点扩散函数

• Computed Fix: Geometric warp for R,G,B.
Near Lens Center Near Lens Outer Edge
Radial Distortion (e.g. ‘Barrel’ and ‘pin-cushion’) ‘pinstraight lines curve around the image center
• Smaller lens
– dimmer image – focus becomes less critical
FilmFilm-like Optics: Thin Lens Flaws
• Aberrations:
Real lenses don’t converge rays perfectly
– Use anti-vignetting filters, anti(darkest at center)
– OR Position-dependent Positionpixelpixel-detector sensitivity.
http://homepage.ntlworld.com/j.houghton/vignette.htm
Angle(θ Angle(θ,ϕ)
‘Center of Projection’
2D Sensor: WellWell-Lit 3D Scene: Pixel Grid,Film,…
Position (x,y)
Rays and the ‘Thin Lens Law’
• Focal length f: where parallel rays converge • Focus at infinity: Adjust for S2=f • Closer Focus ? Larger S2
f
S2 Thin Lens
http://webphysics.davidson.edu/Applets/Optics/intro.html
Try it Live! Physlets…
Sensor
Rays and the ‘Thin Lens Law’
• Focal length f: where parallel rays converge • Focus at infinity: Adjust for S2=f • Closer Focus ? Larger S2
• Optics:
Single focus distance, limited depth-of-field, limited field-of-view, depth-offield-ofinternal reflections/flare/glare
• Lighting:
Camera has no knowledge of ray source strength, position, direction; little control (e.g. flash)
www.swgc.mun.ca/physics/physlets/opticalbench.html
For more about color:
– Prev. SIGGRAPH courses (Stone et al.) – Good: www.cs.rit.edu/~ncs/color/a_spectr.html – Good: www.colourware.co.uk/cpfaq.htm – Good: www.yorku.ca/eye/toc.htm
• Choose the best, most expressive sets of rays,
THEN find the best way to measure them.
Useful links:
Interactive Thin Lens Demo (or search ‘physlet optical bench’)
• Sensor:
Exposure setting, motion blur, noise, response time,
• Processing:
– Quantization/color depth, camera shake, scene movement…
Conclusions
• Film-like photography methods limit digital photography to Filmfilmfilm-like results or less.
FilmFilm-like Color Sensing
• Visible Light: narrow band of e’mag. spectrum • λ ≈ 400-700 nm (nm = 10-9 meter wavelength) 40010• (humans:<1 octave honey bees: 3-4 ‘octaves 3do honey bees sense harmonics, see color ‘chords’ ?
• Spherical: edge rays ≠ center rays • Coma: diagonal rays focus deeper at edge
http://www.nationmaster.com/encyclopedia/Lens-(optics)
Lens Flaws: Chromatic Aberration
1-Chip Color Sensing: Bayer Grid
• Estimate RGB
at ‘G’ cels from neighboring values
http://www.cooldictionary.com/ words/Bayer-filter.wikipedia
Polarization
Course 15:
Computational Photography
A.3: Understanding Film-like Photography FilmTumblin
Computational Photography
A3: Understanding FilmFilm-Like Photography
RGB spectral curves Vaytek CCD camera with Bayer grid
www.vaytek.com/specDVC.htm
Color Sensing
• 3-chip: vs. 1-chip: quality vs. cost 1-
http://www.cooldictionary.com/words/Bayerhttp://www.cooldi tionary.com/words/Bayer-filter.wikipedia
• color fringes near edges of image http://www.swgc.mun.ca/physics/physlets/opticalbench.html •
Chromatic Aberration
• Lens Design Fix: Multi-element lenses MultiComplex, expensive, many tradeoffs!
• Rays are REVERSIBLE.
Helmholtz reciprocity
Ray bundles? Not so much: falls quickly with angle,area growth…
FilmFilm-like Photography: Many Limitations
Scene
f
f
S2 Thin Lens
http://webphysics.davidson.edu/Applets/Optics/intro.html
S2
Try it Live! Physlets…
Sensor
Not One Ray, but a Bundle of Rays
Lens Sensor
• Broaden, unlock our views of photography: • 4-D, 8-D, even 10-D Ray Space holds the photographic 810signal. Look for new solutions by creating, gathering, processing RAYS, not focal-plane intensities. focal-
Sunlit haze is often strongly polarized. Polarization filter yields much richer sky colors
RAYS and PROCESSING
• ONE Ray carries doubly infinitesimal power:
Ray bundles with finite, measurable power will:
• Span a non-zero area non• Fill a non-zero solid angle non-
• Everything is Linear: (HUGE win!)
Ray reflectance, transmission, absorption, scatter*…
Vignette Effects
Bright at center, dark at edges. Several causes compounded:
• Edge pixels span smaller angle and center pixels • Ray path length is longer off-axis off• Internal shadowing • Compensation:
Basic Ray Optics: Lens Aperture
For the same focal length:
• Larger lens
– Gathers a wider ray bundle: – More light: brighter image – Narrower depth-of-focus depth-of-
or ‘from 2D Pixels to 4D Rays’ Rays’
(10 minutes)
Jack Tumblin Northwestern University
百度文库
Naïve, Ideal Film-like Photography FilmSensor: Sensor: a film emulsion, : or a grid of light meters (pixels)
Scene
Aperture
• BUT Ray model isn’t perfect: ignores diffraction • Lens, aperture set the point-spread-function (PSF) point-spread(How? See: Goodman,J.W. ‘An Introduction to Fourier Optics’ 1968)
Equiluminant Curve defines ‘luminance’ vs. wavelength
http://www.yorku.ca/eye/photopik.htm
FilmFilm-like Color Sensing
• Visible Light: narrow band of emag spectrum • λ ≈ 400-700 nm (nm = 10-9 meter wavelength) 40010• At least 3 spectral bands required (e.g. R,G,B)
• Dispersion: wavelength-dependent refractive index wavelength– (enables prism to spread white light beam into rainbow)
• Modifies ray-bending and lens focal length: f(λ) rayf(λ