Scott Janus will present on the value and technical challenges of high dynamic range (HDR) and wide color gamut (WCG) displays. HDR allows for content with a wider range of brightness and more colors, but requires new displays. It provides a more realistic visual experience than standard dynamic range. Implementing HDR faces technical hurdles around representing and processing the increased brightness and color levels.

1. Scott Janus, Principal Engineer
D

2. 2

3. 3
Presentation Goals
Explain the value of High Dynamic Range (HDR) and Wide Color Gamut (WCG)
Explain the technical challenges of deploying HDR + WCG

4. 4
What is HDR?
Practically speaking:
 Content with a wider range of brightness and color
– Also an increased number of brightness and color levels
 Experiencing HDR content requires new displays

5. 5
Let’s talk about color
and brightness…
Really they are tightly
interwoven, but let’s
consider them
individually for now

6. 6
Color is
complicated

7. 7

8. 8
Monitors Can Produce a Finite Range of Colors
Typically, red, green, and blue subpixels.
If you modulate each primary 0-100%, you can
envision a three-dimensional color cube
All colors in this cube are the gamut of colors
the device can reproduce

9. 9
Let’s simplify things…
Humans are bad at perceiving
volumetric data, so compress the
color volume to two dimensions
Chromaticity Diagram

10. 10
Wide Color
• Most PCs and HDTVs use 709 gamut
• Majority of next generation content
uses Bt.2020 gamut
• 2015 UHDTVs are ~85% Bt.2020

11. 11
Bt 2020 content
displayed unmodified
on 709 display
Bt 2020 content
gamut-mapped for
709 display
We must perform gamut mapping

12. 12
Advantages of Wide Color
We can reproduce lifelike colors we
couldn’t before and create more
immersive experiences

13. 13
Dynamic Range
Simple definition:
• Ratio of largest to smallest
signal in a system

14. What is HDR (in this context)
Practically speaking:
 Content with a wider range of brightness and color
 Requires new monitors to experience HDR content
– Legacy content: 100 nit peak brightness, 709 gamut
– HDR content: 10,000 nit peak brightness, 2020 gamut
HDR is an ambiguous term
 There are several industry specs defining various flavors of HDR

15. 15
(new) HDR: what it is not
“HDR Photography”
2005-era HDR rendering/gaming
 Such as Half-Life2: Lost Coast demo
Both of these techniques generate images designed to be shown on an SDR monitor

16. 16
Let’s talk about light and humans…

17. Terminology
Luminance
 Quantitative measurement of amount of light passing through an area
 Can be unequivocally measured by instruments
 Linearly proportional to # of photons
Brightness
 Subjective human perception of luminance
 Varies wildly based on ambient conditions and from human to human
 Non-linearly proportional to # of photons

18. 18
Measuring Luminance
Nit (Candela/m2)
 Approximately equal to the amount of light from a candle dispersed over a
square meter

19. 19
Object Approximate Luminance (nits)
Sun 1,600,000,000
Arc lamp 150,000,000
Maximum visual tolerance 50,000
Cloud (sunny day) 35,000
2016 UHDTV 800-1000
Typical computer screen 100-300
White paper under lamp 50
Night sky (legacy) 0.001
Threshold of vision 0.000003

20. 40
nits
2,000 nits
500,000
nits
200,000
nits

21. 21

22. 22

23. 23

24. 24
TL;DR
Standard Dynamic Range:
 De facto brightness range of current content and displays
High Dynamic Range:
 Substantially brighter next-generation content and displays

25. 25
Standard Dynamic Range
For the past 80 years, video has been graded to appear properly on a 100 nit
display
However, no adjustments are made to comprehend displays of differing
luminance
– 30 nit laptops in low power mode
– 600 nit HDTVs in Vivid mode
Similarly, no adjustments to the content are made when you surf the web and
play games, switching from phones to tablets to PCs.
This is wrong, but has been good enough

