Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master 's thesis, Cornell University, January 1992.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....a polynomial integrated over regions of the sphere. Spatially varying luminaires constitute an important class of light sources with immediate applications to higher order finite element methods for global illumination, both for direct lighting [9] and final gathers from coarse global solutions [13]. Few methods exist for handling this type of luminaire aside from Monte Carlo integration. DiLaura [8] and the authors [6] have addressed the problem of computing the irradiance at a point from spatially varying luminaires with polynomially varying radiant exitance. Both employed Stokes theorem ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master 's thesis, Cornell University, January 1992.

....with the future direction of research are presented in section 7. 2 Previous work 2. 1 View Dependent Radiosity Methods Although most radiosity methods are inherently view independent, some techniques incorporate view dependent information at different radiosity processing stages: Two Pass [14, 13, 9], Multi Pass methods [2] and Importance based radiosity. Since this paper is restricted to diffuse interreflections, the two former ones will not be addressed here. Importance based radiosity [17] aims at computing as exactly as possible the radiosities of the elements that will have a ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Program of Computer Graphics, Cornell University, January 1992.

....hierarchical radiosity. However, these previous works deal with the global solution of the system. For high quality rendering, this global solution is not su#cient unless una#ordable refinement levels of the solution are reached. On the contrary, high quality images require a final gathering step [16]. Di#erent two pass strategies have been developed in the literature [17, 18, 19, 20, 21] but none of them has been adapted to a dynamic environment. Analyzing the cost of the two steps, it is clear that the local pass cost is considerably higher than the global one: from twice to ten times more ....

....an interval of time. 18 Figure 5 shows an example of how the global solution and the texture movie hierarchy is incrementally updated following the criteria exposed above. The figure represents a 17 frames interval with two patches P 1 and P 2 that are visible in the sub intervals [0, 9] and [7, 16] respectively. There are 5 main steps in the computation of the sequence: 1. Frame 0 is requested and the first action is to compute the interval extent for the patches until the extent of all visible patches in frame 0 has been fully computed. Only P 1 is visible at frame 0 so the extent ....

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M. C. Reichert, "A Two-Pass Radiosity Method Driven by Lights and Viewer Position," m.Sc. thesis, Ithaca, NY, January 1992.

....is a piecewise constant approximation to the radiance function, such a rendering would produce a blocky image. Furthermore, we want a rendering algorithm that would produce images of high visual quality even from very coarse finite element solutions. Thus, following the ideas that Reichert [26], Lischinski et al. 21] and Smits [33] used for radiosity, we use a final gather step. In this step, the image is rendered by casting rays from the eye through the pixels. At each visible point in the scene we compute the radiance outgoing towards the eye by gathering radiance one last time ....

M. C. Reichert. A Two-Pass Radiosity Method Driven by Lights and Viewer Position, Master 's thesis, Program of Computer Graphics, Cornell University, Ithaca, New York, January 1992.

....resulting in visible discontinuities if the solution is displayed directly (e.g. CSSD96] Zatz [Zat93] used a Galerkin type method and shadow masks to improve the quality of the shadows generated. To avoid the problem of discontinuous representations the final gather step was introduced by [Rei92] and used for wavelet solutions (e.g. CSSD96] A final gather step consists of creating a ray cast image, by querying the object space visibility and lighting information to calculate illumination at each pixel. This approach allows the generation of high quality images from a coarse lighting ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Program of Computer Graphics, Cornell University, January 1992.

....value I(x; x 0 ) can be computed by the rendering equation. However, since this is a computer vision research, this computation is not needed. Indeed it is computed by Nature as the input image. This formulation is supported by the two pass rendering method in computer graphics research [11], in which the rendering equation is solved in the view independent first pass and the image viewed from a special direction is rendered by the second pass, where the solution of the first pass gives the interreflection which serves as the secondary illumination in the second pass. This ....

Reichert, M.C., A Two-Pass Radiosity Method Driven by Lights and Viewer Position, Master's Thesis, Program of Computer Graphics, Cornell University, January, 1992.

