clarifying high dynamic range (hdr)€¦ · 15/10/2015 · clarifying high dynamic range (hdr) 4...

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SMPTE Monthly Education Webcast Series: Clarifying High Dynamic Range (HDR)

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Clarifying High Dynamic Range (HDR)

PART OF SMPTE’S MONTHLY EDUCATION SERIES

Sponsored by:

SMPTE Educational Webcast Sponsors

Thank you to our sponsors for their generous support of SMPTE and SMPTE’s Monthly Webcasts:

2© 2015 • Powered by SMPTE® Professional Development Academy • www.smpte.org



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SMPTE Monthly Education Webcast Series

Series of monthly 1-hour online, interactive webcasts covering a variety of technical topics

Free professional development benefit for SMPTE members

Sessions are recorded for member viewing convenience.


• Views and opinions expressed during this SMPTE Webcast are those of the presenter(s) and do not necessarily reflect those of SMPTE or SMPTE Members.

• This webcast is presented for informational purposes only. Any reference to specific products or services do not represent promotion, recommendation, or endorsement by SMPTE

© 2015 • Powered by SMPTE® Professional Development Academy • www.smpte.org 4



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Today’s Guest Speaker


Joseph SlomkaVice President and

Principal Color Scientist

FotoKem

Your Host

Joel E. WelchDirector of Education

SMPTE




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Introduction

This presentation will go over 3 main HDR topics

Effects of HDR display on the perception of resolution and depth

Experiences in support grading a HDR theatrical and a HDR video

How HDR can affect the artistic process


What is HDR

HDR is a technology that allows more more dynamic range than current displays. It allows for uncrushed blacks and unclipped whites




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Introduction

This is going to cover captured motion pictures

Much of this will apply, but differently, to Computer Graphics and VFX


Benefits of HDR

Acquisition• Captures a more complete version of the scene

• Display• Reproduces greater detail

• More natural image appearance*

• The ability to have greater local contrast

• The ability to have greater overall contrast

• Increased perception of color




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Goals

Connect the technical, scientific and artistic


A little about light



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Stops

Stops are a way of describing an amount of light

One stop represent a doubling of light

• Increasing one stop doubles the amount of light

• Decreasing one stop halves the amount of light

They have been used in photography because relevance to the process and have been adopted by digital cinematography

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stops = log2(linear_ light)© 2015 • Powered by SMPTE® Professional Development Academy • www.smpte.org

How Much DR is HDR?

Acquisition

Display




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How Much DR is HDR?

Acquisition

• Film • Greater than 14 stops (Kodak 5219)

• A good starting point for acquisition

Display• DCI DCP

• Around 10 stops at rated contrast ratio(2000:1, 1200:1)

• More than that is where HDR begins


Human Perception and Dynamic range TYING TOGETHER HDR, UHD, AND HFR



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HDR , 4K,HFR: How They Fit Together

Higher dynamic range allows for more image contrast

The higher contrast allows for greater perception of detail

Higher luminance increases the perception of flicker

Higher frame-rate reduces flicker

Each of these technologies increases the value of the other creating better pixels


Visual Limits

Dynamic range of vision

23-43 stops

Simultaneous dynamic range

10-14 stops




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Contrast, Resolution and HDR

Ability to see contrast dependent on brightness

Higher contrast between pixels allows for greater perception of detail


HDR and Resolution

Contrast sensitivity function

Contrast is a key part of identifying detail




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Contrast and Resolution

Contrast and Resolution

Contrast as Resolution



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Contrast Sensitivity Function

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Attribution By: Star Whitt-FrousiakisLocated at: commons.wikimedia.org/wiki/File:Contrast_Sensitivity_vs._Spacial_Frequency.png

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Contrast Sensitivity Changes With Brightness

You become more sensitive to high frequency detail in brighter light

Another way to say it

• The brighter an image is the less contrast you need to see detail

• From 90-900-9000 cd/m^2 there is a significant change

• http://webvision.med.utah.edu/imageswv/KallSpat24.jpg


http://webvision.med.utah.edu/imageswv/KallSpat24.jpg



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Contrast and Depth Perception

Stereo images are only part of seeing depth


Contrast and Depth



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Ways Depth is Perceived

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http://www.hitl.washington.edu/projects/knowledge_base/virtual-worlds/EVE/III.A.1.c.DepthCues.html

Accommodation

Convergence

Binocular Parallax

Monocular Movement Parallax

Retinal Size

Linear Perspective

Texture

Position

Aerial Perspective

Shades and Shadows


Ways Depth is Perceived

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Accommodation

Convergence

Binocular Parallax

Monocular Movement Parallax

Retinal Size

Linear Perspective

Texture• The closer we are to an object the more detail we can see of its surface texture. • Objects with smooth textures are usually interpreted being farther away. This is especially true if the surface

texture spans all the distance from near to far.

Position

Aerial Perspective

Shades and Shadows• The location of a light source and see objects casting shadows on other objects• bright objects seem to be closer to the observer than dark ones.






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Flicker and Luminance

Flicker can be described with temporal sensitivity

As average luminance increases so does flicker sensitivity

Color is adaptive, flicker is not


QuestionsASK AWAY

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HDR and the artistic process

A Different Look

How can it help the story?

How can it hurt?




