Filmic Tonemapping for Real-time Rendering - Siggraph 2010 Color Course

SIGGRAPH 2010
Filmic Tonemapping
for Real-time Rendering
Haarm-Pieter Duiker
Duiker Research
hpd@duikerresearch.com

Filmic Tonemapping Overview
• History of Color in Games
• Scene-referred and Output-referred data
• Cineon Log
• What a filmic curve looks like
• Authoring a filmic curve
• Further work

SIGGRAPH 2010 Course: Color Enhancement and Rendering in Film and Game ProductionSIGGRAPH 2010 Course: Color Enhancement and Rendering in Film and Game Production 4

SIGGRAPH 2010 Course: Color Enhancement and Rendering in Film and Game ProductionSIGGRAPH 2010 Course: Color Enhancement and Rendering in Film and Game Production
HDR data in modern hardware
• What problems do modern hardware capabilities bring
with them?
– Working with HDR data implies Linear color math
– Linear data is displayed on non-linear devices
• monitors
• TV screens
12

Review of different color spaces
• Some (relatively) new terms
– Scene-referred
– Output-referred
– What? Why does this matter now?
• Two main color spaces
– Scene-referred Linear
– Output-referred sRGB
13

Two phase model of color rendering
• Render / Capture linear data
• Correct for the display’s characteristics
– Get the display to render the intensities of the ‘scene-
referred’ data as closely as possible to the original scene
16

What does Linear data “look” like?
17

SIGGRAPH 2010 Course: Color Enhancement and Rendering in Film and Game Production
• High contrast
• The dynamic range viewable on screen is small
• Integer formats can only represent a fixed dynamic
range
SIGGRAPH 2010 Course: Color Enhancement and Rendering in Film and Game Production
Issues with Scene-referred Linear data
23

Can we do better than sRGB?
• How do we make a scene-referred linear render
look like film?
• Can we add some artistic control to the proces?
– What if we want to make our render look like a film stock
that doesn’t exist?
25

Cineon Log - a new (old) color space
• Used in visual effects since circa 1993
• Important properties
– Pixel values correspond to negative density
• lg = (log10(ln/linReference)/ld*logGamma + logReference)/1023.f
• log Density ~= log10(Intensity) ~= Exposure
– HDR data in an LDR bit depth
• Values greater than 1 map to values less than 1
– Values close to 0 get a lot bits
29

Visualizing color spaces
30

Filmic Tonemapping - Four stages
• Render / Capture linear data
• Convert from Scene-referred Linear to Log
– Match the look of a negative film stock here
• Apply a “filmic” tonemap to match a print film stock
• Correct for the display’s characteristics
35

What does a “filmic” curve look like?
• Let’s look at some curves. Notice
– Toe
– Shoulder
– Channel separation
– “Linear” range
36

A “filmic” curve looks like - Kodak
37

A “filmic” curve looks like - Color Sym.
38

A “filmic” curve look like - Sony Anim.
39

A “filmic” curve looks like - EA / Naughty
40

Authoring a LUT - Process breakdown
• Screenshot from game
• Convert to Cineon Log
• Treat in Photoshop / Nuke / Grading suite of choice
– Make sure it’s a non-destructive edit (use layers)
– Or embed an identity lut
• Apply treatment to identity lut image
– Can be 1d or 3d
41

Screenshot from game
• Can we use Uncharted here?
52

Optimized implementation
• Three steps of color processing is too expensive
• Analytical approximations
– Jim Hejl and Richard Burgess-Dawson at EA
– John Hable at Naughty Dog
54

Analytical Approximations
• Linear all the way to sRGB-corrected
– Requires fitting parameters to authored lut
• Different approximations
55

Approximation 1
56
float4 ps_main( float2 texCoord : TEXCOORD0 ) : COLOR
{
float3 texColor = tex2D(Texture0, texCoord );
float3 x = max(0,texColor-0.004);
float3 retColor = (x*(6.2*x+.5))/(x*(6.2*x+1.7)+0.06);
return float4(retColor,1);
}

Approximation 2
57
float A = 0.15; float B = 0.50; float C = 0.10;
float D = 0.20; float E = 0.02; float F = 0.30; float W = 11.2;
float3 Uncharted2Tonemap(float3 x) { return ((x*(A*x+C*B)+D*E)/(x*(A*x+B)+D*F))-E/F; }
float4 ps_main( float2 texCoord : TEXCOORD0 ) : COLOR
{
float3 texColor = tex2D(Texture0, texCoord );
float ExposureBias = 2.0f;
float3 curr = ExposureBias*Uncharted2Tonemap(texColor);
float3 whiteScale = 1.0f/Uncharted2Tonemap(W);
float3 color = curr*whiteScale;

Is a 1d Filmic tonemap good enough?
• Effects not accounted for by a 1d lut
– Color cross-talk
– Saturation
– Gamut-mapping
58

Emulating an actual film stock
• Authoring a lut can be artistic or emulation driven
– Is emulation what your game needs?
– You can combine the two
59

Thanks
• Naty Hoffman
• John Hable
• Jim Hejl
• Kim Libreri
• George Borshukov
• Course contributors
60

Filmic Tonemapping for Real-time Rendering - Siggraph 2010 Color Course

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