....[Computer Graphics ] Three Dimensional Graphics and Realism. Additional Key Words: clustering, error bounds, hierarchical radiosity, global illumination. 1 Introduction Recent trends in realistic image synthesis have been towards a separation of the rendering process into two or more stages[10, 2, 9]. One of these stages solves for the global energy equilibrium throughout the environment. This process can be very expensive and its complexity grows rapidly with the number of objects in the environment. These computational demands generally limit the level of detail of environments that can be ....

....to use the techniques of Lischinki et al. 9] and create a separate mesh for display purposes, using the information obtained by the global solution, and recomputing some parts of the illumination on each surface. Our approach is based on this method as well as on the method proposed by Reichert [10]. Given a view, we approximate the intensity 1000 10000 100000 1e 06 1e 07 100 1000 10000 100000 Link Cost Initial Surfaces s log s Trials Figure 5: Link cost for environments of different sizes compared with the function s log(s) by reconstructing the radiance function at each visible point in ....

REICHERT, M. C. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Program of Computer Graphics, Cornell University, Ithaca, New York, January 1992.

....on diffuse surfaces. This limits the utility of such methods for complex scenes. Rushmeier 1 observed that all lighting could be recomputed by gathering from a radiosity solution at each point[15] This method has been used to generate images using piecewise constant radiosity solutions[13, 20]. Lischinski et al. used a similar nonprobabilistic gather to generate better meshes for hardware display[11] More recently, Rushmeier et al. 14] observed that gathering from a piecewise constant radiosity solution could be done more efficiently if the radiosity solution were carried out for a ....

....background Where radiositycolor returns the color of the radiosity patch seen in the direction of the random ray (note that the emitted portion is not there) Figure 2b. 2. 4 Explicit Gather Alternatively, Equation 4 can be solved by sending a shadow ray to every patch in the radiosity solution[13], Figure 2c: color raycolor(ray) color L = 0; done = false if (ray hits at x) L = LE(x) for (i = 0 to numPatches) if (x t(xi x) hits at xi) L = LE(xi) R(x) L(xi) return L else return background where xi is a point in the radiosity solution. This method is very expensive for large ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Cornell Program of Computer Graphics, January 1992.

....on diffuse surfaces. This limits the utility of such methods for complex scenes. Rushmeier 1 observed that all lighting could be recomputed by gathering from a radiosity solution at each point[15] This method has been used to generate images using piecewise constant radiosity solutions[13, 20]. Lischinski et al. used a similar non probabilistic gather to generate better meshes for hardware display[11] More recently, Rushmeier et al. 14] observed that gathering from a piecewise constant radiosity solution could be done more efficiently if the radiosity solution were carried out for a ....

....background Where radiositycolor returns the color of the radiosity patch seen in the direction of the random ray (note that the emitted portion is not there) Figure 2b. 2. 4 Explicit Gather Alternatively, Equation 4 can be solved by sending a shadow ray to every patch in the radiosity solution[13], Figure 2c: color raycolor(ray) color L = 0; if (ray hits at x) L = LE(x) for (i = 1 to numPatches) if (x t(xi x) hits at xi) L = LE(xi) R(x) L(xi) return L else return background where xi is a point in the radiosity solution. This method is very expensive for large environments, but will ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master 's thesis, Cornell Program of Computer Graphics, January 1992.

....curved surfaces and anisotropic bidirectional reflectance distribution functions. The framework we describe naturally accommodates spatial variations, described by texture maps, in both emission and reflectance. Finally, to improve the visual quality of the image, a final gathering step is used [19]. 2 Finite Elements for Radiance In this section, we briefly review the equation that governs light transport, and describe how the finite element method can be used to compute approximate solutions. 2.1 Radiance Let x, y, and z be points in space. Radiance L(y z) is defined as the power ....

....of vanishing moments will increase the sparsity of the discrete approximation to that operator. P. Christensen, E. Stollnitz, D. Salesin and T. DeRose formulas. The main disadvantage of the Haar basis, its discontinuities, can be ameliorated by performing a final gathering step during rendering [19]. 3.3 A Four dimensional Wavelet Basis Four dimensional basis functions are required for representing radiance distributions: two variables describe spatial variation across a surface, and two variables describe angular variation. As is common, we split the surfaces into patches such that the ....

