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

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 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

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
Use human visual system to determine performance we need

5. Contrast Step Curves
PQ: Most efficient use of bits throughout entire range
PQ is based on Barten CSF model, but:
Modeled with an invertible function
Parameters optimized for 12bit extended color volume

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
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