Smooth Shading Research Articles

Viewpoint-dependent lighting on polygonal holograms using bump mapping.

Holograms can be observed from different viewpoints, because light waves can be encoded to propagate in multiple directions. Thus, accurate holograms for 3D display should model viewpoint-dependent light reflections. We proposed a new, to the best of our knowledge, hologram generation method for objects represented by polygonal meshes, whose lighting changes as the viewer moves, all while rendering smooth shading using low-poly objects. The proposed method leverages bump mapping and converts it into a bump-phase map encoding the propagation frequency and then spreads the reflected light wave so that only a specific viewpoint can receive them. Simulation experiments with small pixel pitches confirm the method's high computational performance.

Improving the noise immunity of 3D computational ghost imaging.

Computational ghost imaging (CGI) can build a three-dimensional (3D) image using the reconstructed shading images. However, it could be easily affected by the noise accumulated in the 3D reconstruction. More importantly, the selection of initial growing position will also affect the quality of the formed 3D image significantly. In this paper, we apply the technique of sub-pixel displacement to achieve smooth shading images in noisy environments and propose a method for selecting the optimal initial growing position to preserve the stereo feature of the object. We demonstrate that the surfaces of the reconstructed 3D images are more accurate using our proposed method as compared to the ones achieved by previously used methods. Our research would promote the development of 3D imaging using CGI in noisy environments.

Intrinsic Image Decomposition with Step and Drift Shading Separation.

Decomposing an image into the shading and reflectance layers remains challenging due to its severely under-constrained nature. We present an approach based on illumination decomposition that recovers the intrinsic images without additional information, e.g., depth or user interaction. Our approach is based on the rationale that the shading component contains the step and drift channels simultaneously. We decompose the illumination into two channels: the step shading, corresponding to the sharp shading changes due to cast shadow or abrupt shape changes; the drift shading, accounting for the smooth shading variations due to gradual illumination changes or slow shape changes. Due to such transformation of turning the conventional assumption that shading has smoothness as reasonable prior, our model has the advantages in handling real images, especially with the cast shadows or strong shape edges. We also apply a much stricter edge classifier along with a reinforcement process to enhance our method. We formulate the problem using a two-parameter energy function and split it into two energy functions corresponding to the reflectance and step shading. Experiments on the MIT dataset, the IIW dataset and the MPI Sintel dataset have shown the success of our approach over the state-of-the-art methods.

An enhanced filtering-based approach to approximate volumetric ambient occlusion

Achieving, through shading, a good visualisation of scientific volumetric data sets is prohibitive for interactive applications due to a significant amount of existing occlusion effects and lighting variation. Ambient occlusion, although allowing us to understand these data through soft shadows, often comes with an important cost of pre-processing which prevents its use especially in the applications based on the transfer function editing. In this paper, we present a new method for approximating ambient occlusion for volumetric data using an exponential function which allows for high-quality hardware-accelerated filtering and leads us to achieve more compact information using a filterable representation in order to avoid the classic occlusion test with a binary manner. Our evaluation of a series of medical images demonstrates that the proposed algorithm provides smooth shading, producing high quality results, achieves an interactive rate and consumes less memory.

An enhanced filtering-based approach to approximate volumetric ambient occlusion

Achieving, through shading, a good visualisation of scientific volumetric data sets is prohibitive for interactive applications due to a significant amount of existing occlusion effects and lighting variation. Ambient occlusion, although allowing us to understand these data through soft shadows, often comes with an important cost of pre-processing which prevents its use especially in the applications based on the transfer function editing. In this paper, we present a new method for approximating ambient occlusion for volumetric data using an exponential function which allows for high-quality hardware-accelerated filtering and leads us to achieve more compact information using a filterable representation in order to avoid the classic occlusion test with a binary manner. Our evaluation of a series of medical images demonstrates that the proposed algorithm provides smooth shading, producing high quality results, achieves an interactive rate and consumes less memory.

