High Quality Silhouette Illustration for Texture

Based Volume Rendering, Nagy and Klein

Extracting and Rendering Volume Data Silhouettes

• Problem

• Nagy & Klein Basic Approach

• Critical Analysis

Problem

• Huge datasets

• Noisy datasets

• Need efficient and robust technique

Silhouette Extraction Techniques

• Front-face/Back-face Polygonal models

• Image processing

• Surface angle (lots of pre-processing)

Surface Angle

• Compute gradient at each voxel using first order central differences

• Evaluate <V,G> == 0 for each voxel to test silhouette

• What is the gradient when dealing with volume data?

• Why does <V,G> == 0 give us a silhouette?

Nagy & Klein Approach

• Hybrid of front/back facing & image processing techniques

• Processed on GPU• Identify contour

pixels• Identify silhouette

pixels

Nagy & Klein Approach

• Silhouette broadening performed on CPU

• Apply a Gaussian filter on image using convolution

• Use FFT to perform fast convolution

Results

• Engine dataset• Bonsai tree dataset• Skull dataset

Results

• Engine dataset• Bonsai tree dataset• Skull dataset

Results

• Engine dataset• Bonsai tree dataset• Skull dataset

Analysis

• Extraction is very fast (GPU processing)

• Guarantees silhouette width of one pixel

• Silhouettes are smooth and continuous

• Only extracts silhouette of most external iso-surface

• Cannot reveal any internal details

Analysis

• Volume rendering by nature is meant to reveal internal details