## Opacity-Weighted Color Interpolation For Volume Sampling (1998)

Venue: | IEEE Symposium on Volume Visualization |

Citations: | 42 - 3 self |

### BibTeX

@INPROCEEDINGS{Wittenbrink98opacity-weightedcolor,

author = {Craig M. Wittenbrink and Tom Malzbender and Michael E. Goss},

title = {Opacity-Weighted Color Interpolation For Volume Sampling},

booktitle = {IEEE Symposium on Volume Visualization},

year = {1998},

pages = {135--142}

}

### Years of Citing Articles

### OpenURL

### Abstract

volume rendering, compositing, ray tracing Volume rendering creates images from sampled volumetric data. The compute intensive nature of volume rendering has driven research in algorithm optimization. An important speed optimization is the use of preclassification and preshading. We demonstrate an artifact that results when interpolating from preclassified or preshaded colors and opacity values separately. This method is flawed, leading to visible artifacts. We present an improved technique, opacity-weighted color interpolation, evaluate the RMS error improvement, hardware and algorithm efficiency, and demonstrated improvements. We show analytically that opacity-weighted color interpolation exactly reproduces material based interpolation results for certain volume classifiers, with the efficiencies of preclassification. Our proposed technique may also have broad impact on opacitytexture-mapped polygon rendering.

### Citations

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Citation Context ...]. Kajiya provided a generalization to nonhomogeneous volumetric media, and developed single and multiscattering solutions [KH84]. Modern direct volume rendering algorithms are largely based on Levoy =-=[Lev88]-=-, Drebin et al. [DCH88], Sabella [Sab88], and Upson et al. [UK88]. (Note: the work in [DCH88] was demonstrated a couple of years prior to publication, but not released due to its proprietary nature to... |

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Citation Context .... But, opacity-weighted color interpolation is an unpublished technique as demonstrated here except for Drebin et al. [DCH88] who preweight entire volumes. Examination of source code has shown others =-=[LL94]-=- have used similar solutions. Drebin et al. [DCH88] specify opacity weighting of the colors for volume rendering by preweighting. Others have noted the difficulties associated with opacity and color, ... |

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Citation Context ... the context of ray cast volume rendering in this paper. However, the suitability of the interpolation method presented is not limited to ray-casting and applies to other techniques such as splatting =-=[Wes90]-=-, threedimensional texture mapping [VGK96], and polygon rendering as well. There are three alternative approaches to avoiding the interpolation artifacts described in Section 2. These are summarized i... |

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Citation Context ... technique may also have broad impact on opacity-texture-mapped polygon rendering. Keywords: volume rendering, compositing, ray tracing. 1 INTRODUCTION Volume rendering as introduced by Drebin et al. =-=[DCH88]-=- demonstrated classification and shading. Other research has focused on approximation algorithms for speed and parallelization approaches for throughput. There remain subtleties in the proper developm... |

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Citation Context ...e lighting of layers of homogeneous particles, to render Saturn’s rings. The common algebraic technique for combining ray samples isscompositing, derived separately by Blinn [Bli82] and Porter et al. =-=[PD84]-=-. Kajiya provided a generalization to nonhomogeneous volumetric media, and developed single and multiscattering solutions [KH84]. Modern direct volume rendering algorithms are largely based on Levoy [... |

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Citation Context ... the work in [DCH88] was demonstrated a couple of years prior to publication, but not released due to its proprietary nature to Pixar). Max has published a survey of direct volume solution approaches =-=[Max95]-=-. Nonparticle model volumetric approaches were widely developed before 1988, including [Mea82,Mea85,Kau91]. Other related work in particle and radiative transfer theory applied to volume visualization... |

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Citation Context ...e based on the physics of light interaction with modeled particles in a volume. The beginnings of a particle model for graphics rendering were developed by Blinn [Bli82] and extended by Kajiya et al. =-=[KH84]-=- to nonhomogeneous densities of particles. Blinn adapted the radiative transfer theory particle model for realistic image synthesis [Bli82] from Esposito [Esp79] Chandresakar [Cha60] and others. Blinn... |