Highlight disparities contribute to perceived depth of shiny 3D surface

When a shiny surface is viewed binocularly, the specular highlights have different disparities than points on the surface. This study tested whether conflicting highlight disparities contribute to perception of surface shape when other shape cues are available. A recent study by Muryy et al (2013) found that perceived shape followed highlight disparities for mirrored surfaces, but not for surfaces with texture or shading. Is stereo information from highlights overridden by additional surface information, or is there still an influence on quantitative perceived shape? To test this, I varied the depth of specular highlights relative to a surface and measured the effect on perceived extent in depth. Subjects viewed stereo images of elliptical bumps with a flat frontal rim, with varied height and curvature, and estimated height of the bump. Surfaces had smooth shading with and without highlights, and highlights were either accurate or shifted in depth. Simulated illumination was a grid of light fixtures, which was translated and scaled to control the image position of highlights. Surfaces had either high contrast texture or very low contrast texture to vary the quality of surface disparity information. With high contrast texture, highlight disparities did not influence depth estimates. The presence of highlights produced an overall increase in perceived depth, but varying the depth of highlights had no effect. With low contrast texture, depth estimates were strongly influenced by highlight disparities. The presence of highlights improved accuracy, and varying the depth of highlights produced corresponding changes in depth estimates. The effect was the same whether the highlights were consistent or inconsistent with smooth shading. The results demonstrate that binocular highlights can influence perceived shape when other surface information is available but weak. This suggests that highlight disparities are perceptually integrated despite providing conflicting information Meeting abstract presented at VSS 2017

A moving object and observers in ℝ2 with a piecewise smooth shading set

We consider the motion of an object t in the space ℝ2, where a bodily bounded set G with piecewise smooth boundary hinders the motion and visibility. In a neighborhood of convex parts of the boundary, there are observers, which can hide from t in a shading set s(t) ⊂ ℝ2G in the case of danger from t. We find characteristic properties of a trajectory T of the object that maximizes the value min{ρ(t, s(t)): t ∈ T}.

Simple wave-field rendering for photorealistic reconstruction in polygon-based high-definition computer holography

A simple and practical technique is presented for creating fine three-dimensional (3D) images with polygon-based computer-generated holograms. The polygon-based method is a technique for computing the optical wave-field of virtual 3D scenes given by a numerical model. The presented method takes less computation time than common point-source methods and produces fine spatial 3D images of deep 3D scenes that convey a strong sensation of depth, unlike conventional 3D systems providing only binocular disparity. However, smooth surfaces cannot be reconstructed using the presented method because the surfaces are approximated by planar polygons. This problem is resolved by introducing a simple rendering technique that is almost the same as that in common computer graphics, since the polygon-based method has similarity to rendering techniques in computer graphics. Two actual computer holograms are presented to verify and demonstrate the proposed technique. One is a hologram of a live face whose shape is measured using a 3D laser scanner that outputs polygon-mesh data. The other is for a scene including the moon. Both are created employing the proposed rendering techniques of the texture mapping of real photographs and smooth shading.

Perceiving Direction of a Walker: Effect of Body Appearance

Human can perceive others' walking direction accurately even with 117ms observation (Sato, et al., ECVP2008). We aimed to see whether appearance of walker's body affects the accuracy of perceiving direction of the walker. Thus, we employed three different appearances: realistic human computer-graphics body (CG-human), nonrealistic cylinder-assembled body (Cylinders), and point-light walker (Points). We made a three-dimensional model of an adult-size walker who walked at a place. CG-human stimuli were generated by rendering the model with smooth shading. We made Cylinders stimuli by replacing body parts such as arms, legs, head, and hands with cylinders. Points stimuli were made by tracking 18 positions (mostly joints) of the body like biological motion. One of walkers was presented for 117, 250, 500 or 1000ms while its direction was randomly varied by 3deg steps to 21deg left or right. Observers judged whether the walker was walking toward them (hit) or not (miss), and self-range was measured in terms of the standard deviation for hit distributions. The perceived self-range was narrowed with long duration, and with CG-human stimulus. It is suggested that the accuracy of perceiving walker's direction depends on body appearance, and it is higher for human-like body than nonhuman body.

Volumetric ambient occlusion for volumetric models

This paper presents new algorithms to compute ambient occlusion for volumetric data. Ambient occlusion is used in video-games and film animation to mimic the indirect lighting of global illumination. We extend a novel interpretation of ambient occlusion to volumetric models that measures how big portion of the tangent sphere of a surface belongs to the set of occluded points, and propose statistically robust estimates for the ambient occlusion value. The data needed by this estimate can be obtained by separable filtering of the voxel array. As ambient occlusion is meant to obtain global illumination effects, it can provide decisive clues in interpreting the data. The new algorithms obtain smooth shading and can be computed at interactive rates, being thus appropriate for dynamic models exploration.

