Intelligent Photography in a digital age

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Intelligent Photographyin a digital age

• February 11, 2008

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Goals

• Learn a little about photography
• Understand how basic camera systems work
• AF auto focus
• AE auto exposure
• Recognize intelligent features
• Show how neural nets and fuzzy logic are used in
  digital cameras

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Outline

• Brief history of the camera
• How a digital camera works
• Challenges in digital photography
• Intelligent features in todays digital cameras
• Case studies
• Using fuzzy logic and neural nets

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History of the Camera

• Pinhole cameras/camera obscura
• 1000 AD Ibn al-Haytham

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History of the Camera

• Wet Plate Cameras
• 1100 early 1800s
• Discovery of silver nitrate, silver chloride,
  diaphragm, photochemical effect
• 1825-1827 Joseph Nicephore Niepce
• The first photographs
• Used a pewter place coated with bitumen and
  exposed to light

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History of the Camera

• Wet plate cameras
• 1836 Louis Jacques Daguerre
• Daguerreotype camera
• Copper plate coated with silver, treated with
  iodine vapor
• Developed using mercury vapor and fixed with a
  salt solution
• 1840 William Fox Talbot
• Calotype camera

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History of the Camera

• Dry plate cameras
• 1855 von Monckhoven
• Collodian dry plates
• 1871 Richard Maddox
• Gelatin dry plates
• Began to rival wet plates
• Pros photographers could use commercially made
  dry plates instead of preparing their own
  emulsions in a mobile dark room
• Allowed cameras to be small enough to be
  hand-held
• Shortened exposure times lead to invention of the
  shutter

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History of the Camera

• Photographic Film
• 1885 George Eastman
• invented paper film
• 1888 Kodak camera
• Simple box camera
• Fixed-focus lens with single shutter speed
• Low cost brought photography to the masses
• Preloaded with 100 exposures, had to be returned
  to the factory for processing and reloading
• 1889 celluloid film
• 1910 Kodak Brownie
• Simple and inexpensive enough to introduce the
  snapshot
• On sale until the 1960s

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History of the Camera

• First Modern Cameras
• 1925 Leica 1
• Introduced 35mm film
• 1928 Rolleiflex medium format TLR
• 1933 Exakta SLR

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History of the Camera

• The Modern Camera
• 1938 Super Kodak Six-20
• First auto-exposure camera
• 1948 Polaroid Model 95
• First instant picture camera
• 1960 TTL metering
• 1977 Konica C35AF
• First mass produced AF point and shoot
• 1978 Polaroid SX-70
• First AF SLR
• 1981 Pentax ME-F
• First 35mm AF SLR
• Utilized a motorized lens
• 1986 Minolta Maxxum 7000
• Integrated AF system

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History of the Camera

• The Digital Camera
• 1986 Canon RC-701
• First analog digital camera
• First used by USAToday for the 1986 World Series
• Poor quality, could transmit pictures over the
  phone
• 1988 Canon RC-250 Xapshot
• Analog camera marketed to consumers
• 1990s introduction of the digital PS
• 1999 Nikon D1
• 2.74MP, first professional digital SLR
• 2003 Canon 300D (digital rebel)
• First DSLR under 1000
• 2007 Canon 40D
• First live view DSLR

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How a digital camera works

• Digital/Film cameras use the same principles
• Lens
• Aperture
• Shutter
• Film/Sensor

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How a digital camera works

• Lenses
• Fixed-focus, fixed-zoom (disposable cameras)
• Optical zoom
• Removable lenses
• Primes
• Zooms
• Image stabilized lenses

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How a digital camera works

• Aperture the hole or opening in a lens through
  which light is admitted
• Controls depth of field
• Measured in f-stops

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How a digital camera works

• Shutter
• Opens to expose the film or sensor to light
• Closes to stop exposure
• Shutter times measured in seconds
• i.e. 1/100, 1/50, 1/20, 1/10, 1/5, ½, 1, 2, 4, 8
• Also measured in stops of lights

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How a digital camera works

• Film
• 35mm
• Windable
• ISO speed films sensitivity to light
• ISO 400, 200, 100
• Higher ISO, faster the film. Lower ISO, slower
  film.
• Higher ISO, film is more grainy
• Sensors
• Like film, different sizes
• Crop sensors/full frame sensors
• ISO sensitivity like film
• Two types
• CCD charge coupled device, analog shift
  register
• CMOS - complementary metaloxidesemiconductor
  digital recorder
• Requires less power, less susceptible to noise

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How a digital camera works

• Exposure
• combination of shutter speed, aperture, and film
  speed (ISO)
• Correct Exposure
• a combination of shutter speed, aperture, and ISO
  that provides a correctly exposed image
• Underexposure too dark
• Overexposure washed out
• Example filling a glass of water from a faucet

