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Scott Miller, Dolby Labs

Scott Miller, Dolby Labs. MovieLabs Proposals: An Extended Dynamic Range EOTF. What is an EOTF and why is it so important?. EOTF stands for Electro-Optical Transfer Function It describes how to turn digital code words into visible light

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Scott Miller, Dolby Labs

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  1. Scott Miller, Dolby Labs MovieLabs Proposals: An Extended Dynamic Range EOTF

  2. What is an EOTF and why is it so important? • EOTF stands for Electro-Optical Transfer Function • It describes how to turn digital code words into visible light • The image on the reference display is what truly defines the signal • An artist makes creative decisions on what the content will look like while viewing a reference display • Could be sitting at a grading desk in a post production suite • Could be sitting in front of camera control units at a live production

  3. Why is a new EOTF needed? • Ideally, the EOTF should be defined by the human visualresponse – but our current system is defined by this: • Current “Gamma” nonlinearity based on CRT physics • Finally standardized by ITU-R Rec. BT.1886 • It is a sort of perceptual EOTF – but only at relativelylow luminance levels and small dynamic ranges • But higher dynamic ranges are just around the corner

  4. Building a new EOTF • Detailed user preference studies showed an absolute dynamic range of 0 to 10,000 cd/m2 satisfied most viewers’ desires • Assume practical system will need to be a maximum of 12 bits • Due to current infrastructure and silicon constraints • Usehuman visual system to determine performance we need

  5. Contrast Step Curves PQ: Most efficient use of bits throughout entire range

  6. Barten Contrast Sensitivity Function (CSF)

  7. Perceptual Quantizer (PQ) EOTF

  8. Doesn’t a 10,000 cd/m2 system “waste” a lot of code words that we can’t use yet • The short answer is “no” • The logarithmic shape of PQ at the top end allows substantial gains in peak brightness without costing huge numbers of code words • Think of it as headroom for further expansion • PQ headroom from 5000 to 10,000 cd/m2 = 7% of code space • Headroom above white in traditional SMPTE range gamma = 8% of code space • The midpoint of the code range for PQ represents about 93 cd/m2 • If we were using a traditional gamma function, headroom waste would be a huge problem

  9. Gamma 2.4 Code Words

  10. Perceptual Quantizer (PQ) Code Words

  11. Conclusions • We need a standardized EOTF to define a new system for extended dynamic range • PQ is the most efficient way to encode extended dynamic range • Each code value corresponds to just under a perceptual step - less wasted codes • A 10,000 cd/m2 system makes a lot of sense • The extra dynamic range is appreciated, and preferred by viewers • It gives the system headroom for display improvements in the future • No more bits are required compared to ~1000 cd/m2 systems

  12. Standardization • This EOTF has many potential use cases for baseband and compressed video • Similar to the many traditional uses of gamma • MovieLabsproposal: 10,000 cd/m2peak, XYZ color primaries, 12bit PQ • But the EOTF could also be used with other color spaces • SMPTE 10E Drafting Group working on perceptual EOTF • MPEG looking at signaling for perceptual EOTF in HEVC VUI metadata • SMPTE likely starting a High Dynamic Range / Wide Color Gamut study group in 10E as well

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