threejs-exposure-color-grading

Exposure And Color Grading

Keep the photographed signal scene-linear until the final image chain. One declared owner controls each exposure group, tone map, and output conversion.

1. Lock the color contract

Name the scene-linear working primaries, radiance scale, alpha convention, and every producer that enters the photographed signal. Convert irradiance through the material/lighting model before metering radiance. Apply one shared physical or perceptual radiance scale to lights, environment, atmosphere, emissive materials, bloom sources, and optical effects.

Partition targets or views into exposure-control groups. A group may share GPU state only when its radiance basis, exposure policy, and reset history are identical; an automatic group also requires the same meter mask, key, and sample schedule. Assign exactly one exposure owner, one tone-map owner, and one output-conversion owner per group.

Complete when: every photographed input has one basis and scale, and every group names its members, exposure/tone-map/output owners, and state-sharing policy.

2. Choose the cheapest meter that meets the image requirement

Choose in dependency order:

1. fixed EV for a controlled or calibrated view;
2. a stratified grid or tile sampler for ordinary global auto exposure;
3. exact full-pixel hierarchical reduction when every pixel or exact mask must contribute;
4. a log-luminance pyramid only when another feature consumes its levels or spatial statistics;
5. a histogram only when percentile clipping fixes a demonstrated outlier or bimodal-lighting failure.

Tap resolved, pre-bloom HDR by default. This keeps temporal noise out of the meter and avoids bloom/exposure feedback. A different tap is an authored image policy with a regression fixture.

Read the color-pipeline reference when implementing sampled, exact, pyramid, or histogram metering; it contains the weighted-log equations, traffic model, and small-emitter failure tests.