/**
 * The colour as it may be written into a style attribute, or `undefined`. A hex colour, `rgb()`, `rgba()`, `hsl()`,
 * `hsla()`, a colour name or `var(--name)` is drawn; anything else is ignored, so nothing from a form or an address
 * can end the attribute or add a rule.
 * @example
 * ```ts
 * import { safeColour } from "@johnmorrisdotca/kyogijo-stadiums";
 * console.log(safeColour("#1f5fa8"), safeColour("red;fill:url(x)"));
 * // #1f5fa8 undefined
 * ```
 */
export declare function safeColour(value: unknown): string | undefined;
/** The red, green and blue of a colour, when it can be read without a browser (a hex colour, `rgb()` or a common name). */
export declare function rgbOf(value: string | undefined): [number, number, number] | undefined;
/** The relative luminance of a colour, 0 (black) to 1 (white). */
export declare function luminance(rgb: [number, number, number]): number;
/** White or near-black, whichever reads better on the colour. White when the colour cannot be read. */
export declare function inkOn(color: string | undefined): string;
/**
 * A picture's address as it may be written into an image's `href`, or `undefined` (what `safeLogo` checks after it has looked for an emblem's id). An `https:` or `http:` address, a
 * relative path, an image `data:` address, or an SVG document as text (written as an image, which cannot run scripts).
 * @example
 * ```ts
 * import { safePicture } from "@johnmorrisdotca/kyogijo-stadiums";
 * console.log(safePicture("https://example.com/gulls.svg"), safePicture("javascript:alert(1)"));
 * // https://example.com/gulls.svg undefined
 * ```
 */
export declare function safePicture(value: unknown): string | undefined;