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Visualization of Bioelectric Phenomena
Published in Theo C. Pilkington, Bruce Loftis, Joe F. Thompson, Savio L-Y. Woo, Thomas C. Palmer, Thomas F. Budinger, High-Performance Computing in Biomedical Research, 2020
Thomas C. Palmer, Edward V. Simpson, Katherine M. Kavanagh, William M. Smith
An important distinction between volume Tenderers is the order in which voxels are processed to create an image. Image-order algorithms scan the image plane and, for each pixel, determine which voxels contribute to the final color. This approach, also known as ray tracing, casts one or more rays per pixel from the viewpoint into the volume. At evenly spaced intervals along each ray, samples are calculated via trilinear interpolation of the eight voxels in the current cell. Opacity and color are accumulated until either the opacity reaches one (opaque) or the ray exits the volume.1–3 Recursive ray tracing, where reflection, refraction, and shadowing rays are spawned from each ray–volume intersection, is rarely attempted due to the huge computational cost involved. Object-order methods scan the volume and determine which pixels a given voxel can effect. These methods avoid the linear interpolation typically used in ray tracing by directly projecting voxels onto the image plane.3–5
A Systematic Review of 3D Imaging in Biomedical Applications
Published in K.C. Santosh, Sameer Antani, D.S. Guru, Nilanjan Dey, Medical Imaging, 2019
Darshan D. Ruikar, Dattatray D. Sawat, K.C. Santosh
A hybrid DVR algorithm shear-warp is one of the fastest volume rendering algorithms. It attempts to combine the advantages of both the image order-based and object order-based volume rendering methods. It uses run-length encoding (RLE) compression to compress volume the data, which allows fast streaming through it. In addition to this, it factorizes the viewing transformation into 3D shear and warp transformation in the 2D plane [8,9]. Figure 8.5 shows the transformation of shared object space from the parallel projection tothe original object space. The shear-warp algorithm achieves greater rendering speed at the cost of image quality. To overcome this drawback, i.e. to maintain image quality while rendering the pre-integrated volume, rendering in the shear-warp algorithm for parallel projection is implemented in Schulze et al. [21]. Further, Kye et al. [22] presented two methods to improve image quality. In the first method, super-sampling is performed in an intermediate image space, whereas the second method uses a pre-integrated rendering technique with the help of a new data structure named “overlapped min-max block.”
Advanced Applications of Volume Visualization Methods in Medicine
Published in Alexander D. Poularikas, Stergios Stergiopoulos, Advanced Signal Processing, 2017
Georgios Sakas, Grigorios Karangelis, Andreas Pommert
In volume-based rendering, we basically have the choice between two scanning strategies: pixel by pixel (image order) or voxel by voxel (volume order). These strategies correspond to the image and object order rasterization algorithms used in computer graphics.32 In image order scanning, the data volume is sampled on rays along the view direction. This method is commonly known as ray casting:47FOR each pixel on image plane DO FOR each sampling point on associated viewing ray DO compute contribution to pixel The principle is illustrated in Figure 4.6. Along the ray, visibility of surfaces and objects is easily determined. The ray can stop when it meets an opaque surface. Yagel et al. extended this approach to a full ray tracing system which follows the viewing rays as they are reflected on various surfaces.125 Multiple light reflections between specular objects can thus be handled.
i4Ocean: transfer function-based interactive visualization of ocean temperature and salinity volume data
Published in International Journal of Digital Earth, 2021
Fenglin Tian, Qing Mao, Yazhen Zhang, Ge Chen
Over time, many techniques have been developed to render volumetric data, and some of the most common methods include surface rendering and DVR. DVR directly generates 2D images from 3D volumetric data by projections of a volume without generating any intermediate geometric primitive representation (Johnson and Hansen 2005). DVR can present the overall information and internal structure of volume-containing mixtures of materials simultaneously, and an optical integral model (Max 1995) is used to directly evaluate the contributions of actual data samples to the 2D image (Drebin, Carpenter, and Hanrahan 1988). Moreover, the ray casting algorithm is the most commonly used algorithm in DVR. The first ray casting algorithm based on GPU was introduced by Krüger and Westermann (2003), and it integrated early ray termination and empty-space skipping (Levoy 1990; Danskin and Hanrahan 1992; Yagel and Shi 1993; Freund and Sloan 1997) into texture-based volume rendering to decrease per-fragment operations. There has been a growing body of research on the application of DVR in various fields. Li and Zhang (2010) developed an efficient volume rendering system based on ray casting to highlight different organs/tissues in a CT volume. Marco, Tobias, and Carsten (2015) presented a novel method to optimize the attenuation of light for a single scattering model in DVR. An algorithm was presented by Binyahib et al. (2019) for parallel volume rendering that was a hybrid between the classical object order and the image order.