26. 26
Disambiguation: HDR Photography
Multiple exposures from different times combined off-
line to create a single SDR image which has different
exposure levels for different areas of the picture
Not what we’re talking about today

27. 27
HDR Video
 Single exposure captures a wide range of luminance at a
single instant in time
 Intended to be displayed on an HDR display

28. 28
Things to ponder
With color, many real-world hues can be exactly reproduced on screens
Almost every real-world situation has objects at >100 nits
So the real world is HDR, and every SDR picture you take involves HDR->SDR
conversion
A 100-nit object on the screen almost never corresponds to a 100-nit object in
the real world

29. 29
Multiple ranges of HDR
0
nits
10,000
nits
ContainerCapture
15,000
nits
Movie DisplayContainerCapture Movie

30. 30
HDR Conversions
Capture Movie HDR Display
Mastering
Performed
by studio
creatives
Handled by
player
Handled
by
UHDTV
HDR->HDR
SDR Display

31. 31
HDR Content + SDR Display =
Bad
Experience
SDR Content + SDR Display = SDR Experience
SDR Content + HDR Display = SDR Experience
HDR Content +
HDR->SDR
Tone Mapping
SDR Display =
SDR
Experience
HDR Content + HDR Display = HDR Experience

32. 32
Real World
3,000
nits
300,000
nits

33. 33
Mastered for SDR
Coded
value=
0xFF
Coded
value=
0xFF
100
nits
100
nits

34. 34
Mastered for HDR
Coded
value=
0x23B Coded
value=
0x36C
200
nits
5,000
nits

35. Linear vs non-linear light
In the real world, luminance is determined by the number of photons
However, brightness (the human perception of luminance) is non-linearly
proportional to number of photons

36. Code Words
7
6
5
4
3
2
1
0
36
Directly storing luminance is inefficient
To prevent banding using SDR, you would need
to use 13-14 bits to code a contemporary 100-
nit signal
Luminance(linearscale)
Just noticeable difference

37. Luminance
Linear Light
Perceptually
non-uniform
Luma
Non-Linear Light
Perceptually
Uniform
0
1
0 1
To efficiently code video signals, we apply a non-linear transform function so
that we can code perceptually uniform brightness intervals

38. 38
Problems
Although gamma is a reasonable approximation of human perception in the
SDR (0-100 nit) range…
Gamma is not a good match for human perception in the 0-10,000 nit HDR
If you use gamma for a 10,000 nit signal, you need to use two extra bits/sample
to eliminate banding

39. 39
SMPTE 2084: HDR Electro-Optical Transfer Function (EOTF)
0
1
0 1
Luminance
Perceptually Uniform Video Signal
Gamma
EOTF

40. Blending
On computers, we usually blend colors in non-linear space
 Blended color= 0.5*(A+B)
This is fast and easy, but wrong because:
 Brightness A is really Luminance A’=A2.2
 Blended color ≠ 0.5*( A + B)
Correct answer:
 Blended color = 0.5(A’+B’) -> (0.5*( A2.2 + B2.2)) 1/2.2

41. Synthetic Case: Blending red and green
Non-linear
Linear
WRONG
RIGHT!

42. 42

43. Scaling
The same math applies not just to blending, but spatial scaling operations as well
 Scaling involves blending pixels together
Scaling in non-linear space will generate errors

44. 44
Advantages of HDR
HDR creates much more lifelike experiences
• “Like looking out a window”
• “Like you’re really there”
HDR done right is clearly distinguishable from existing content and displays

45. 45
HDR Usage Models
Movies
Gaming
Photography
VR

46. 46
Summary
HDR + WCG gives us powerful new tools to create visual experiences that are
clearly visible to the average viewer
You can watch HDR+WCG movies right now
Making this all work requires lots of changes to the production pipeline and the
products used to display it

47. 47
Call to Action
Make more HDR content and build more systems capable of playing HDR
Make sure you have a really compelling HDR experience before calling it HDR
Upcoming Intel products have cool HDR features…

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