/**
 * Calibration of the output pipeline, in linear scene luminance (1.0 = a white-looking surface at
 * exposure 1).
 *
 * `WHITE_POINT` is the luminance the pipeline prints as display white under AgX. Everything above it
 * is highlight headroom the tone curve rolls off, so a material meant to read as white is authored at
 * 1.0 rather than at whatever the sun happened to be set to.
 * `MID_GREY` is an 18% grey card — the metering target. Clamped auto-exposure drives the frame's key
 * luminance here, which is what makes one material read the same in a street at noon and a lamp-lit
 * room. There is one white point and one metering target; a second copy anywhere would make a grade
 * depend on which stage read it.
 */
export declare const WHITE_POINT = 1;
/** Linear scene luminance of an 18% grey card — the auto-exposure metering target. */
export declare const MID_GREY = 0.18;
/**
 * Pixels count toward metering up to this multiple of {@link WHITE_POINT}. A window or a sun disc sits
 * far above it and would otherwise pull the whole frame down to a silhouette.
 */
export declare const METERING_HIGHLIGHT_CEILING: number;
/** Bounds and adaptation policy for clamped auto-exposure. */
export interface AutoExposureConfig {
    /** Lowest exposure multiplier the meter may reach. Default 0.6 (0.7 stops down). */
    min?: number;
    /** Highest exposure multiplier the meter may reach. Default 2.5 (1.3 stops up). */
    max?: number;
    /** Seconds for the meter to cover ~63% of a gap to a new key luminance. Default 0.6. */
    adaptationSeconds?: number;
}
/**
 * Default clamped auto-exposure. The range is deliberately asymmetric: a bright street is already
 * readable after AgX's shoulder, while a lamp-lit interior is the case that crushes, so the meter may
 * lift 1.3 stops but only darken 0.7 — an artist's exposure survives.
 */
export declare const DEFAULT_AUTO_EXPOSURE: Readonly<Required<AutoExposureConfig>>;
/**
 * Exposure that places a frame whose key luminance is `keyLuminance` on {@link MID_GREY}, bounded by
 * the authored range. A dark interior asks for more than `max` and gets `max`; a blown-out exterior
 * asks for less than `min` and gets `min`, so the frame never runs away at either end.
 */
export declare function exposureForKey(keyLuminance: number, config?: AutoExposureConfig): number;
/**
 * Frame-rate independent blend of `current` toward `target`, exponential in time so a hitch does not
 * overshoot and a steady view settles. `deltaSeconds` may be 0..∞; a zero-length step keeps `current`.
 */
export declare function adaptExposure(current: number, target: number, deltaSeconds: number, adaptationSeconds?: number): number;
/**
 * Key luminance of a metered frame: the median of its samples, each clamped to
 * {@link METERING_HIGHLIGHT_CEILING}. A median rather than a mean because a bright sky, a window or a
 * lamp is a large minority of the frame: averaging those in drags an interior down to a silhouette,
 * where the median still reports the room.
 */
export declare function keyLuminanceFromSamples(samples: ArrayLike<number>): number;