Hogwild!: A Lock-Free Approach to Parallelizing Stochastic Gradient ...
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Gradient Free Visualization with Multiple Light Approximates
MMVR2013
ked
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The difficulties of MRI visualization
The rendering results of Phong shading
CT vis. MRI vis.
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Attributed to unreliable gradient
Caused by Noise Numerical errors
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Unreliable gradient
Caused by Noise Numerical errors
Org. Estimated gradient
![Page 5: Gradient free](https://reader033.fdocuments.us/reader033/viewer/2022052601/559600e21a28ab89308b47e3/html5/thumbnails/5.jpg)
Unreliable gradient
Occurs in the region of low magnitude Affected by noise
Org. Estimated gradient
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Traditional visualization
Depends on gradient information Noisy rendering result
Org. Estimated gradient Phong shading
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Gradient-free visualization
Gets rid of the tricky estimation Improves the quality
Org. Estimated gradient Phong shading
Gradient-free
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Two pass approach
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Our method: the first pass
Off-line processing Accumulates attenuation maps for orthogonal
directions
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Our method: the second pass
Real-time interaction Lights are linearly interpolated to approximate the
contribution of attenuation maps
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Derived from
Integral of volume rendering
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Derived from
Integral of volume rendering
Color Attenuation
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Attenuation map:pre-computed summation Integral for volume rendering
+xSmoothing function
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Attenuation map:opposite direction Integral for volume rendering
-x +xvmax
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6 orthogonal att. maps
-x +x
+y
-y-z
+z
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Approximation of a light
Tx
Ty
D
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Multiple light sources
Summation of contribution
from each light
Shading = lighting x color
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Global attenuation factor
Att. factor
Small: uniform lighting Large: surface enhancement
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Lighting results
Lighting can improve spatial perception Our approach provides more details
No lighting Z lighting 3-point + head lights
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Explorative model: plane cutting
Before After
Voxel of the cutting plane
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Explorative models: modified MIP
Rewrites the integral of volume rendering
Spatial information is majorly provided by the lighting
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Explorative models: modified MIP
Similar to the effect of MIP Contains more spatial information
Org.
Modified MIP
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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
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Demo
http://www.youtube.com/watch?v=2rois9seJDw http://www.youtube.com/watch?v=ZsZAcTGDyuA
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The other results
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Thx.