest error. This procedure is repeated until the last shader is a constant. While this automatic procedure generates high quality simplified shaders, the artist might want to emphasize particular aspects of a shader during simplification. Our framework supports this desire by allowing the user to specify additional rules to be considered during simplification. The term user-configurable simplification comes from this feature of our system.We implemented our algorithm to support the simplification of fragment shaders running on graphics hardware. Our results show that automatic simplification of complex procedural shaders is possible with high quality.

In computer cinematography, the process of lighting design involves placing and configuring lights to define the visual appearance of environments and to enhance story elements. This process is labor intensive and time consuming, primarily because lighting artists receive poor feedback from existing tools: interactive previews have very poor quality, while final-quality images often take hours to render.This paper presents an interactive cinematic lighting system used in the production of computer-animated feature films containing environments of very high complexity, in which surface and light appearances are described using procedural RenderMan shaders. Our system provides lighting artists with high-quality previews at interactive framerates with only small approximations compared to the final rendered images. This is accomplished by combining numerical estimation of surface response, image-space caching, deferred shading, and the computational power of modern graphics hardware.Our system has been successfully used in the production of two feature-length animated films, dramatically accelerating lighting tasks. In our experience interactivity fundamentally changes an artist's workflow, improving both productivity and artistic expressiveness.

In this paper we introduce a new approach to realistic rendering at interactive rates on commodity graphics hardware. The approach uses efficient perceptual metrics within a decision theoretic framework to optimally order rendering operations, producing images of the highest visual quality within system constraints. We demonstrate the usefulness of this approach for various applications such as diffuse texture caching, environment map prioritization and radiosity mesh simplification. Although here we address the problem of realistic rendering at interactive rates, the perceptually-based decision theoretic methodology we introduce can be usefully applied in many areas of computer graphics.

This paper introduces a new kind of mosaic, called Jigsaw Image Mosaic (JIM), where image tiles of arbitrary shape are used to compose the final picture. The generation of a Jigsaw Image Mosaic is a solution to the following problem: given an arbitrarily-shaped container image and a set of arbitrarily-shaped image tiles, fill the container as compactly as possible with tiles of similar color to the container taken from the input set while optionally deforming them slightly to achieve a more visually-pleasing effect. We approach the problem by defining a mosaic as the tile configuration that minimizes a mosaicing energy function. We introduce a general energy-based framework for mosaicing problems that extends some of the existing algorithms such as Photomosaics and Simulated Decorative Mosaics. We also present a fast algorithm to solve the mosaicing problem at an acceptable computational cost. We demonstrate the use of our method by applying it to a wide range of container images and tiles.

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.

In this paper, we present a system for interactive computation of global illumination in dynamic scenes. Our system uses a novel scheme for caching the results of a high quality pixel-based renderer such as a bidirectional path tracer. The Shading Cache is an object-space hierarchical subdivision mesh with lazily computed shading values at its vertices. A high frame rate display is generated from the Shading Cache using hardware-based interpolation and texture mapping. An image space sampling scheme refines the Shading Cache in regions that have the most interpolation error or those that are most likely to be affected by object or camera motion.Our system handles dynamic scenes and moving light sources efficiently, providing useful feedback within a few seconds and high quality images within a few tens of seconds, without the need for any pre-computation. Our approach allows us to significantly outperform other interactive systems based on caching ray-tracing samples, especially in dynamic scenes. Based on our results, we believe that the Shading Cache will be an invaluable tool in lighting design and modelling while rendering.

In this paper we introduce a new light reflection model for image synthesis based on experimental studies of surface gloss perception. To develop the model, we've conducted two experiments that explore the relationships between the physical parameters used to describe the reflectance properties of glossy surfaces and the perceptual dimensions of glossy appearance. In the first experiment we use multidimensional scaling techniques to reveal the dimensionality of gloss perception for simulated painted surfaces. In the second experiment we use magnitude estimation methods to place metrics on these dimensions that relate changes in apparent gloss to variations in surface reflectance properties. We use the results of these experiments to rewrite the parameters of a physically-based light reflection model in perceptual terms. The result is a new psychophysically-based light reflection model where the dimensions of the model are perceptually meaningful, and variations along the dimensions are perceptually uniform. We demonstrate that the model can facilitate describing surface gloss in graphics rendering applications. This work represents a new methodology for developing light reflection models for image synthesis.