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Citation Context ...el volumetric approaches were widely developed before 1988, including [Mea82,Mea85,Kau91]. Other related work in particle and radiative transfer theory applied to volume visualization includes [Max86]=-=[KK89]-=-. As direct solution of the posed integro-differential equations for the radiative transfer of light through a nonhomogeneous model is not in general analytically solvable [KH84][Max95], and numerical... |

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Citation Context ...l Model Volume rendering algorithms are based on the physics of light interaction with modeled particles in a volume. The beginnings of a particle model for graphics rendering were developed by Blinn =-=[Bli82]-=- and extended by Kajiya et al. [KH84] to nonhomogeneous densities of particles. Blinn adapted the radiative transfer theory particle model for realistic image synthesis [Bli82] from Esposito [Esp79] C... |

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Citation Context ...onhomogeneous volumetric media, and developed single and multiscattering solutions [KH84]. Modern direct volume rendering algorithms are largely based on Levoy [Lev88], Drebin et al. [DCH88], Sabella =-=[Sab88]-=-, and Upson et al. [UK88]. (Note: the work in [DCH88] was demonstrated a couple of years prior to publication, but not released due to its proprietary nature to Pixar). Max has published a survey of d... |

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Citation Context ...edia, and developed single and multiscattering solutions [KH84]. Modern direct volume rendering algorithms are largely based on Levoy [Lev88], Drebin et al. [DCH88], Sabella [Sab88], and Upson et al. =-=[UK88]-=-. (Note: the work in [DCH88] was demonstrated a couple of years prior to publication, but not released due to its proprietary nature to Pixar). Max has published a survey of direct volume solution app... |

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Citation Context ...ebin et al. [DCH88] specify opacity weighting of the colors for volume rendering by preweighting. Others have noted the difficulties associated with opacity and color, notably Wilhelms and Van Gelder =-=[WVG91]-=- and Blinn [Bli94], but not as it relates to resampling of shaded color values in volume ray tracing. Wilhelms notes that different answers will result if one interpolates colors versus data, but the ... |

30 |
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Citation Context ...cle model volumetric approaches were widely developed before 1988, including [Mea82,Mea85,Kau91]. Other related work in particle and radiative transfer theory applied to volume visualization includes =-=[Max86]-=-[KK89]. As direct solution of the posed integro-differential equations for the radiative transfer of light through a nonhomogeneous model is not in general analytically solvable [KH84][Max95], and num... |

21 |
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Citation Context ...in this paper. However, the suitability of the interpolation method presented is not limited to ray-casting and applies to other techniques such as splatting [Wes90], threedimensional texture mapping =-=[VGK96]-=-, and polygon rendering as well. There are three alternative approaches to avoiding the interpolation artifacts described in Section 2. These are summarized in Table 2. The first alternative is to sto... |

7 | Decisions in Volume Rendering - Wilhelms - 1991 |

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(Show Context)
Citation Context ...ATE INTERPOLATION OF COLOR AND OPACITY Using the approach shown in Figure 1, the optical model basis just discussed, EQ (3), let us examine in detail how to perform the calculation. We follow Blinn’s =-=[Bli94]-=- notation for an opacityweighted color, which he calls an associated color, and denotes it as ~ C = αC where C is simply the nonweighted color, or gray level. The compositing equations are [Bli94] (fo... |

2 |
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(Show Context)
Citation Context ...d by Kajiya et al. [KH84] to nonhomogeneous densities of particles. Blinn adapted the radiative transfer theory particle model for realistic image synthesis [Bli82] from Esposito [Esp79] Chandresakar =-=[Cha60]-=- and others. Blinn’s analytical solutions solved the lighting of layers of homogeneous particles, to render Saturn’s rings. The common algebraic technique for combining ray samples isscompositing, der... |

1 | et al., “A ‘virtual body’ model for surgical education and rehearsal - Hohne - 1996 |