Filmic Tonemapping - EA 2006

Filmic Tone Mapping
Haarm-Pieter Duiker – EALA
George Borshukov – WWVG
2006/10/27

History of Color In Video Games
• Progression of Game Graphics
– Galaga
– Super Mario
Jump forward a few years
– Bond
– Madden
– Need For Speed
– Gears of War

Copyright @1982 Namco Corp.

Copyright @1988 Nintendo of America Inc

Copyright @ 2003-2004 Electronic Arts Inc

HDR and Next-gen Hardware
• What problems do new hardware
capabilities bring with them?
– Working with HDR data implies Linear color
math and workflows
– So you need to…
• Linearize your textures on read
• Compensate for the characteristics of display
devices through Tone Mapping
• Choose a Tone Mapping algorithm

What Does Linear Data Look Like?
Copyright ©2004 Nvidia Corporation

• Issues
– Overly Contrasty
– The dynamic range viewable on screen is
relatively small
– Trying to work with this data in integer formats
will quickly lead to quantization artifacts

Contrast Range Covered by
Different Tone Mapping Options

A Filmic Approach to Tone Mapping
• A New Option for Games
• Core Idea: Two Stages
– 1 Transform Linear Data into a Logarithmic
color space
– 2. Apply LUT to Log data

A Filmic Approach to Tone Mapping
• Advantages
– Distributes Bits Evenly Across Dynamic
Range – Darks and Highlights
– Encodes Relevant Broad Dynamic Range
using Integer Format
– Plays Nicely with Modern Hardware
– Provides a Broader Range of Control for Art
Direction

Log Color – Background
• Human Visual System
– We think of Exposure in Log Terms
– Stops are powers of 2
• Film Measurements standard
– Density is a Log measure of Intensity
– Used for Print and Negative Measurements
• Cineon Compositing System
– Visual Effects interchange standard

Log Color – Background
Copyright © Kodak Corp.

Log Color – The Math
Linear to Log
c = (log10(ln/linReference)/ld*logGamma +
logReference)/1023.f;
- Conversion is handled easily by Cg and HLSL
- Could be sped up by converting to a 16 bit LUT

Log Color – The Math
Log to Linear
c = pow(10, (lg*1023.f–logReference)/
(ld*logGamma))*linReference;
- Conversion is handled easily by Cg and HLSL
- Could be sped up by converting to a 8 bit LUT
• There are a few constants in that equation.

Dynamic Range Coverage Comparison
• Log
– Dynamic Range covered by default parameters:
• 0.002 to ~67.5
– Bits per stop using for 8 bit Log with default
parameters:
• 17 8 bit code values ~ 4 bits
– Defaults can be adjust to cover less dynamic range
thereby allocating more bits per stop of dynamic
range

• Gamma
– Dynamic Range covered by Gamma/Exponent
Approach:
• 0 to 1
– Bits per stop using for 8 bit Gamma 2.2
• Average : 24.4
• Max is 69 8. Min is 1.7 = ~ 1 bit.
– Decreases for Darker values, where the human
visual system is most sensitive
– Lifts Black Level

An Exponential Ramp – Each Step = 1 Stop
- Will appear Linear to the Human Eye
- Large range above 1 not shown here

A Log Ramp – Each Step = 1 Stop
- Represents wide dynamic range consistently
- Needs a LUT to prepare for display

An Gamma Ramp - Each Step = 1 Stop
- Will appear Linear when displayed on a monitor
- Will show banding and quantization in the darks
- Clamps values above 1

Log Color – On Modern Hardware
• Allows HDR data to be stored in a LDR
integer format
• Color Correction can be done quickly in
this space
• Speculation: This might work equally well
on Xenon and PS3 hardware

Log Color – Possible Disadvantages
• Pow and Log calls may be expensive (?)
– Log is cheap. Pow is expensive.
– Can be sped up using LUTs
• Dynamic Range is fixed, not infinite.
– Highlights beyond a certain range will be clipped
– Darks beyond a certain range will be clipped
• Gamma approach not much better at representing dark
detail - ~1 bit
• Blending Operations expect Linear data

Filmic Tone Mapping
• Artistry after the Log Conversion
– Starting with Log color data gets you a long
way
– Simple Authoring pipeline
– 1d vs. 3d. LUTs
• Short story: Either approach can be used.

Filmic Tone Mapping
• What makes a LUT “Filmic”?
– Linear Middle Section
– “Shoulder” – Soft Compression of Highlights
– “Toe” – Soft Compression of Darks

Filmic Tone Mapping - Examples

Filmic Tone Mapping – Example

Tiger Demo
• Real time demo using Filmic Tonemapping

Thanks for Your Time
• Questions?

Filmic Tonemapping - EA 2006

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Editor's Notes