Gradient Free Visualization with Multiple Light Approximates

MMVR2013

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The difficulties of MRI visualization

The rendering results of Phong shading

CT vis. MRI vis.

Attributed to unreliable gradient

Caused by Noise Numerical errors

Unreliable gradient

Caused by Noise Numerical errors

Org. Estimated gradient

Unreliable gradient

Occurs in the region of low magnitude Affected by noise

Org. Estimated gradient

Traditional visualization

Depends on gradient information Noisy rendering result

Org. Estimated gradient Phong shading

Gradient-free visualization

Gets rid of the tricky estimation Improves the quality

Org. Estimated gradient Phong shading

Gradient-free

Two pass approach

Our method: the first pass

Off-line processing Accumulates attenuation maps for orthogonal

directions

Our method: the second pass

Real-time interaction Lights are linearly interpolated to approximate the

contribution of attenuation maps

Derived from

Integral of volume rendering

Derived from

Integral of volume rendering

Color Attenuation

Attenuation map:pre-computed summation Integral for volume rendering

+xSmoothing function

Attenuation map:opposite direction Integral for volume rendering

-x +xvmax

6 orthogonal att. maps

-x +x

+y

-y-z

+z

Approximation of a light

Tx

Ty

D

Multiple light sources

Summation of contribution

from each light

Shading = lighting x color

Global attenuation factor

Att. factor

Small: uniform lighting Large: surface enhancement

Lighting results

Lighting can improve spatial perception Our approach provides more details

No lighting Z lighting 3-point + head lights

Explorative model: plane cutting

Before After

Voxel of the cutting plane

Explorative models: modified MIP

Rewrites the integral of volume rendering

Spatial information is majorly provided by the lighting

Explorative models: modified MIP

Similar to the effect of MIP Contains more spatial information

Org.

Modified MIP

Experiments

Dataset Data resolution

Att. map resolution

Pre-computing(s)No avg. / avg.

Real-timeFPS

MRI brain 256x256x109 200x200x170 6 / 16 12.5

CT head 256x256x113 200x200x177 7 / 17 9.1

CT chest 384x384x240 200x200x125 5 / 13 10.0

Acer Aspire 8950G 2GHz Quad Core CPU 4G memory AMD RadeonHD 850M GPU

Demo

http://www.youtube.com/watch?v=2rois9seJDw http://www.youtube.com/watch?v=ZsZAcTGDyuA

The other results

Thx.