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Exposure

• For any given situation, there are many
  creatively correct exposures
• Seven different kinds of creative exposure
• Story telling small apertures (f/32, f/22,
  f/16)
• Isolation large apertures (f/2.8, f/4, f/5.6)
• Who cares in between apertures, depth of field
  isnt a concern
• Macro out of focus backgrounds (bokeh)
• Freeze action fast shutter speeds (1/1000,
  1/500, 1/250)
• Panning medium shutter speeds (1/60, 1/30)
• Imply motion snow shutter speeds (1/4, ½, 1)

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Exposure

• A Stop of light a doubling or halving of
  light
• One stop of light is equal to another
• One f-stop
• One ISO stop
• One shutter stop
• Can trade one stop for another to keep the same
  exposure
• Sunny f/16 rule on a sunny day, f/16 and 1/ISO
  to give correct exposure

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Challenges in Digital Photography

• Technological issues
• File types
• Auto Focus
• Auto Exposure
• Noise Reduction
• Sharpness
• Contrast
• White Balance

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Challenges in Digital Photography

• File Types
• JPEG joint photographic experts group
• Most commonly used format for web and digital
  cameras
• Pros used everywhere, small file sizes, good
  compression, fit more on a memory card, faster
  download times
• Cons lossy compression leads to data loss and
  image degradation from resaving
• TIFF tagged image file format
• Pros lossless image compression, no image
  degradation
• Cons not universally supported, large image
  sizes, still lose some information and ability to
  process photos
• RAW camera proprietary format
• Each camera has its own format
• Pros full control over image processing,
  smaller files than TIFF, completely lossless, no
  compression
• Cons almost no support, formats constantly
  changing, must do all processing manually

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Challenges in Digital Photography

• Auto-Focus
• Active methods independent of the optical
  system
• IR and ultrasounds
• Work in low light, low contrast situations, will
  not work through glass or water
• Passive methods uses analysis of the image
  itself
• Phase Detection and Contrast Measurement
• More accurate, will work through glass, bad in
  low light or low contrast situations, allows for
  high numbers of focus points
• Can only be used with digital cameras

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Challenges in Digital Photography

• Auto Focus how does it work?
• Active
• Sends a signal towards target
• Measures returning signal
• Calculates distance
• Drives lens to desired position

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Challenges in Digital Photography

• Auto Focus how does it work?
• Passive
• Looks at current image
• Move lens slightly, compare the two images
  (sharpness, contrast)
• If better, keep moving. If worse, go other
  direction

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Challenges in Digital Photography

• Auto Exposure choosing the correct exposure
• Metering Techniques
• Spot only measures in a 2-3 degree cone in the
  center of image
• Center Weighted weights the center 50-60 of
  the image
• Average averages the entire scene
• Partial only uses a certain region (usually the
  center)
• Evaluative uses information from several
  zones and combines the info to find the best
  exposure
• Scene Modes gives the camera an idea of what it
  is seeing so it can apply special rules when
  metering (night, indoors, museum, snow, sports)

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Challenges in Digital Photography

• Auto Exposure how does it work?
• 1. Exposure mode measures incoming light
• 2. Calculates exposure so that scene is
  approximately 18 gray
• 3. Calculates minimum shutter speed based on lens
  focal length
• 4. Calculates required aperture for min shutter
  speed
• 5. If not possible, add stops from ISO
• 6. If necessary, shoot with aperture wide open

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Challenges in Digital Photography

• 18 gray card, AE
• White card, AE
• White card, ME
• Black card, ME
• Black Card, ME
• Black, Gray, and White cards, AE

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Intelligent Cameras

• Todays digital cameras have many intelligent
  capabilities
• Fuzzy Logic systems
• Auto exposure decision making
• Focus point selection
• Passive auto focus
• Neural systems
• Evaluative or matrix metering
• Face detection

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Intelligent Cameras

• Auto Exposure Decision Making
• Once an exposure has been calculated (using any
  of the metering methods) must then choose the
  creatively correct exposure
• Fuzzy rules based on
• Available ISOs, shutter speeds, and apertures
• Weights or priorities given to different settings
• Example Auto depth of field, action, museum modes

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Intelligent Cameras

• Focus Point Selection
• Most newer cameras have multiple focus points
• Must choose which focus point you intended the
  camera to use
• Fuzzy logic rules
• If 1 is near and 2 and 3 is far, 1 is somewhat
  likely
• If 1 is near and 2 is near and 3 is far, 1 and 2
  are highly likely
• If 1 and 3 are far and 2 is near, 2 is highly
  likely
• Ect.

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Intelligent Cameras Case Study

• Passive Auto-focus using Fuzzy Logic
• Image is compared as lens focuses to choose the
  best image
• Using a sharpness measure
• Define over a portion of the image
• Use fuzzy membership functions and rules to drive
  the lens

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Intelligent Cameras Case Study

• Passive Auto-focus
• Fuzzy rules
• If sharpness is increasing fast, move lens fast
  in same direction
• If sharpness is increasing slowly, move lens
  slowly in same direction
• If sharpness is not changing, do not move lens
• If sharpness is decreasing, move lens lowly in
  opposite direction
• Use Matlabs Fuzzy Logic toolbox to easily model
  this system

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Case Study

• Face Detection via neural network