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Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Program of Computer Graphics, Cornell University, Ithaca, New York, January 1992.

....illumination is interpolated from the mesh. Kok et al. KJ92] describe a generalization of this approach in which illumination due to the most significant secondary reflectors as well as the emitters is recomputed during rendering, based on information gathered during the radiosity pass. Reichert [Reic92] calculates the local illumination for a point x by calculating the form factor and visibility to each element and summing up the contributions. This method is quite costly as all elements have to be processed for every pixel. H x A , B A ( 1 2p N G a a A FF x A , ....

M. C. Reichert, "A two-pass radiosity method driven by lights and viewer position ", Master's thesis, Program of Computer Graphics, Cornell University, Jan. 1992.

....aims of global illumination is the representation of surface radiance functions. The most popular approach used is a mesh of elements, typically utilising linear or constant basis functions to reconstruct illumination information [3] although higher order basis functions are also possible [2, 14] for non interactive viewing. Mesh based solutions to the global illumination problem rely heavily on the accuracy of the underlying mesh to model the radiance function across each surface. Each surface is typically given an initially coarse mesh which is then refined during the illumination ....

Mark C. Reichert. A Two-Pass Radiosity Method Driven by Lights and Viewer Position. M.Sc. thesis, Program of Computer Graphics, Cornell University, Ithaca, NY, January 1992.

....is a piecewise constant approximation to the radiance function, such a rendering would produce a blocky image. Furthermore, we want a rendering algorithm that would produce images of high visual quality even from very coarse finite element solutions. Thus, following the ideas that Reichert [26], Lischinski et al. 21] and Smits [34] used for radiosity, we use a final gather step. In this step, the image is rendered by casting rays from the eye through the pixels. At each visible point in the scene we compute the radiance outgoing towards the eye by gathering radiance one last time ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Cornell University, 1992.

....A complete solution to the global illumination problem should be both physically accurate and visually pleasing. However, many algorithms produce solutions that are numerically accurate yet still contain artifacts that are very obvious to the human eye. We therefore use a final gathering step [23, 28, 36] to improve the visual quality of the solution. We have implemented an algorithm based on the choices outlined above. Other features of the implementation include support for curved surfaces and anisotropic bidirectional reflectance distribution functions (BRDFs) Texture maps can be used to ....

....adaptively recomputed wherever the kernel is sampled densely. 5.5 Final gather In order to render the solution, we can either evaluate the finite element representation of the solution directly, or we can perform an extra step that improves its visual quality. Following the ideas that Reichert [28], Lischinski et al. 23] and Smits [36] used for radiosity, we have implemented a final radiance gathering step. For each pixel in the final image, we perform a final gathering of light to the surface point y that corresponds to the midpoint of the pixel. We have tried three different final ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Cornell University, 1992.

....of choice is in the rendering of the solution. A complete solution to the global illumination problem should be both physically accurate and visually pleasing. However, certain good approximations may have artifacts that are very obvious to the human eye. We therefore use a final gathering step [25, 30, 36] to improve the visual quality of the solution. We have implemented an algorithm based on these choices. Adaptive numerical integration is used to compute accurate light transports where needed. The implementation also supports curved surfaces and spatially varying anisotropic bidirectional ....

....topology (for example, the floor in Figure 21) Both approaches seem unnecessarily complicated compared to the alternative, a discontinuous basis. Discontinuous wavelet bases that have been used for radiosity include the Haar basis, multiwavelets, and flatlets [20] A final gathering step [25, 30, 36] can be used to smooth out discontinuities in the basis and at patch boundaries. We have experimented with bounded interval B spline wavelets [7] Daubechies wavelets, and the Haar basis. As a result of these experiments, we have chosen to implement our glossy global illumination algorithm using ....

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Mark C. Reichert. A Two-Pass Radiosity Method Driven by Lights and Viewer Position. Master's thesis, Program of Computer Graphics, Cornell University, Ithaca, New York, January 1992.

