Game Engine Gems 2

 45

3

SimulationofNight‐Visionand

InfraredSensors

Frank Kane

Sundog Software, LLC

Many action games simulate infrared (IR) and night-vision goggles (NVG) by

simply making the scene monochromatic, swapping out a few textures, and turn-

ing up the light sources. We can do better. Rigorous simulations of IR and NVG

sensors have been developed for military training and simulation applications,

and we can apply their lessons to game engines. The main differences between

visible, IR, and near-IR wavelengths are easily modeled. Sensors may also in-

clude effects such as light blooms, reduced contrast, blurring, atmospheric trans-

mittance, and reduced resolution that we can also simulate, adding to the realism.

3.1ThePhysicsoftheInfrared

The world of the infrared is a very different place from the world of visible

light—you’re not just seeing reflected sunlight, you’re seeing how objects radiate

heat. Accurately representing an IR scene requires understanding some basic

thermodynamics.

Fortunately, the bit we need isn’t very complicated—we can get by with just

an understanding of the Stefan-Boltzmann law. It tells us that the black body ra-

diation

*

j

of an object is given by

*4

j εσT



.

Here, T is the absolute temperature of the object (in Kelvins),



is the thermal

emissivity of the material, and



is the Stefan-Boltzmann constant,

8

5.6704 10





124

Js m K



 

. If the ambient temperature and temperature of the objects in your

46

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Figure

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dd additiona

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materials an

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epurpose th

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aterials

the tem-

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ke ideal

ns.

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in terms

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/or tex-

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. (Image

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s

3.1ThePhysicsoftheInfrared 47

Material Emissivity Material Emissivity

Aluminum 0.20 Paint 0.84 (white)–0.99 (black)

Asphalt 0.95 Paper 0.95

Cast iron 0.70–0.90 Plastic 0.95

Clay 0.95 Rusted iron 0.60–0.90

Cloth 0.95 Sand 0.90

Glass 0.85 Snow 0.90

Granite 0.90 Soil 0.90–0.98

Grass 0.98 Steel 0.80–0.90 (cold-rolled), 0.25 (polished)

Gravel 0.95 Tin 0.10–0.30

Human skin 0.95 Water 0.93

Ice 0.98 Wood 0.90–0.95

Table 3.1. Emissivity of common materials.

light textures of your objects as detail for the thermal information. There is a

range of about 0.15 in the emissivity between white and black objects; light col-

ors reflect more heat, and dark colors absorb it. Your fragment shader may con-

vert the RGB values of the visible-light textures to monochromatic luminance

values and perturb the final emissivity of the fragment accordingly. Listing 3.1

illustrates a snippet of a fragment shader that might approximate the thermal ra-

diation of a fragment given its visible color and knowledge of its underlying ma-

terial’s emissivity and temperature. This is a valid approach only for objects that

do not emit their own heat; for these objects, emissivities and temperatures

should be encoded directly in specialized IR textures, rather than blending the

visible-light texture with vertex-based thermal properties.

uniform sampler2D visibleTexture;

uniform sampler2D thermalTexture;

uniform float level;

uniform float gain;

uniform float stefanBoltzmannConstant;

uniform float emissivityBlendFactor;