Scott Miller, Dolby - Hollywood Post Alliance

Report
MovieLabs Proposals: An
Extended Dynamic Range
EOTF
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
 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
MovieLabs Proposals: An Extended Dynamic Range EOTF
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Why is a new EOTF needed?
 Ideally, the EOTF should be defined by the human visual
response – 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 relatively
low luminance levels and small dynamic ranges
 But higher dynamic ranges are just around the corner
MovieLabs Proposals: An Extended Dynamic Range EOTF
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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
 Use human visual system to determine performance we need
MovieLabs Proposals: An Extended Dynamic Range EOTF
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Contrast Step Curves
PQ: Most efficient use of bits
throughout entire range
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Barten Contrast Sensitivity Function (CSF)
1
CSF =
=
mt
k = 3.0
M opt ( u ) k
2æ 1
1
u2 ö æ 1
F0 ö
+
+
+
2
2
2 ֍
T çè X02 Xmax
N max
ø è h pE 1- e-(u u0 ) ÷ø
M opt ( u ) = e-2 p s u
2 2 2
s = s 02 + ( Cab d )
(
2
d = 5 - 3tanh 0.4 log ( L X02 40 2 )
(
)
p d2
2
4
E=
L 1- ( d 9.7 ) + ( d 12.4 )
4
)
s 0 = 0.5 arc min
Cab = 0.08 arc min mm
T = 0.1 sec
X max = 12°
N max = 15 cycles
h = 0.03
F 0 = 3 ´10 -8 sec deg 2
u0 = 7 cycles deg
p = 1.25 ´10 6 photons sec deg 2 Td
MovieLabs Proposals: An Extended Dynamic Range EOTF
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Perceptual Quantizer (PQ) EOTF
2610 1
´ = 0.1593017578125
4096 4
2523
m2 =
´ 128 = 78.84375
4096
3424
c1 =
= 0.8359375
4096
2413
c2 =
´ 32 = 18.8515625
4096
2392
c3 =
´ 32 = 18.6875
4096
m1 =
æ N m2 - c ö
1
L=ç
÷
1
çè c - c N m2 ÷ø
2
3
1
1
m1
MovieLabs Proposals: An Extended Dynamic Range EOTF
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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
MovieLabs Proposals: An Extended Dynamic Range EOTF
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Gamma 2.4 Code Words
MovieLabs Proposals: An Extended Dynamic Range EOTF
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Perceptual Quantizer (PQ) Code Words
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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
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Standardization
 This EOTF has many potential use cases for baseband and compressed video
 Similar to the many traditional uses of gamma
 MovieLabs proposal: 10,000 cd/m2 peak, 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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