Barthold Lichtenbelt

Frequency analysis of gradient estimators in volume rendering

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.

Design of a high performance volume visualization system

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. CR

Improving image quality of volume-rendered three-dimensional medical data

Volume visualization is the technique of displaying two dimensional projections of three dimensional data. The data is acquired from a medical scanner, like MRI, CT, SPECT, or US scanners. Visualizing a given three dimensional medical dataset can be done by surface rendering algorithms or by direct volume rendering algorithms. Surface rendering algorithms require an intermediate geometric representation and are therefore less attractive. In our approach volume rendering is used. To improve image quality of such projections of the volume data, special care should be taken to (a) the interpolation step, (b) the estimation of the local gradient and (c) the assignment of opacity values at sample positions. These aspects are addressed in this paper.

An architecture for high-performance 2-D image display

Image processing operations can be divided into two classes, those pre-processing operations that are market- and application-specific, and those widely-used operations that are useful in any application that requires the display of two-dimensional images. In the interest of achieving real-time rates for the broader class of 2-D image display operations, Hewlett-Packard has developed a hardware accelerator called VISUALIZE-IVX. It is capable of scaling, rotating, mirroring, translating and filtering lk-by-lk output images at greater than 30 frames/sec while simultaneously enhancing image brightness and contrast. This paper describes the pipelined architecture used to achieve this performance oh a desktop computer. The Architecture makes use of a hybrid mapping scheme for geometric transformations. Also a unique memory device was designed that minimizes local image buffers while eliminating the need to resend pixels from main memory. A recently developed method of extending the filtering capabilities, that may be incorporated into future products, is also presented.