HDR Auto Exposure

Continuously meter scene luminance and adapt camera exposure entirely on the GPU. createHDRAutoExposureShaderPassPipeline uses a center-weighted logarithmic luminance pyramid, persistent exposure history, and independent brightening and darkening response speeds.

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At a Glance

Property	Value
Export	createHDRAutoExposureShaderPassPipeline
Backend	WebGPU
Render passes	Seven: extraction, four reductions, adaptation, and application
Persistent state	One GPU-owned exposure-history texture
Recommended input	Linear rgba16float scene color

Usage

import {ShaderPassRenderer} from '@luma.gl/engine';
import {
  createBloomShaderPassPipeline,
  createHDRAutoExposureShaderPassPipeline,
  toneMapping
} from '@luma.gl/effects';

const renderer = new ShaderPassRenderer(device, {
  colorFormat: 'rgba16float',
  shaderPasses: [
    createHDRAutoExposureShaderPassPipeline({meteringScale: 0.25, initialExposure: 1}),
    createBloomShaderPassPipeline({quality: 'high'}),
    toneMapping
  ]
});

renderer.renderToScreen({
  sourceTexture: hdrSceneTexture,
  uniforms: {
    hdrAutoExposureAdapt: {
      keyValue: 0.48,
      minimumExposure: 0.45,
      maximumExposure: 2.4,
      brightenSpeed: 1.6,
      darkenSpeed: 2.8,
      deltaTime: frameDeltaSeconds,
      enabled: 1
    }
  }
});

Parameters

Parameter	Default	Description
meteringScale	0.25	Initial luminance-target scale; smaller values are clamped to 0.25.
initialExposure	1	Value used to initialize or recreate persistent exposure history.
keyValue	0.48	Target middle-gray response used to derive scene exposure.
minimumExposure	0.45	Lower bound on the adapted exposure multiplier.
maximumExposure	2.4	Upper bound on the adapted exposure multiplier.
brightenSpeed	1.6	Adaptation rate when the image needs to become brighter.
darkenSpeed	2.8	Adaptation rate when the image needs to become darker.
deltaTime	0.016	Current frame duration in seconds; update this application-owned uniform every frame.

How It Works

1. Sample a 4-by-4 footprint and accumulate center-weighted logarithmic luminance.
2. Reduce four successively smaller floating-point pyramid levels.
3. Derive geometric-mean scene brightness without copying results back to the CPU.
4. Adapt and clamp the persistent exposure target with direction-specific response speeds.
5. Multiply the original HDR scene color by the current adapted exposure.

The pipeline can also expose a false-color luminance visualization through the application-stage debug uniform. Reset renderer history when a resize, camera cut, or scene replacement should discard the previous adaptation state.

Related Effects

• Bloom supports exposure-aware highlight thresholds and exposure-corrected temporal history.
• Tone Mapping converts the adapted HDR image into display-ready color.
• Temporal Antialiasing normally precedes exposure and bloom in the render stack.