Hable John Uncharted2 Hdr Lighting

Uncharted 2: HDR LightingJohn HableNaughty Dog

AgendaGamma/Linear-Space LightingFilmic TonemappingSSAORendering Architecture/How it all fits together.

Skeletons in the ClosetUsed to work for EA Black Box (Vancouver)‏

Also used to work for EA Los Angeles

GammaMostly solved in Film Industry after lots of kicking and screaming

Never heard about it in college

George Borshukov taught it to me back at EA

Issue is getting more traction now

Eugene d’Eon’s chapter in GPU Gems 3DemoWhat is halfway between white and black

Suppose we show alternating light/dark lines.

If we squint, we get half the linear intensity.DemoTest image with 4 rectangles.

Real image of a computer screen shot from my camera.DemoAlternating lines of black and white (0 and 255).DemoSo if the left and right are alternating lines of 0 and 255, then what color is the rectangle with the blue dot?DemoCommon wrong answer: 127/128.

That’s the box on the top.128

Color RampYou have seen this before.0127255187

Gamma Lines255F(x) = pow(x,2.2)‏1871270

What is GammaGamma of 0.45, 1, 2.2

Our monitors are the red oneWe all love mink...F(x) = xWe all love mink...F(x) = pow(x,0.45) note: .45 ~= 1/2.2‏We all love mink...F(x) = pow(x,2.2)‏What is GammaGet to know these curves…What is GammaBack and forth between curves.2.22.2.45.45

How bad is it?Your monitor has a gamma of about 2.2

So if you output the left image to the framebuffer, it will actually look like the one right.2.2

Let’s build a Camera…A linear camera.ActualLightMonitorOutput1.02.2HardDrive

Let’s build a Camera…Any consumer camera.ActualLightMonitorOutput.452.2HardDrive

How to fix this?Your screen displays a gamma of 2.2

This is stored on your hard drive.

You never see this image, but it’s on your hard drive.2.2

What is GammaCurves again.What is GammaQ) Why not just store as linear?A) Our eyes perceive more data in the blacks.

How bad is it?Suppose we look at the 0-63 range.

What if displays were linear?GammaGamma of 2.2 gives us more dark colors.How bad is it?If displays were linear:

1 would equal our current value of 20

Darkest Values:Ramp AgainSee any banding in the whites? 3D GraphicsIf your game is not gamma correct, it looks like the image on the left..

Note: we’re talking about “correct”, not “good”3D GraphicsHere's what is going on.ScreenHardDriveLighting

3D GraphicsAccount for gamma when reading textures

color = pow( tex2D( Sampler, Uv ), 2.2 )‏

Account for gamma on color output

finalcolor = pow( color, 1/2.2 )‏3D GraphicsHere's what is going on.MonitorAdjustHardDriveLightingShaderCorrectGamma

3D GraphicsComparison again...3D GraphicsThe Wrong Shader?Spec = CalSpec();Diff = tex2D( Sampler, UV );Color = Diff * max( 0, dot( N, L ) ) + Spec;return Color;

3D GraphicsThe Right Shader?Spec = CalSpec();Diff = pow( tex2D( Sampler, UV ), 2.2 );Color = Diff * max( 0, dot( N, L ) ) + Spec;return pow( Color, 1/2.2);

3D GraphicsBut, there is hardware to do this for us.

Hardware does sampling for free

D3DRS_SRGBWRITEENABLE3D GraphicsWith those states we can remove the pow functions.Spec = CalSpec();Diff = tex2D( Sampler, UV );Color = Diff * max( 0, dot( N, L ) ) + Spec;return Color;

3D GraphicsWhat does the real world look like?

Notice the harsh line.3D GraphicsAnother ExampleFAQsQ1) But I like the soft falloff!A1) Don’t be so sure.

FAQsIt looks like the one on top before the monitor’s 2.2Harsh FalloffDevastating.Harsh FalloffDevastating.Harsh FalloffDevastating.Which Maps?Which maps should be Linear-Space vs Gamma-Space?

Use sRGB hardware or pow(2.2) on read

Don’t use sRGB or pow(2.2) on read

128 = 0.5Which Maps?Diffuse Map

Definitely LinearWhich Maps?Specular?

Uncharted 2 had them as Linear

Artists have trouble tweaking them to look right

Probably should be in GammaWhich Maps?Ambient Occlusion

Technically, it’s a mathematical value like a normal map.

But artists tweak them a lot and bake extra lighting into them.

Probably should be GammaExercise for the ReaderGamma 2.2 != sRGB != Xenon PWL

Xenon PWL: Piecewise linear gammaXenon GotchasXbox 360 Gamma Curve is wonky

Way too bright at the low end.

HDR the Bungie Way, Chris Tchou

Post Processing in The Orange Box, Alex Vlachos

Output curve is extra contrasty

Henry LaBounta was going to talk about it.

Try hooking up your Xenon to a waveform monitor and display a test pattern. Prepare to be mortified.

Both factors counteract each otherLinear-Space Lighting: Conclusion“Drake! You must believe in linear-space lighting!”

Filmic TonemappingLet's talk about the magic of the human eye.Filmic TonemappingReal example from my apartment.

My eye somehow adjusts...Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingAdaptiveness of human eye.Filmic TonemappingOne moreFilmic TonemappingOne moreGammaLet’s take an HDR image

Note: 1 F-Stop is a power of two

So 4 F-stops is 2^4=16x difference in intensityGammaExposure: -4GammaExposure: -2GammaExposure: 0GammaExposure: 2GammaExposure: 4Now what?We actually need 8 stops

Re-tweaking exposure won't helpGammaThis is what Photography people call tonemapping.

The one we’ll use is globalPoint of ConfusionTwo problems to solve.

Dynamic Range in different shots

Hable John Uncharted2 Hdr Lighting

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Hable John Uncharted2 Hdr Lighting