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Photographic Tone Reproduction for Digital Images. Brandon Lloyd COMP238 October 2002. The range of light in the real world spans 10 orders of magnitude! A single scene’s luminance values may have as much as 4 orders of magnitude difference

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problems with high dynamic range hdr
The range of light in the real world spans 10 orders of magnitude!

A single scene’s luminance values may have as much as 4 orders of magnitude difference

A typical CRT can only display 2 orders of magnitude

Tone-mapping is the process of producing a good image of HDR data

Problems with High Dynamic Range (HDR)
zone system
Zone System
  • Used by Ansel Adams. Utilizes measured luminance to produce a good final print
  • Zone: an approximate luminance level. There are 11 print zones
  • Middle-grey: Subjective middle brightness region of the scene, typically map to zone V
  • Key: Subjective lightness or darkness of a scene
zone system4
Zone System
  • Measure the luminance on a surface perceived as middle-gray - map to zone V
  • Measure dynamic range from both light and dark areas.
  • If dynamic range < 9 zones then full range can be captured in print
  • Otherwise dodging-and-burning must be used to bring out details
  • Dodging-and-burning: Witholding or adding light in development to lighten or darken the final print
algorithm
Algorithm
  • First apply a scaling to the whole image. This similar to setting the exposure for mapping to middle-gray
  • Apply automatic dodging-and-burning to compress dynamic range if necessary
luminance scaling
Luminance Scaling
  • Use log-average luminance to approximate the key of the scene
  • In a normal-key image middle-gray maps to a key value a = .18 suggesting the function:
luminance scaling8
Luminance Scaling
  • Control burn out of high luminances
automatic dodging and burning
Automatic Dodging-and-Burning
  • Think of this as local adaptation, choosing a key value for every pixel
  • Need a properly chosen neighborhood
  • Dodging-and-burning is applied to regions bounded by large contrasts
  • Use center-surround functions to measure local contrast at different scales
automatic dodging and burning10
Automatic Dodging-and-Burning
  • The effects of using different scales

s1

s2

s3

s1

Center

s2

Surround

s3

automatic dodging and burning11
Automatic Dodging-and-Burning
  • Use difference of Gaussians for center-surround function
automatic dodging and burning12
Automatic Dodging-and-Burning
  • Choose largest neighborhood around a pixel with fairly even luminances
  • Take the largest scale that doesn’t exceed a contrast threshold:
  • Final local operator
automatic dodging and burning13
Automatic Dodging-and-Burning

Details recovered by using dodging-and-burning

results
Results
  • Used FFT to compute the Gaussians
  • 8 discrete scales ranging from 1 pixel to 43 increasing by a factor of 1.6
  •  = 0.05
comparison
Comparison

Durand et al.

Reinhard et al.

comparison19
Comparison

Durand et al.

Reinhard et al.