Chroma-depth volume contribution shader used with 3 different color transfer function produces.

<p>(a)Chroma-depth, (b)Pseudo chroma-depth and (c)Aerial perspective.</p

Decluttering an angiographic CT to highlight the structure of interest, an AVM.

<p>(a) The original CTA volume rendered with Blinn-Phong shading. (b) A volume containing the topological distance to the AVM for each voxel. (c) The decluttered image obtained by combining (a) and (b).</p

Illustration of volume carving and opacity peeling methods.

<p>(a) Original MRI volume, (b) Volume Carving with a spherical tool, (c) Opacity peeling where the first layer is peeled off.</p

Edge enhancement of an angiographic CT.

<p>The volume is rendered with (a) only the edge rendering shader, (b) Only a Blinn-Phong shader, (c) Edge and Blinn-Phong shader combined.</p

Comparison of the frame rates obtained with the VTK GPU raycast volume renderer and the PRISM framework with and without the early ray termination (ETR) optimization with an alpha threshold of 0.99.

<p>Comparison of the frame rates obtained with the VTK GPU raycast volume renderer and the PRISM framework with and without the early ray termination (ETR) optimization with an alpha threshold of 0.99.</p

Frame rate in frames per second (fps) for the different volume rendering examples presented in this paper.

<p>Note that pseudo chroma-depth and aerial perspective are not listed as they differ from chroma-depth only in the content of the transfer function and not in the computation. In practice the frame rate difference was not measurable.</p

A 320x320x280 voxel volume rendered using the default modes.

<p>a) the VTK GPU raycast volume renderer, b) the flexible PRISM GPU raycast framework and c) the PRISM framework with early ray termination (ERT).</p

Illustration of the emission-absorption model used to compute the color of a pixel.

<p>A ray is cast from the virtual camera through the pixel in the image plane. The intersection with the volume is found and the volume is sampled at regular interval, the sample value is mapped to optical properties which are composited to obtain the pixel color.</p

Blood flow depiction.

<p>(a) The original CTA volume rendered with Blinn-Phong shading. (b) Volume containing precomputed blood flow information, i.e. distance, within vessels, between entry and exit of blood from the brain. (c) Volume from (b) combined with (a) using the Volume shader of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193636#pone.0193636.box006" target="_blank">Algorithm 6</a>. When the time parameter is updated to render each frame, the waves move along the vessels in the direction of the blood flow as illustrated in the accompanying video (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193636#pone.0193636.s004" target="_blank">S1 Video</a>).</p

Mean and standard deviation of the answers provided by the users on the online questionnaire.

<p>Each question is answered on a scale of 1 to 5 (1 = strongly disagree, 5 = strongly agree). The System Usability Scale (SUS) score (last line of part 2) is obtained by subtracting 1 from the score of each odd-numbered question and subtracting the score of even-numbered from 5. We sum the results obtained for each question and multiply by 2.5 to obtain the final score.</p