/**
 * Colour maths for palette-legal editing.
 *
 * Pixel art lives or dies by palette discipline, and "nearest colour" in RGB
 * space is not the colour a human would pick — RGB distance weights green far
 * too heavily and ignores lightness. Everything here works in CIELAB with
 * CIE76 ΔE, which is close enough to perceptual for a ≤64-colour palette and
 * cheap enough to run per-pixel.
 */
export interface Rgb {
    r: number;
    g: number;
    b: number;
    a: number;
}
export interface Lab {
    l: number;
    a: number;
    b: number;
}
export declare function parseHex(hex: string): Rgb;
export declare function toHex({ r, g, b, a }: Rgb, includeAlpha?: boolean): string;
export declare function rgbToLab({ r, g, b }: Rgb): Lab;
/** CIE76 ΔE. Values below ~2.3 are indistinguishable to most viewers. */
export declare function deltaE(a: Lab, b: Lab): number;
export interface SnapResult {
    index: number;
    hex: string;
    distance: number;
}
/**
 * Nearest palette entry to `colour`, by ΔE.
 *
 * A fully transparent input snaps to itself: a palette has no entry for
 * "nothing", and picking the nearest opaque colour for it would paint over
 * holes the artist left on purpose.
 */
export declare function snapToPalette(colour: Rgb, palette: readonly string[]): SnapResult;
export interface HueShiftOptions {
    /** Positive lightens, negative darkens. Roughly one ramp step per 0.15. */
    amount: number;
    /** Degrees of hue rotation applied at full amount. */
    hueShiftDegrees?: number;
}
/** Rotate `h` toward `target` along the shorter arc, by at most `degrees`. */
export declare function rotateHueToward(h: number, target: number, degrees: number): number;
/**
 * Shade a colour the way a pixel artist does, not the way a brightness slider
 * does: shadows rotate toward blue and desaturate slightly, highlights rotate
 * toward yellow and saturate. Flat luminance ramps are the single most common
 * tell of machine-made pixel art.
 *
 * The rotation goes toward a target hue, not a fixed direction round the
 * wheel: a fixed "+N° for shadows" sends red shadows toward orange and yellow,
 * which is the opposite of what a red ramp needs.
 */
export declare function hueShiftShade(colour: Rgb, opts: HueShiftOptions): Rgb;
export interface Hsl {
    h: number;
    s: number;
    l: number;
}
export declare function rgbToHsl({ r, g, b }: Rgb): Hsl;
export declare function hslToRgb({ h, s, l }: Hsl): Omit<Rgb, "a">;
/**
 * Build a hue-shifted ramp of `steps` colours around a base colour.
 * The base sits at the ramp's midpoint so callers get equal shadow and light.
 */
export declare function buildRamp(base: Rgb, steps: number, spread?: number): string[];
/** Perceptual luminance, used by contrast and readability checks. */
export declare function luminance({ r, g, b }: Rgb): number;
export declare function contrastRatio(a: Rgb, b: Rgb): number;