Screen-Space Perceptual Rendering of Human Skin

birdsowlSoftware and s/w Development

Dec 2, 2013 (3 years and 8 months ago)

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Arunkumar

Devadoss

Course Name: Applied Percept in Computer Graphics
and Visualization

Prof. :
Reynold

Bailey



Introduction



Subsurface Scattering of Light


Described in terms of Bidirectional Scattering Surface
Reflectance Distribution Function (BSSRDF).



Human Skin : Computer Graphics
vs

Cinematography



Existing Algorithms

blurring of high frequency
details in texture space




Issue: Scalability Issue due to complexity of scene.


Previous Work


Texture space diffusion:


Blur effect using kernels by means of Poisson Sampling and
single Gaussian Blurring.



Perception of Translucency:


Easy to pickup by the visual system.




Proposed Solution



Post
-
Processing
-

Produce scattering effect in Screen
Space instead of Texture Space.



Complexity : Less information to work in 2D Screen
space than the Texture space.

Screen Space Algorithm

Process Flow


Convolution process with 6 2D convolution jittered
samples and 6 1D Gaussians kernels, combining them
with a weighted sum in the second pass.


Kernels are chosen based on :


Pixel away from the object ,

narrow kernel is used.


Greater Gradient in the depth

map, narrow kernel is used.

The equation for determining stretch factor is:



Process Flow


For
specular

component , the
Kelemen/Szirmay
-
Kalos

model in addition to bloom filter.



Convolution is applied in pixel
shader

selectively using
the matte mask.





Texture Space
vs

Screen Space

Texture Space

Screen Space

Special methods are required to
bring back the optimizations like
Back Face Culling and Viewport
clipping.


The optimizations are implicit.


Requires Per
-
Character
irradiance map

for processing
.

All Subjects are processed at the
same time.

Unclear how to use the GPU for
early Z
-
rejection

to avoid
overdraw , and optimize the
convolution process.

Depth pass is

discarded.

Pixels

may be mapped to the
same position from texture space
to screen space.

Works in screen space directly,

no mapping involved.

Texture Space

Screen Space

Adjacent points in 3D world
space

may not be adjacent in
screen space. This produces
errors in texture
-
space diffusion.


Not applicable

in screen space.


Limitations of Screen Space


Fails to simulate lighting on highly curved surfaces.


Errors produced in the form of small haloes around
some areas of the model.

Results


Psychophysical
Experiment


The algorithm outperforms other two algorithms when compared against TS.


Minimal difference between TS and SS Full.


Faster performance with SS full with good scalability.

No

SSS


Rendered without
Screen Space

TS


Texture Space Algorithm.

SS Jittered


Screen Space
Adaption with Jittered
samples.

SS Full


Proposed Algorithm


Demo


Texture Space


Screen Space




Reference

Jimenez, J., Sundstedt, V., and Gutierrez, D. 2009. Screen
-
space perceptual rendering of human skin. In
Proceedings of the 6th Symposium on Applied Perception in Graphics and Visualization

(Chania, Crete, Greece,
September 30
-

October 02, 2009). S. Spencer, Ed. APGV '09. ACM, New York, NY DOI=
http://doi.acm.org/10.1145/1620993.1609970






Questions ??

Thank You