Optics Real-time Rendering of Physically Based Optical Effects in Theory and Practice Masanori KAKIMOTO Tokyo University of Technology

Table of Contents Introduction Basic geometrical optics Brief overview of wave optics Conclusion

INTRODUCTION Real-time Rendering of Physically Based Optical Effects in Theory and Practice Optics

Physics on Lights Optics –Geometrical optics – a simple, practical model –Wave optics – more physically correct and complicated Electromagnetism – a classical physics model Quantum optics – a modern physics model

Optics and Computer Graphics Theories Computer graphics theories are based on optics –Vast majority of the theories and techniques upon geometrical optics –~1% taking wave optics into account Photon mapping borrows a concept ‘photon’ from quantum optics and use it in a geometrical optics framework

Topics This course –Most topics are related with geometrical optics –Some are wave optics related This talk covers: –Basic g.o. knowledge for the rest of the course –Brief introduction of wave-related topics for a later talk

BASIC GEOMETRICAL OPTICS Real-time Rendering of Physically Based Optical Effects in Theory and Practice Optics

Geometrical Optics Models for CG Pinhole camera model Thin lens approximation Thick lens approximation Full lens system

Geometrical Optics Models for CG Pinhole camera model Thin lens approximation Thick lens approximation Full lens system + thickness + aperture + approximated refraction + accurate refraction + multi-wavelengths etc.

Geometrical Optics Models and Effects Geometrical optics Thin lens / Thick Lens Full simulated lens Pinhole Perspective projection Motion blur Bokeh (defocus) Focus breathing Complex Bokeh Chromatic aberration Optical vignetting Lens ghosts + aperture + approximated refraction + accurate refraction + multi wavelengths Natural vignetting

Geometrical Optics Models and Effects Geometrical optics Thin lens / Thick Lens Full simulated lens Pinhole Bokeh (defocus) Focus breathing Complex Bokeh Chromatic aberration Optical vignetting Lens ghosts + aperture + approximated refraction + accurate refraction + multi wavelengths Natural vignetting Today’s topics

Geometrical Optics Models and Implementations Graphics HW (fixed pipeline) Ray tracing Accumulation buffer Programmable shader techniques Wavefront tracing Post processing Geometrical optics Pinhole + aperture + accurate refraction Full lens system Thin lens / Thick Lens Distribution Ray tracing

Geometrical Optics Models and Implementations Today’s topics (geometrical optics) Programmable shader techniques Post processing Geometrical optics Pinhole + aperture + accurate refraction Full lens system Thin lens / Thick Lens Wavefront tracing

Thin Lens – Fundamentals to Understand Real-Time Special Effects Real-time techniques are based on thin lens theory –Many optical effects accounted for by thin lens –Some effects derived from full lens system model Each can be mimicked by real-time techniques (extended thin lens theory)

Thin Lens Model optical axis (principal axis) focal point focal length principal plane incident light ray center of lens (principal point) effective aperture diameter

Thin Lens Approximation – Rule 1 Incident light rays parallel to the principal axis always go through the focal point optical axis (principal axis) focal point focal length principal plane incident light ray center of lens (principal point)

Thin Lens Approximation – Rule 2 Incident light rays that passed through the focal point go parallel to the axis after exiting the lens focal point focal length incident light ray

Thin Lens Approximation – Rule 3 Incident light rays through the center of the lens travel straight (never get refracted) optical axis incident light rays center of lens

Rays Converge on a Certain Plane Rays from an object at distance converge on a plane at distance forming an image object image film or sensor focus distance

Thin Lens Equation object image film

Thin Lens and Closer Objects If the object gets closer, the converging plane (film) needs be farther from the lens object image film

Thin Lens and Far Objects If the object is far, the film needs be closer to focal length image film

Film Size and FOV for Infinite Focus film : Field of view for infinite focus

Film Size and FOV for Closer Focus film : Field of view for closer focus

F-number Represents Lens Brightness film : diameter of the lens Smaller f-number means brighter image

Effective F-number film Smaller f-number means brighter image

WAVE OPTICS OVERVIEW Real-time Rendering of Physically Based Optical Effects in Theory and Practice Optics

Rays travel straight Introduction Geometrical optics – virtually correct, simple Wave optics – more physically correct, complicated Geometrical opticsWave optics Waves propagate concentrically

Wave-Related Phenomena and Effects Diffraction –Glare –Airy disc Interference –Surface coating –Thin film color effects Polarization –Complex reflection –Image dehazing Can be simulated with extended ray theories [CookTorrance1981], [Gondek1994], [Wolff1999], [Schechner 2001] Requires wave optics Cannot simulate with extended rays Wave optics topics in this course focus on diffraction

Diffraction – A Major Cause of Glare Geometrical opticsWave optics Diffraction

Diffraction Details Later in this course Wave optics based glare generation techniques

CONCLUSION Real-time Rendering of Physically Based Optical Effects in Theory and Practice Optics

Conclusions Most computer graphics theories rely on geometrical optics –Real-time techniques basically use thin lens approximation –Effects beyond thin lens can be mimicked (later in this course, e.g., aberrations) Popular wave optics effects are based on diffraction