Spatial Tone Mapping in High Dynamic Range Imaging

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Spatial Tone Mapping in High Dynamic Range Imaging

• Zhaoshi Zheng

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High Dynamic Range Imaging

• Conventional digital representation of images in
  computers can not produce the color range in
  natural world
• So the techniques for capturing, storing, and
  reproducing realistic scene developed HDRI
• Sourcehttp//www.scottkelby.com/blog/?sgapw

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Tone Mapping

• Most display device can not accommodate the color
  range of HDR
• Map HDR to LDR tone reproduction, or tone
  mapping
• Spatial Operators work directly on pixels
• Others Frequency and Gradient domain

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Spatial Tone Mapping Operators

• Demonstrate inherited data level parallelism
• Good candidates for multi-threaded implementation
  on modern GPUs
• Global same mapping curve for all pixels
• Local mapping curve for each pixel depends on
  its neighbor pixels

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Tumblin-Rushmeiser Brightness-Preserving Operator
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Tumblin-Rushmeiser Brightness-Preserving Operator
(Implementation)
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Tumblin-Rushmeiser Brightness-Preserving Operator
(Implementation)
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Results (Image Comparison)

• Left Noop, direct pixel value in hdr file
• Right TR tone mapping operator, w/ scale factor
  equals 256 and saturation equals 0.8, produced by
  CPU

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GPU Naïve Implementation
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GPU Naïve Implementation
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GPU Naïve Implementation
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GPU Naïve Implementation
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Results (Image Comparison)

• Left Original CPU code released with the book,
  using double precision
• Middle Slightly modified (on data structure and
  file IO) CPU code, using single precision
• Right GPU code, using single precision.

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Results(Execution Time)
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Result(Speedup)
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Future work

• Optimization
• Vectorize computation of luminance
• Compute Log Average on GPU (tradeoffs)
• More operators
• 35 other operators, aiming at speed up

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Reference

• Eric Reinhard, Greg Ward, Sumanta Patanaik and
  Paul Debevec, High Dynamic Range Imaging