Computational Photography Si Lu Spring 2018 http://web.cecs.pdx.edu/~lusi/CS510/CS510_Computati onal_Photography.htm 04/05/2018
Last Time o Course overview n Admin. Info n Computational Photography 2
Today o Digital Camera n History of Camera n Controlling Camera o Photography Concepts 3
Pinhole-Camera aperture o The first camera n 5 th B.C. Aristotle, Mozi (Chinese: 墨子 ) n How does the aperture size affect the image? http://en.wikipedia.org/wiki/Pinhole_camera Modified from slides provided by L. Zhang 4
Shrinking the aperture Slide credit: L. Zhang 5
Shrinking the aperture o Why not make the aperture as small as possible o Less light gets through o Diffraction effects Slide credit: L. Zhang 6
Shrinking the aperture Slide credit: L. Zhang 7
First production camera? o 1839. Daguerrotype Slide credit: F . Durand
Beginning of hobby photography? o 1900 Kodak Brownie Slide credit: F . Durand
Color photography o Who did the first color photography? n Maxwell (yes, the same from the EM equations) o When? 1861 o Oldest color photos still preserved: Prokudin-Gorskii http://www.loc.gov/exhibits/empire/ Slide credit: F . Durand
Prokudin-Gorskii o Digital restoration http://www.loc.gov/exhibits/empire/ Slide credit: F . Durand
Prokudin-Gorskii Slide credit: F . Durand
Prokudin-Gorskii Slide credit: F . Durand
Deep Learning? Zhang, Richard, Phillip Isola, and Alexei A. Efros. "Colorful image colorization." European Conference on Computer Vision. Springer, Cham, 2016. 14
Flash bulb? o As opposed to powder systems o Boutan-Chauffour - 1893 o For underwater photography Slide credit: F . Durand
Instant photography? o 1947, Edwin Land (Polaroid founder) Slide credit: F . Durand
Autofocus o 1978, Konica o 1981 Pentax ME-F. o Canon T80 1985 n Canon AL1 had focus assist but no actuator o Minolta Maxxum 1985 (AF in body) Slide credit: F . Durand
First microprocessor in a camera o Canon AE-1 1976 Slide credit: F . Durand
First scanned photo? o 1957, Russell A. Kirsch of the National Bureau of Standards, 176x176 Slide credit: F . Durand
CCD technology? o 1969, Willard S. Boyle and George E. Smith, Bell Laboratories Slide credit: F . Durand
CCD in astronomy o 1979, 1-meter telescope at Kitt Peak National Observatory, 320x512, great for dim light o Nitrogen cooled Slide credit: F . Durand
Computer Graphics? Computers to create image o Sketchpad, 1961, Ivan Sutherland Turing Awardee at PSU now Slide credit: F . Durand
Paint program o Dick Shoup: SuperPaint [1972-73] n 8 bits n http://www.rgshoup.com/prof/SuperPaint/ o Alvy Ray Smith (Pixar co-founder): Paint [1975-77] n 8 bits then 24 bits http://www.alvyray.com/Awards/ n AwardsMain.htm http://www.alvyray.com/Bio/BioMain.htm n o Tom Porter: Paint Slide credit: F . Durand
Photoshop o Thomas Knoll and John Knoll began development in 1987 o Version 1.0 on Mac: 1990 http://en.wikipedia.org/wiki/Photoshop#Development o http://www.storyphoto.com/multimedia/multimedia_photoshop.html o Slide credit: F . Durand
First digital camera? 1975, Steve Sasson, Kodak o Uses ccd from Fairchild semiconductor, A/D from Motorola, .01 o megapixels, 23 second exposure, recorded on digital cassette Slide credit: F . Durand
Completely Digital Commercial camera o 1991 first completely digital Logitech Dycam 376x240 http://www.g4tv.com/ Slide credit: F . Durand
Digital o 1994 Apple quicktake, first mass-market color digital camera, 640 x 480 (commercial failure) Slide credit: F . Durand
Digital SLR? o 1992 Kodak DCS 200, 1.5 Mpixels, based on Nikon body Slide credit: F . Durand
Consumer digital SLR? o Canon D30, 2000 3MPixels Slide credit: F . Durand
Camera phone? o In November 2000 Sharp and J-Phone introduced the first camera-phone in Japan Slide credit: F . Durand
Outline o History of Camera o Controlling Camera 31
Camera specifics o Focal length o Shutter o Aperture o Reciprocity o Depth of field (focal) o Motion o ISO o Metering 32
Pinhole imaging Slide credit: F . Durand
Focal length: pinhole optics f d s Film/ sensor scene pinhole pinhole Film/ sensor Slide credit: F . Durand
Field of View 24mm 50mm 135mm Slide credit: F . Durand
Focal length: pinhole optics o What happens when the focal length is doubled? n Projected object size n Amount of light gathered f d 2f s Film/ sensor scene pinhole Slide credit: F . Durand
Perspective vs. viewpoint o Focal lens does NOT ONLY change subject size o Same size by moving the viewpoint o Different perspective (e.g. background) Slide credit: F . Durand
