Some improvements exploit the high coherency between the pixels in image space, or between the voxels in object space. The secret of popularity of the ray casting technique is, beyond its simplicity and easy programmability on both CPUРІР‚в„ўs and GPUРІР‚в„ўs, that it can be optimized in several ways. The basic idea behind it is casting a ray into the volume from each pixel of the screen, sampling the volume along the ray in a front-to-back or back-to-front order and finally compositing the optical values at the sampling points, thus obtaining the final color of the pixel. Ray casting, similarly to the other above-mentioned techniques, is a Direct Volume Rendering method (DVR) as it displays the 3D dataset without computing any intermediate geometry representations. A good example of this evolution is the recent version of Visualization Toolkit, in which GPU ray casting is applied as the default volume rendering algorithm, and if it is not supported by the hardware, 3D texture mapping is chosen for interactive and CPU ray casting for still rendering. The winners of this change have been the ray casting and 3D texture mapping, methods, the most popular ones to date, while some other previously dominant techniques, like the splatting and shear-warp algorithm, though attempts were made to port them onto GPUРІР‚в„ўs, have actually become extinct by today. provides insight into the latest Augmented Reality (AR) and Virtual Reality (VR) technologies to display medical images.Р”Р„t first volume rendering algorithms were executed by the Central Processing Unit (CPU), and after the appearance of generally programmable Graphics Processing Units GPUРІР‚в„ўs they became run as shader programs on the graphics hardver. , while Zhang and his colleagues give us a comprehensive summary of the topic, mostly focusing on medical applications. A rather old but still relevant list of the most popular methods can be found in the study of MeiР“Сџner et al. In the last three decades several techniques have been developed for displaying volumetric datasets.

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