Algorithm 834

We describe an interactive surface visualization tool implemented in C, OpenGL, and GLUT. The surface is represented by a set of triangles in Euclidean 3-space, thus allowing for unrestricted topology. Capabilities include color-filled contour plots (for the graph of a bivariate function) and surface perspective plots with lighting and smooth shading. Interactive zooms and axis rotations are executed with a single keypress or mouse motion. The advantage of this code over the many alternatives is that it is small, simple, portable, easy to install and use, and the source code is available if the user wishes to change defaults, add light sources, or whatever.

Incremental update of computer-generated holograms

We describe the incremental computing method for making localized changes to a computer-generated hologram to rapidly modify the 3-D image it reconstructs. The method populates a scene with holo- graphic primitives, tracks scene-based changes, and updates the diffrac- tive contributions of only affected primitives. Changes are rapidly incor- porated into the hologram via simple arithmetic operations, and only affected regions of the hologram are updated at each simulation time step. The method can accommodate different holographic primitive rep- resentations, is designed to be suitable for hardware assistance, and is also compatible with computer-graphics-style techniques for smooth shading, texture mapping, and reflections. © 2003 Society of Photo-Optical In-

Choosing rendering parameters for effective communication of 3D shape

We conducted a series of perceptual experiments to assess the contributions of rendering parameters to the perception of the shape of three-dimensional objects. For the experiments, observers viewed graphically rendered displays consisting of pairs of rotating objects and judged whether their shapes were identical. For some pairs they were, while for other pairs they differed by varying amounts. We determined the accuracy of shape perception from these discrimination judgments. We provide background information for the operational definition of shape used throughout the experiments, as well as for the rendering factors under experimental investigation: occluding contour, smooth shading, and specular highlights. Following that, we describe a series of experiments. Experiment 1 demonstrated the effectiveness of our new technique for the exploration of perceptual issues related to graphic interfaces. An additional four experiments produced results concerning the effects of rendering parameters on the communication of 3D shape. Experiments 2 and 3 investigated the contributions of basic rendering conditions such as the presence of occluding contours and smooth surface shading. In Experiments 4 and 5, the manipulation of specular highlighting revealed that accurate shape discrimination judgments were possible either with or without the specular component. These results lay a foundation for reasoned manipulation of interface properties when accurate communication of 3D shape is a primary goal of the display.

A hardware architecture for video rate smooth shading of volume data

This paper describes a new architecture for generating smoothly shaded two dimensional images of volume data. This architecture fits into an image synthesis pipeline and uses only simple arithmetic operations and a look-up table to generate 2-D images in real time. The shading algorithm is an extension of the grey-level gradient algorithm for shading volume data. The shading technique produces smooth images for voxelized geometrical data and sampled volume data. Image synthesis from volume data in real time is an important technique in visualization and graphics systems.

Segmented transducer design using an optimum mean square quantizer approach

This article describes an approach to acoustic transducer design that results in the construction of transducers with desirable radiation patterns. The radiation pattern from a uniformly excited transducer has, for many applications, unacceptably high sidelobes. A smoothly shaded transducer, e.g., one with Gaussian or Blackman-Harris shading, has better sidelobe structure but may be difficult to construct accurately. Segmented transducers, where each segment is excited uniformly, can be used to approximate a smooth shading in a stepwise fashion. The optimum mean square quantizer approach is presented in this article as a method for rationally choosing segment sizes and excitation levels. As implied by the name, the method minimizes the mean square error between a desired smooth shading and an L level segmented approximation to it. Both the sizes and the amplitude levels of the elements are allowed to vary, permitting better performance for a fixed number of elements than might be achievable for the same number of equisized elements. The method is developed in this article for two one-dimensional cases: The linear segmented transducer, and the radially symmetric segmented transducer. The method is demonstrated through the design of a three-level radially symmetric segmented transducer that generates a close approximation to a Gaussian beam.

