VolVis

What is it ?	This Program is designed for viewing computer tomography volume data interactively. The volume data is rendered by a direct volume rendering algorithm, which is explained briefly in the section "The Algorithm" below.
Features	Supported file formats: Raw volume data files and Hewlett-Packard volume data files Orthogonal Projection Interactive Transparency Control Interactive Threshold Control Interactive Rotating - Fast Preview using OpenGL Surface Rendering Maximum Intensity Rendering New in Version 1.1: Surface Rendering with Shear Warp
The Algorithm	Raycasting: First the volume data is transformed into an orthogonal grid. After that the shading and the transparency information is generated from this data using user defined parameters mentioned above in the "Features" section. For every pixel drawn there is a ray casted into these data sets from front to the back. The accumulated value is used for the pixel color.
Requirements	Microsoft Windows 95/98/NT/2000/XP with OpenGL
Download	Download VolVis 1.0 with MSVC++ 6.0 Source Code - ZIP file, 158KB Download VolVis 1.1 with MSVC++ 6.0 Source Code - ZIP file, 106KB
Screenshot
Rendering Examples	Figure 1: Threshold Rendering: Nearest Neighbour vs. Trilinear Filtering Figure 2: Threshold Rendering: Trilinear Filtering and Highlighting with and without Transfer Function Figure 3: Transparency Rendering with transfer Function: Nearest Neighbour vs. Trilinear Filtering Figure 4: Transparency Rendering with Transfer Function: Nearest Neighbour vs. Trilinear Filtering
User's Guide	Select View Mode Slice - You can view the volume data set slice wise, in three different orientations, which can be selected by clicking on XY Plane, XZ Plane or YZ Plane. If Threshold for Slices is enabled you can view the slice as black & white image. The threshold can be changed by moving the threshold slider. The threshold modified by this slider affects also the overview mode and the threshold rendering mode. Overview - Here the volume data set is displayed as 3d object consisting of small cubes. You can rotate the object into all directions. The view direction in the overview affects all rendering operations Volume - Displays the last rendered image. Volume Renderer Render Volume - Pressing this button starts the rendering of the volume data Enable Highlights - If this option is enabled, objects with a glossy surface are generated. Image == Window - fits the rendering image size to the window size. Image Size Slider - Here you can change the rendering image size easily. Attention: changing the size destroys the last rendered image Step Length Slider - Sets the ray step length. Smaller values: better quality, less speed. Large values: bad quality, higer speed. For Transpareny Rendering, the length is fixed to 1. Rendering Mode Fast (low quality) - When enabled: High speed, but low quality. Renders the volume data using nearest neighbour values while rendering. Otherwise triliniear filtering values are used, which lead to high quality images Threshold - Generates Images of the object with a opaque surface using the threshold, which is set using the threshold slider Max Intensity - Generates maximum intensity images. only the highest density value of every ray is taken to set the pixel color Transparency - Uses the Transfer Function to generate semi transparent images Transfer Function Edit Transfer Function - Pressing this button opens the Transfer Function Window Slice Viewer - Enabling this option affects the slice viewer Rendering - Enabling this option affects the threshold rendering and the maximum intensity mode Transfer Function Window The Transfer Function used in Figure 3, Rendering Examples By clicking into the Histogram and Opacity area the opacity function can be modified. Clicking Choose Color opens the color selection window as shown in the screenshot above. There you can choose the Current Color. The Current Color can be used to modify the color bar below the Histogram and Opacity area. By clicking on Use Current Color as Background, the current color is used as background color in the Transparency Rendering Mode. The Threshold Slider can be also used to modify the treshold (blue line). It has the same effects like the threshold slider mentioned in the Select View Mode section above.