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Rational Filters for Passive Depth from Defocus
 International Journal of Computer Vision
, 1998
"... A fundamental problem in depth from defocus is the measurement of relative defocus between images. The performance of previously proposed focus operators are inevitably sensitive to the frequency spectra of local scene textures. As a result, focus operators such as the Laplacian of Gaussian result i ..."
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Cited by 49 (3 self)
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A fundamental problem in depth from defocus is the measurement of relative defocus between images. The performance of previously proposed focus operators are inevitably sensitive to the frequency spectra of local scene textures. As a result, focus operators such as the Laplacian of Gaussian result in poor depth estimates. An alternative is to use large filter banks that densely sample the frequency space. Though this approach can result in better depth accuracy, it sacrifices the computational efficiency that depth from defocus offers over stereo and structure from motion. We propose a class of broadband operators that, when used together, provide invariance to scene texture and produce accurate and dense depth maps. Since the operators are broadband, a small number of them are sufficient for depth estimation of scenes with complex textural properties. In addition, a depth confidence measure is derived that can be computed from the outputs of the operators. This confidence measure perm...
A Rendering Algorithm for Discrete Volume Density Objects
, 1993
"... : We present a new algorithm for simulating the effect of light travelling through volume objects. Such objects (haze, fog, clouds...) are usually modelized by voxel grids which define their density distribution in a discrete tridimensional space. The method we propose is a twopass MonteCarlo ray ..."
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Cited by 48 (1 self)
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: We present a new algorithm for simulating the effect of light travelling through volume objects. Such objects (haze, fog, clouds...) are usually modelized by voxel grids which define their density distribution in a discrete tridimensional space. The method we propose is a twopass MonteCarlo raytracing algorithm that does not make any restrictive assumptions neither about the characteristics of the objects (both arbitrary density distributions and phase functions are allowed) nor about the physical phenomena included in the rendering process (multiple scattering is accounted for). The driving idea of the algorithm is to use the phase function for MonteCarlo sampling, in order to modify the direction of the ray during scattering. Keywords : MonteCarlo RayTracing, Participating Media, Volume Density Objects, Multiple Scattering. 1 Introduction Rendering methods of objects defined by their density distribution in a tridimensional space can be divided in viewdependent and viewi...
Image Coding By Block Prediction Of Multiresolution Subimages
 IEEE Transactions on Image Processing
"... The redundancy of the multiresolution representation has been clearly demonstrated in the case of fractal images, but it has not been fully recognized and exploited for general images. Recently, fractal block coders have exploited the selfsimilarity among blocks in images. In this work we devise ..."
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Cited by 33 (2 self)
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The redundancy of the multiresolution representation has been clearly demonstrated in the case of fractal images, but it has not been fully recognized and exploited for general images. Recently, fractal block coders have exploited the selfsimilarity among blocks in images. In this work we devise an image coder in which the causal similarity among blocks of different subbands in a multiresolution decomposition of the image is exploited. In a pyramid subband decomposition, the image is decomposed into a set of subbands which are localized in scale, orientation and space. The proposed coding scheme consists of predicting blocks in one subimage from blocks in lower resolution subbands with the same orientation. Although our prediction maps are of the same kind of those used in fractal block coders, which are based on an iterative mapping scheme, our coding technique does not impose any contractivity constraint on the block maps. This makes the decoding procedure very simple and...
Fractal Approaches for Visualizing Huge Hierarchies
 In Proceedings of the 1993 IEEE Symposium on Visual Languages
, 1993
"... This paper describes fractal approaches to the problems which associate with visualizing huge hierarchies. The geometrical characteristic of a fractal, selfsimilarity, allows users to visually interact with a huge tree in the same manner at every level of the tree. The fractal dimension, a measure o ..."
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Cited by 23 (1 self)
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This paper describes fractal approaches to the problems which associate with visualizing huge hierarchies. The geometrical characteristic of a fractal, selfsimilarity, allows users to visually interact with a huge tree in the same manner at every level of the tree. The fractal dimension, a measure of complexity, makes it possible to control the total amount of displayed nodes. A prototype visualization system for UNIX directories is also shown. 1 Introduction Visualization systems for hierarchical structures, especially for huge 1 data structures, have a potential usefulness. For example, the visualization of whole UNIX directories might help system administrators to maintain the file systems. Since administrators could recognize, through the visualization, local file systems of each computer and remote file systems mounted by using NFS (Network File System), they might avoid mistakes, such as deleting or moving files which are being referenced by other computers. It is, however, m...
TwoDimensional Simulation of Gaseous Phenomena Using Vortex Particles
 In Proceedings of the 6th Eurographics Workshop on Computer Animation and Simulation
, 1995
"... This article presents a simple, fast and stable method for the animation and visualisation of turbulent gaseous fluids in two dimensions. We draw on well known methods from computational fluid dynamics to model the fluid using vorticity and velocity fields. While the vorticity is transported by a ..."