Illuminating the fourth dimension

A family of techniques for creating intuitively informative shaded images of 4-D mathematical objects is proposed. The rendering of an object in a 4-D world is described by considering step-by-step how objects might be rendered into images in simpler worlds. The mathematical principles needed to compute projected images of objects and their shadows in D dimensions are outlined. The issues involved in producing shaded images of objects in four dimensions, including extending rendering from 3-D to 4-D, smooth shading, and specularity, are discussed. Results of rendering a Steiner surface, torus, and knotted sphere in four dimensions are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A speedy voxel-tracing method for cutting solid display of 3-D images

This paper describes a high-speed image-generation method which arbitrarily cuts out a three-dimensional (3-D) digital object (3-D image) in a 3-D frame memory and three-dimensionally displays its internal shape realistically. The idea of ray-tracing is applied to a 3-D memory space so that a high-speed ray-tracing is carried out in it by using a 3-D digital differential analyzer (DDA) called the reversible step type. To obtain cross points of a ray (straight line) and an object in a 3-D frame memory, an algorithm indicating address orders of all the voxels through which the ray passes is shown. A viewpoint of obtaining a realistic 3-D representation with a smooth surface from an irregular digital surface, calculation method of normal vector is important. A new factor, “existential density,” which can be obtained by a simple calculation around the surface of the digital object, is introduced; and a method to obtain a normal vector from this factor using the distribution of density gradient also is described. Since this calculation requires 3 × 3 × 3 operators, addition/ subtraction of integers and shift operations, the operation is high speed and suitable for hardware. The proposed algorithm is confirmed by a computer simulation which produces 3-D images with smooth shading.

Faster Phong Shading via Angular Interpolation

AbstractOne of the most successful algorithms that brought realism to the world of 3D image generation is Phong shading. It is an algorithm for smooth shading meshes of planar polygons used to represent curved surfaces. The level of realism and depth perception that can be obtained by Phong shading is attractive for 3D CAD applications and related areas. However, per pixel computation costs which were too high and/or artifacts, introduced by some of the more efficient evaluation methods and apparent only when displaying moving objects, are major factors mat blocked the common usage of Phong shading in highly interactive applications.In this paper we present angular interpolation for Phong shading planar polygons. Angular interpolation was a method especially designed to meet requirements as imposed by special purpose hardware we developed1, but turned out to be generally applicable. The angular interpolation method appears to be very efficient and reduces artifacts when displaying moving objects. Ideally a shading algorithm imposes no need for subdivision of patches as presented by the solid modelling system. Shading calculation via angular interpolation yields such an ideal algorithm. We will describe two alternative evaluation methods that trade off evaluation cost against level of accuracy. They both can handle light source and view point at arbitrary distances, but differ in level of accuracy. As a consequence these alternative evaluation methods do impose restrictions on the topology of patches and light sources. However, generally, the limitations imposed by these alternative shading methods are much more liberal than the limitations on patch size imposed by the geometry.The most economic evaluation method we present can incrementally compute the colour intensity along a scanline by two additions per pixel. The methods presented are generally applicable and can easily be implemented in hardware.

Incremental Polygon Rendering on a SIMD Processor Array

AbstractWe demonstrate how both area coherence and parallelism can be exploited in order to speed up rendering operations on a SIMD square array of processors. Our algorithms take advantage of the method of differences, in order to incrementally compute the values of a linear polynomial function at discrete intervals and thus implement area rendering operations efficiently. We discuss how filling of convex polygons, hidden surface elimination and smooth shading can be implemented on an N × N processor array that supports planar arithmetic, that is, arithmetic operations performed on N × N matrices in parallel for all matrix elements. A major attraction of the method we present is that it is based on a SIMD processor array; such machines are now recognised as highly general purpose given the wide range of applications successfully implemented on them.

Spherical harmonic molecular surfaces

Starlike surfaces can be defined in spherical coordinates by a function r( theta , phi ) on the unit sphere, which can be expanded in spherical harmonics to give a consequence of smooth approximations to the surface. This method has been used to approximate the solvent-accessible surface of a molecule. The coefficients in the expansion provide a small collection of numbers that characterize the molecular shape. The resulting smooth surfaces can be rendered with random dots or smooth shading. These spherical harmonic surfaces have advantages for modeling overall molecular shape, particularly time-averaged shapes relevant to electrostatic and other intermolecular interactions. >