Transcript Lens 1 - Stanford Computer Graphics Laboratory

Physically Based
Lens Flare
Phillip Ho
CS348b Final Project
Spring 2011
Final Image
What is lens flare?
 Various artifacts of optical systems
• Diffraction, internal reflection
Simulated
But why simulate an artifact?
 Dramatic effect
 Emphasize brightness
 Camera imperfections add
to realism
 Implies that an image is “un-
edited”, original footage from
the camera
Where is it used?
 Video games
 Animated feature films
 Live action films
Technical Aspects - Starburst
 Starburst pattern
 Caused by diffraction with aperture blades
 Light waves that hit small-scale geometry diffract
according to Huygens-Fresnel principle
• Points of interference become sources of spherical waves
• Resulting pattern is the superposition of these waves
http://www.cameratechnica.com/2011/02/24/how-to-create-and-avoid-starburst-highlights/
Technical Aspects - Starburst
 Represent aperture shape and imperfections as
texture maps
Technical Aspects - Starburst
 Fraunhofer approximation of power spectrum
 FFT{
}=
Technical Aspects - Starburst
 FFT computed for average wavelength 575nm
 Different wavelengths create the same pattern
at different scales
 Superimpose multiple scaled
copies at each wavelength
to get resulting starburst
Largest starburst
330nm
Smallest starburst
770nm
Technical Aspects - Starburst
 Post-processing
technique to
smooth/blur
 Superimpose
multiple copies with
random rotation and
opacity
Technical Aspects - Ghost
 Ghost artifacts
 Caused by interreflections of light
rays within lens system
 Fresnel equations determine
reflectivity
Technical Aspects - Ghost
 Trace rays through camera system
 Interreflections between each pair of interfaces
 Weight by reflectivity
 Only consider second-order
interreflections
Technical Aspects - Ghost
 Photon mapping-like implementation
 Interpolate between photons to reduce noise
Technical Aspects - Ghost
 Anti-reflective lens coating alters ghost
coloration
 Well-kept manufacturer secrets
 Solution: user-defined coloration
Lens 1:
Lens 2:
Lens 3:
Lens 4:
Lens 5:
…
Monochromatic lens flare
Colored lens flare
Technical Aspects –
Chromatic Aberration
 “Fringing” effect seen at the edges
 Light waves refract at different angles
 Refractive index varies for different wavelengths
Wavelength determines the IOR to use for Snell’s law
Technical Aspects –
Chromatic Aberration
 Split light rays into RGB components
 Cauchy’s equation
where A and B are unique
to the lens material
Putting It All Together
 Essentially more light on the sensor
 Linear Dodge (Add) in Photoshop!
Credits
 References
 Web pages
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How to Create (and Avoid) Starburst Highlights (http://www.cameratechnica.com/2011/02/24/how-to-create-and-avoid-starbursthighlights/)
Understanding Lens Flare (http://www.cambridgeincolour.com/tutorials/lens-flare.htm)
Flare (http://toothwalker.org/optics/flare.html)
Spectral Rendering (http://www.baylee-online.net/Projects/Raytracing/Algorithms/Spectral-Rendering/Material-Properties#Dispersion)
Raytracing Chromatic Aberration (http://senlinhou.wordpress.com/2010/12/07/raytracing-chromatic-aberration/)
CS348b ‘03: Rendering Glare (http://graphics.stanford.edu/courses/cs348b-competition/cs348b-03/glare/)
CS348b ’07: Realistic Camera Lens Flares (https://graphics.stanford.edu/wikis/cs348b-07/JulienChaumond/FinalProject)
 Technical Papers
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Matthias B. Hullin, Elmar Eisemann, Hans-Peter Seidel, Sungkil Lee. Physically-Based Real-Time Lens Flare Rendering. In: ACM
Transactions on Graphics, Vol. 30 (4), 2011 (Proc. SIGGRAPH).
Tobias Ritschel, Matthias Ihrke, Jeppe Revall Frisvad, Joris Coppens, Karol Myszkowski, Hans-Peter Seidel. Temporal Glare: Real-Time
Dynamic Simulation of the Scattering in the Human Eye. Proceedings Eurographics 2009, Munich 30 March—3 April 2009.
Spencer, G., Shirley, P., Zimmerman, K., and Greenberg, D.P. Physically-Based Glare Effects for Digital Images. In Proceedings of
SIGGRAPH. 1995, 325-334.
Kakimoto, M., Matsuoka, K., Nishita, T., Naemura, T., and Harashima, H. Glare Generation Based on Wave Optics. In Proceedings of
Pacific Conference on Computer Graphics and Applications. 2004, 133-142.
Questions?