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Cited by 23 (1 self)
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This article presents a simple, fast and stable method for the animation and visualisation of turbulent gaseous fluids in two dimensions. We draw on well known methods from computational fluid dynamics to model the fluid using vorticity and velocity fields. While the vorticity is transported by a particle system, we use a uniform grid to compute velocities and displacements for each particle. This mixed approach where free particles move on a fixed grid requires little computational power, making it suitable for computer animation. The method simulates the behaviour of fluids in situations where the contact between fluid masses with different velocities generates an intermediate mixing layer which can give rise to turbulence phenomena. Unlike previous algorithms, it is possible to generate quasiturbulent patterns, where large scale coherent vortex structures are still discernible in the flow.
Hierarchical Interpretation of Fractal Image Coding and Its Application to Fast Decoding
 in Proc. Digital Signal Processing Conference
, 1993
"... The basics of a block oriented fractal image coder, are described. The output of the coder is an IFS (Iterated Function System) code, which describes the image as a fixedpoint of a contractive transformation. A new hierarchical interpretation of the IFS code, which relates different scales of the f ..."
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Cited by 19 (4 self)
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The basics of a block oriented fractal image coder, are described. The output of the coder is an IFS (Iterated Function System) code, which describes the image as a fixedpoint of a contractive transformation. A new hierarchical interpretation of the IFS code, which relates different scales of the fixedpoint to the code, is presented and proved. The proof is based on finding a function of a continuous variable, from which different scales of the signal can be derived. Its application to a fast decoding algorithm is then described, leading typically to an order of magnitude reduction of computation time. I Introduction The use of fractal shapes to describe real world scenes has been shown to result in very realistic images [1]. This is due to the selfsimilarity property of fractal shapes, a property which is frequently encountered in real world scenes [2]. One way of creating a fractal shape is by considering it as a fixedpoint of a contractive Iterated Function System (IFS) [3]. Th...
A Fractal Model of Mountains with Rivers
 IN PROCEEDINGS OF GRAPHICS INTERFACE '93
, 1993
"... This paper addresses the longstanding problem of generating fractal mountains with rivers, and presents a partial solution that incorporates a squigcurve model of a river's course into the midpointdisplacement model for mountains. The method is based on the observation that both models can be exp ..."
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Cited by 18 (0 self)
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This paper addresses the longstanding problem of generating fractal mountains with rivers, and presents a partial solution that incorporates a squigcurve model of a river's course into the midpointdisplacement model for mountains. The method is based on the observation that both models can be expressed by similar contextsensitive rewriting mechanisms. As a result, a mountain landscape with a river can be generated using a single integrated process.
An Importance Driven MonteCarlo Solution to the Global Illumination Problem
, 1994
"... : We propose a method for solving the global illumination problem with no restrictive assumptions concerning the behaviour of light either on surface or volume objects in the scene. Surface objects are defined either by facets or parametric patches and volume objets are defined by voxel grids which ..."
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Cited by 17 (0 self)
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: We propose a method for solving the global illumination problem with no restrictive assumptions concerning the behaviour of light either on surface or volume objects in the scene. Surface objects are defined either by facets or parametric patches and volume objets are defined by voxel grids which define arbitrary density distributions in a discrete tridimensional space. The rendering technique is a MonteCarlo raytracing based radiosity which unifies the processing of objects in a scene, whether they are surfacic or volumic. The main characteristics of our technique are the use of separated Markov chains to prevent the explosion of the number of rays and an optimal importance sampling to speedup the convergence. Keywords : Global Illumination, MonteCarlo RayTracing, Importance Sampling, Participating Media. 1 Introduction Solving the global illumination problem is necessary to achieve photorealism in image synthesis [7, 16, 14]. To account for all complex reflection/transmission...
tracing deterministic 3D fractals
 Computer Graphics
, 1989
"... As shown in 1982, Julia sets of quadratic functions as well as many other deterministic fractals exist in spaces of higher dimensionality than the complex plane. Originally a boundarytracking algorithm was used to view these structures but required a large amount of storage space to operate. By ray ..."
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Cited by 16 (6 self)
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As shown in 1982, Julia sets of quadratic functions as well as many other deterministic fractals exist in spaces of higher dimensionality than the complex plane. Originally a boundarytracking algorithm was used to view these structures but required a large amount of storage space to operate. By ray tracing these objects, the storage facilities of a graphics workstation frame buffer are sufficient. A short discussion of a specific set of 3D deterministic fractals precedes a full description of a raytracing algorithm applied to these objects. A comparison with the boundarytracking method and applications to other 3D deterministic fractals are also included. CR Categories and Subject Descriptors: