1. Physically Based Lens Flare
Phillip Ho
CS348b Final Project
Spring 2011

2. Final Image

3. What is lens flare? Various artifacts of optical systems
Diffraction, internal reflection
Simulated

4. 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

5. Where is it used?
Video games
Animated feature films
Live action films

6. 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

7. Technical Aspects - Starburst
Represent aperture shape and imperfections as texture maps

8. Technical Aspects - Starburst
Fraunhofer approximation of power spectrum
FFT{ } =

9. 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

10. Technical Aspects - Starburst
Post-processing
technique to
smooth/blur
Superimpose multiple copies with random rotation and opacity

11. Technical Aspects - Ghost
Ghost artifacts
Caused by interreflections of light rays within lens system
Fresnel equations determine reflectivity

12. Technical Aspects - Ghost
Trace rays through camera system
Interreflections between each pair of interfaces
Weight by reflectivity
Only consider second-order
interreflections

13. Technical Aspects - Ghost
Photon mapping-like implementation
Interpolate between photons to reduce noise

14. 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

15. 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

16. Technical Aspects – Chromatic Aberration
Split light rays into RGB components
Cauchy’s equation
where A and B are unique
to the lens material

17. Putting It All Together
Essentially more light on the sensor
Linear Dodge (Add) in Photoshop!

18. Credits References Web pages Technical Papers
How to Create (and Avoid) Starburst Highlights (
Understanding Lens Flare (
Flare (
Spectral Rendering (
Raytracing Chromatic Aberration (
CS348b ‘03: Rendering Glare (
CS348b ’07: Realistic Camera Lens Flares (
Technical Papers
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,
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,

19. Questions?