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Trickshot

Gale Tattersall - Director of Photography

Curtis Clark ASC– HDR and ACES technical consultant

Senior Colorist – John Daro


Trickshot

Designed to show off the C300MKII

Ground up HDR

• Onset HDR mastering

ACES 1.0

• Pre-release

NAB delivery




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Onset with HDR

Trick Shot

Preproduction Canon monitor 400nit

• Available this month

Using Canon raw


SDR Grade

An experienced DP and Colorist leaves little chance for unnecessary drama




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Secret HDR Grade

Secret 2000 nit 4k prototype display with SMPTE 2084 encoding

Graded on the show floor using ACES 1.0 on the Mistica

Separate grade on selected shots

• Tradeshow goodness


Notes

HDR monitoring on set with 400 nit HDR display

HDR presentation and final grade on 2000 nit

Sense of depth

Texture




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San Andreas

Director of Photography – Steve Yedlin

Senior Colorist - Walter Volpatto

Dolby Technical Lead - Thaddeus Beier

Dolby Assistant Colorist -Rick Taylor


Feature Color Correction

San Andreas

Theatrical Master

Video Master 108 nits

Dolby Vision 4000 nits




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San Andreas

Acquired with ARRI Alexa

Using custom color science from Steve Yedlin.


Strong Vision

The photography was captured with a specific vision

The DCP grade was made in a way similar to a traditional film grade

• Very few windows, highlights were allowed to blow out if that is how they fell on the rendering




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HDR Color Setup

The look for the 2d version had a directed artistic vision

Preserving that look and mapping it to HDR was central to the design process

The HDR lookup table was set so that everything below diffuse white was left untouched.

Above diffuse white the lut was stretched to show additional highlight detail, then preserving the original roll off

No access to an HDR display before the session


HDR Color Setup Results

The DCP material was graded in a way that did not constrain the dynamic range and was ideal for HDR

Many scenes were completely unchanged

Many scenes were mostly unchanged




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Unexpected Results and Notes

Technically the look of the film was largely preserved

• Most of a frame is composed below diffuse white

The notes from the grading colorist are nuanced


Consistent Pixels : Inconsistent Feel

Ideally the state of adaptation would remain constant over the picture with the highlights being perceived as specular detail

• This didn’t hold up everywhere

Vistas, cityscapes, outdoors, fire and machines were amazing

Scene with sufficient highlight caused faces to feel dim

• Vision adjusted to specular light, not nominal

• This was true even with just 1 more stop of range

Even a small amount of highlight in a scene caused the issue

Technically correct, artistically incorrect




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Inconsistent Look

Unwanted details

• Lights become directional

• New light shapes


Colorist Notes

After the project was delivered 4 different paths were identified:

1. Start from scratch• No tone map or trims

2. Stretch the signal• Extend the contrast, blacker blacks, whiter whites

3. Raise exposure• Make everything brighter

4. Combination • Make it brighter with limited additional highlights




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My Notes

It all makes sense once you see it

The way we see and the way we create are not the same

Cinematography is concerned about ratios

• We should be as well

Different results

• Trickshot vs San Andreas


QuestionsASK AWAY




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Problems in HDR

Exposure and Dynamic Range

Exposure- Brightness or darkness of a scene

Dynamic range- the range of available light




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No Agreed Upon Image Parameters

There is no standard for black, white or grey in HDR

This is a problem


This is One of the Two Big Headaches

A lot of high tech solutions are being developed to deal with this issue

No desire to limit all masters to the smallest dynamic range

No display reaches the highest value of 10,000

Capture becomes extremely challenging




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Wide Variety in Display Performance

Display peak white values vary greatly

• 400-4000cd/m^2

Black levels as well

• LCD to OLED blacks


Current TV’s Have a Lot of Variability

Current home TV’s have a lot of variability

Target master luminance is typically 100 nits

Homes can have 250-400 nits

However dynamic range is fixed




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Won’t someone think of the Children Editors Advertisers?

If exposure values vary to much editorial becomes impossible

Selling ads also becomes difficult viewing an SDR ad in HDR content could look very different


Picking a Point, nit Picking

Cinematographers already solved this issue

• Build the image around people

• Dynamic range built around that




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Good HDR comes from artists

Although the cameras capture HDR it needs artistic direction

Post ‘conversion’ of HDR is more difficult than starting with HDR


QuestionsASK AWAY

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The Wild West of HDR

Several Specifications, But No Standards

Competing specifications mean no standards




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Competing Formats

BBC

Technicolor

Dolby

Phillips


No Perfect Answer

Each solution comes from a specific viewpoint and solves specific issues

The rooms I am in mention Dolby and BBC as the main proposals

• I may just be in the wrong rooms




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BBC

Attempts to be compatible with existing monitors, TV and distribution

Keeps the midtone and shadows the same as rec709

Adjusts highlights for the extra dynamic range

No-metadata


Dolby

A new approach not backwards compatible

Based on decades of vision research

Fully designed end to end

Provide SDR compatibility mode

PQ encoding

Uses metadata to provide display mapping




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Technicolor

Encoding curve with parameters

Uses metadata

Supports a variety of encoding scenarios


Philips

Parameter based HDR

Uses HDR grade as starting point

Tone-mapping and metadata produce the Standard Dynamic range




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Blu-ray Also Complicates This

As part of the Blu-ray HDR specification there is a limit to an APL of 400 nits


Q&A – Verbal Questions Take Priority!


Joel E. Welch

Joseph SlomkaVice President and

Principal Color Scientist

FotoKem



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SMPTE Education Webcast Series Sponsors

Thank you to our sponsors for their generous support of SMPTE and SMPTE’s Monthly Webcasts:


clarifying high dynamic range (hdr)€¦ · 15/10/2015 · clarifying high dynamic range (hdr) 4...

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