Perspective vs. viewpoint o Telephoto makes it easier to select background (a small change in viewpoint is a big change in background.) Slide credit: F . Durand
Perspective vs. viewpoint o Portrait: distortion with wide angle o Why? Wide angle Standard Telephoto Slide credit: F . Durand
Shutter o Most of the time, the film/sensor is protected from light When we take a picture, the shutter opens and closes, thereby o exposing the film. Exposure is proportional to o the time the shutter is open Expressed in fraction of a second o (1/60s, 1/125s, 1/250s, 1/500s, etc.) shutter Slide credit: F . Durand
Effect of shutter speed o Longer shutter speed => more light, but more motion blur o Faster shutter speed freezes motion Slide credit: F . Durand
Effect of shutter speed o Longer shutter speed => more light, but more motion blur o Faster shutter speed freezes motion Slide credit: F . Durand
Effect of shutter speed o Freezing motion Walking people Running people Car Fast train 1/125 1/250 1/500 1/1000 Slide credit: F . Durand
Shutter speed and focal length o Because telephoto “magnify”, they also magnify your hand shaking o Telephotos therefore require faster shutter speed o Rule of thumb: n The slowest shutter speed where normal human can hand-hold and get a sharp picture is 1/f n E.g., a 500mm requires 1/500 s or higher. o Solution: Image stabilization n mechanically compensates for vibration n Can gain 2 or 3 shutter speeds (1/125 or 1/60 for a 500mm) Slide credit: F . Durand
Your best friend o Use a tripod! It will always enhance sharpness Slide credit: F . Durand
Exposure o Two main parameters: n Shutter speed n Aperture (in f stop) n Shutter speed (in fraction of a second) Slide credit: F . Durand
Aperture o Diameter of the lens opening (controlled by diaphragm) o Expressed as a fraction of focal length, in f-number n f/2.0 on a 50mm means that the aperture is 25mm n f/2.0 on a 100mm means that the aperture is 50mm o Disconcerting: small f number = big aperture o What happens to the area of the aperture when going from f/2.0 to f/4.0? o Typical f numbers are f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32 Slide credit: F . Durand
Exposure o Two main parameters: n Aperture (in f stop) n Shutter speed (in fraction of a second) o Reciprocity n The same exposure is obtained with an exposure twice as long and an aperture area half as big n Reciprocity can fail for very long exposures Slide credit: F . Durand
Exposure & metering o The camera metering system measures how bright the scene is o In Aperture priority mode, the photographer sets the aperture, the camera sets the shutter speed o In Shutter-speed priority mode, the photographers sets the shutter speed and the camera deduces the aperture n In both cases, reciprocity is exploited o In Program mode, the camera decides both exposure and shutter speed (middle value more or less) o In Manual, the user decides everything (but can get feedback) Slide credit: F . Durand
Pros and cons of various modes o Aperture priority n Direct depth of field control n Cons: can require impossible shutter speed (e.g. with f/1.4 for a bright scene) o Shutter speed priority n Direct motion blur control n Cons: can require impossible aperture (e.g. when requesting a 1/1000 speed for a dark scene) o Note that aperture is somewhat more restricted o Program n Almost no control, but no need for neurons o Manual Full control, but takes more time and thinking n Slide credit: F . Durand
Metering o Photosensitive sensors measure scene luminance o Most cameras then use a center-weighted average n Can fail if scenes are very white or very black n Nikon has a more advanced system (3D matrix) Slide credit: F . Durand
Main effect of aperture o Depth of field From Photography, London et al. Slide credit: F . Durand
Depth of field Point in focus sensor lens Object with texture Slide credit: F . Durand
Depth of field o We allow for some tolerance Depth of field Point in focus sensor lens Object with texture Depth of focus Max acceptable circle of confusion Point in focus sensor lens Object with texture Slide credit: F . Durand
Slide credit: F . Durand
Depth of field o What happens when we close the aperture by two stop? Aperture diameter is divided by two n n Depth of field is doubled Diaphragm Point in focus sensor lens Object with texture Slide credit: F . Durand
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