Shader Story

Lighting Models : Lookup Tables (LUT)

Lookup Table (LUT) is a way to remap complex lighting outputs or color responses using precomputed textures.

Instead of recalculating light equations every frame, LUT store color or lighting relationships inside a texture, which the shader simply samples at runtime.

This technique is used for stylized rendering and color grading.

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Visual demo

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// Pseudo-code (Complete per-vertex and per-pixel implementations, with detailed comments, are available in the related Patreon post)
// Link: https://www.patreon.com/posts/shader-story-lut-142912145


// Input lighting color
inputColor = (r, g, b)

// Sample LUT per channel (1D lookup along X axis)
lutColor.r = sampleLUT(inputColor.r)
lutColor.g = sampleLUT(inputColor.g)
lutColor.b = sampleLUT(inputColor.b)

// Blend original lighting with LUT-mapped result
finalColor = lerp(
    inputColor,
    lutColor × inputColor,
    LutTransition
)

// Output color after LUT coloring
return finalColor

Complete per-vertex and per-pixel implementations, with detailed comments, are available on Patreon.

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Basic idea

A Lookup Table (LUT) acts as a color transformation map. Each lighting value (or color channel) is used as a coordinate to fetch precomputed color information from a texture.

This allows to fine-tune the lighting output. Without the actual lighting setup change it's possible to set the tone remapping to stylize the project visuals.

Typical workflow:

• Compute lighting normally (e.g., Blinn-Phong, Lambertian, etc.)
• Use lighting color or intensity as input to a LUT texture
• Sample LUT and blend results with the original lighting
• Adjust blending strength to control stylization

Image-Based Lighting Equation

C_output = lerp(C_in, T(C_in) × C_in, α)

Where:

Where:

• C_in - input lighting color
• T(C_in) - texture lookup from LUT
• α - LUT blending factor (transition control)

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🔗 Related Functions

Lerp • Dot • Saturate

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