Abstract-Gradient information is used in volume rendering to classify and color samples along a ray. In this paper, we present an analysis of the theoretically ideal gradient estimator and compare it to some commonly used gradient estimators. A new method is presented to calculate the gradient at arbitrary sample positions, using the derivative of the interpolation filter as the basis for the new gradient filter. As an example, we will discuss the use of the derivative of the cubic spline. Comparisons with several other methods are demonstrated. Computational efficiency can be realized since parts of the interpolation computation can be leveraged in the gradient estimation.
Visunlizing three dimensional discrete datasets has been a topic of many research projects and papers in the past decade. We discuss the issues that come up when designing a whole computer system cnpable of visualizing these datasets in real time. We explain the three way chicken and egg problem and discuss HewlettPackard's effort at breaking it with the Voxelator API extensions to OpenGL. We enumerate what a good hardware design should accomplish, We discuss what system issues are important and show how to integrate volume visualization hardware in one of Hewlett-Packard's graphics accelerators, the VISUALIZE-48XP. We show why the Voxelator is an efficient and well designed API by explnining how various existing hardware engines will easily tit into the Voxelator framework.
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