.... = L e (x) f r (x) X j Z A j L(y)G(x; y)dA y : All terms Z A j L(y)G(x; y)dA y = L j Z A j G(x; y)dA y = L j F dAx ;j ; where F dAx ;j is the point x to patch j form factor, are evaluated with equal precision regardless of the contribution of element j to the illumination at x [8]. When the point to patch form factors are computed by integration over the surface of the patches j, some artifacts may occur near discontinuities in the radiosity kernel G(x; y) These can be remedied by evaluating the pointto patch form factors using integration over the spherical triangle or ....

Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master 's thesis, Program of Computer Graphics, Cornell University, January 1992.

....is a piecewise constant approximation to the radiance function, such a rendering would produce a blocky image. Furthermore, we want a rendering algorithm that would produce images of high visual quality even from very coarse finite element solutions. Thus, following the ideas that Reichert [26], Lischinski et al. 21] and Smits [33] used for radiosity, we have implemented a final gather step. In this step, the image is rendered by casting rays from the eye through the pixels. At each visible point in the scene we compute the radiance outgoing towards the eye by gathering radiance one ....

M. C. Reichert. A Two-Pass Radiosity Method Driven by Lights and Viewer Position, Master's thesis, Program of Computer Graphics, Cornell University, Ithaca, New York, January 1992.

....to the radiance function. Thus, results of high visual quality can beobtained even from coarse global illumination simulations. Previous attempts to improve the visual quality of radiosity solutions were described by Nishita and Nakamae [19] Kok and Jansen [17] Chen et al. 4] and Reichert [20]. In all of these cases, however, the improvement takes place in image space, after the view and the resolution have been specified. Our method, instead, operates entirely in object space, and the improved solution is view independent. 2 HIERARCHICAL RADIOSITY The traditional radiosity approach ....

Reichert, Mark C. A Two-Pass Radiosity Method Driven by Lights and Viewer Position, Master's thesis, Cornell University, Ithaca, New York, January 1992.

....value of the element visible through the pixel. However, the finite element solution typically looks blocky and is not refined far enough to show texture. An alternative approach is to perform a rendering step that improves the visual quality of the solution. Following the ideas that Reichert [25], Lischinski et al. 22] and Smits [31] used for radiosity, we have implemented a final radiance gathering step. The image is rendered by casting rays from the eye. At each visible point in the scene we compute the radiance reflected towards the eye by transporting radiance one last time through ....

M. C. Reichert. A Two-Pass Radiosity Method Driven by Lights and Viewer Position, Master's thesis, Program of Computer Graphics, Cornell University, Ithaca, New York, January 1992.

....curved surfaces and anisotropic bidirectional reflectance distribution functions. The framework we describe naturally accommodates spatial variations, described by texture maps, in both emission and reflectance. Finally, to improve the visual quality of the image, a final gathering step is used [18]. y Per H. Christensen, Eric J. Stollnitz, David H. Salesin, and Tony D. DeRose. Wavelet radiance. In G. Sakas, P. Shirley, and S. Muller, editors, Photorealistic Rendering Techniques, pages 295 309. Springer Verlag, Berlin, 1995. Reprinted from Proceedings of the Fifth Eurographics Workshop on ....

....support, requiring costly quadrature formulas. Multiwavelets [13] are constructed from higher order polynomials, which also require costly quadrature formulas. The main disadvantage of the Haar basis, its discontinuities, can be ameliorated by performing a final gathering step during rendering [18]. 3.3 A Four Dimensional Wavelet Basis Four dimensional basis functions are required for representing radiance distributions: two variables describe spatial variation across a surface, and two variables describe angular variation. As is common, we split the surfaces into patches such that the ....

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Mark C. Reichert. A two-pass radiosity method driven by lights and viewer position. Master's thesis, Cornell University, 1992.

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M. C. Reichert, "A Two-Pass Radiosity Method Driven by Lights and Viewer Position", m.Sc. thesis, Ithaca, NY, (January 1992).

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