Photographic Tone Reproduction for Digital Images
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1 Photographic Tone Reproduction for Digital Images Brandon Lloyd COMP238 October 2002
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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 - PowerPoint PPT Presentation
Transcript of Photographic Tone Reproduction for Digital Images
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Photographic Tone Reproduction for Digital Images
Brandon Lloyd
COMP238October 2002
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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
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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
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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
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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
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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:
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Luminance Scaling
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Luminance Scaling
• Control burn out of high luminances
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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
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Automatic Dodging-and-Burning
• The effects of using different scales
Center
Surround
s1
s2
s3
s1 s2 s3
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Automatic Dodging-and-Burning
• Use difference of Gaussians for center-surround function
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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
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Automatic Dodging-and-Burning
Details recovered by using dodging-and-burning
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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
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Results
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Results
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Results
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Comparison
Durand et al. Reinhard et al.
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Comparison
Durand et al. Reinhard et al.
