DVR08_2 - Visualization Methods Contour Tracking Surface...

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1 1 Visualization Methods Contour Tracking Surface Rendering Direct Volume Rendering Iso-surface Rendering 2 What is Volume Visualization Data Set Volume data Image illumination
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2 3 What is Volume Visualization Render volume without extracting any surfaces (DVR) a method of displaying volumetric data as a two-dimensional image the primary goal is to enhance the visual understanding of the data set instead of photo realism 4 Basic Idea of DVR Based on the idea of ray tracing Treat each pixel as a light source Emit light from the image to the object space The ray stops at the object boundary Calculate shading at the boundary point Assign the value to the pixel
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3 5 Volume Rendering Parameters Opacity O% (Transparent) to 100% (Obscured) Color Density threshold Set the range of density including interesting objects 6 Applications
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4 7 Applications 8 Volume Rendering Features Insensitivity to object/scene complexity rendering performance depends mainly on the constant resolution of the volume buffer suitable for objects that are hard to render using conventional graphics system
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5 9 Viewpoint independence Samples and simulated dataset Inner information Block operations support Boolean and block operations and CSG Volume Rendering Features 10 Memory size of volume data: Processing power Discrete form Lack of geometric information VR Weakness MB 137 Bytes 2 512
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6 11 Image-based (backward projective) Ray-casting Object-based (forward projective) Cell projection, shear-warp, splatting, texture-based algorithms VR Classification 12 Volume rendering pipeline Data Acquisition Segmentation Gradient Computation Classification Shading Compositing
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7 13 Data Acquisition Acquisition techniques MRI (Magnetic Resonance Imaging) (3D) Ultrasound CT (Computed Tomography) fMRI, PET Industrial Scanners 14 Data Representation 3D volume data are represented by a finite number of cross sectional slices (a stack of images) N x 2D array = 3D array index Density (16-24bits) Pixel:
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8 15 Data Representation What is a Voxel? two definitions A voxel is a cubic cell, which has a single value covering the entire cubic region A voxel is a data point at a corner of the cubic cell. The value of a point inside the cell is determined by interpolation 16 original data voxel data (gray value) the value of voxel(x,y,z): resample(x,y,z), if (x,y,z) is a grid location OR interpolating samples Voxelization
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9 Recover the original continuous function from discrete samples Box filter Hat filter Sinc filter Interpolation 18 zero-order interpolation Interpolation Interpolation by 0.7*s1 + 0.3*s2 0 7 10 10 0 7 7.3 7.9 0 5.6 7 7 0 0 2.1 2.8 We expect blue!
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This note was uploaded on 04/29/2010 for the course CSE 4190.410 taught by Professor Shinyeonggil during the Spring '09 term at Seoul National.

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DVR08_2 - Visualization Methods Contour Tracking Surface...

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