Volume Graphics(lecture 6 : Transfer Fucntion)

slides knowledgement : G. Kindlmann

Bong-Soo Sohn

School of Computer Science and Engineering

Chung-Ang University

Transfer FunctionTransfer functions make volume data visibleby mapping data values to optical properties

volume data

Transfer Function

Optical Properties

– Anything that can be composited with a standard graphics operator (“over”)

– Opacity: “opacity functions”• Most important

– Color• Can help distinguish features

– Emittance• Why don’t we use this more often?

– Phong parameters (ka, kd, ks)– Index of refraction

Volume rendering with different transfer function

• Setting transfer function is difficult, unintuitive, and slow

Goal

• Make good renderings easier to come by– Make space of TFs less confusing– Remove excess “flexibility”– Provide one or more of:– Information– Guidance– Semi-automation– Automation

Semi-automatic generation of TF

edges

Scatter plot

Analysis

Distance Map

Whole Process

Result : CT Head

Result

Multidimensional Transfer Fucntion

1D vs 2D histogram

Volume rendering using 2D transfer function

Multidimensional transfer function

Multivariate Imaging Data

Interaction Tools

• Data Probe

• Clipping plane

• Classification Widget– Triangle– rectangle

Dual Domain Interaction

Results

Results

Results