• Problem
  • World HDR
    • 8 or more orders of magniitude base 10(1 with 8 zeros after) (sun, lights, moon,stars)(27 ev about)
      
      • 6 or more in a given scene often (20 ev)
        
  • Human visual system
    • 5 orders magnitude in scene (20 EV)
      
    • 10 with adaptation
      
  • Film -- about 3 orders of magnitude basic (10.5 ev)
    
  • Digital--top camera  (14 ev)
    
  • paper,slide show, monitor about 2 orders of magnitude (7 ev)
  • Need to have enough different shades to capture range -- otherwise posterizing
    

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• Solutions:
  • Live with it
  • Cheat the eye into thinking more range in paper, monitor etc than you have. To do this you have to know/capture the high range to work with. May mean needing more accuracy than 256 levels too. 
    • nerves are typically center surround so if have light surrounded by dark light will look brighter.
    • artists use this artistically
    • Tone mapping with film: eg. zone system of Ansel Adams(look under images in google search)-film higher dynamic range than paper
      
      • expose for darks, develop for the bright is a form of global tone mapping that just remaps range into negative density
      • burning and dodging give local tone operator
      • just digitally compress bigger range into 256 range of digital work - lose contrast

      
      

      
      
      
      
  • Digital
  • Take many pictures at different exposure levels
  • Combine them into a format that can express all the full dynamic range without posterizing
  • demo posterizing with pepper (flatten)
    
  • The gray scale is most important
    
  • edit --> convert to profile--- put in Lab space 
  • Color balance Green-- Magenta is the a channel and blue--yellow is the b channel
  • In channels blur Lightness, a and b
  • we see lightness dominates for acuity
  • posterizing messes up color in channels but not accuity
  • Now have artist problem of tone mapping
    

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• Why do we care:
  • more interesting images
  • Hollywood -- initially get people back to theaters
  • security -- no hiding
  • games
  • art
  • more manipulative possibilities with images
  • lighting (later)

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• How do we aquire images:
  • scan negative several times-- trouble
    
  • take pictures at several exposures
    • not great if subject moves
  • new cameras and chips

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