/**
 * Image header parsing: format sniffing and dimensions, with no decompression.
 *
 * Kept apart from the PNG codec so input validation, which runs on every request that carries an
 * image, loads only this and never the pixel decoder. Reading headers only is also what lets a
 * pixel ceiling stop a decompression bomb before anything is inflated.
 */
export type SniffedImageFormat = 'png' | 'jpeg' | 'gif' | 'webp' | 'avif' | 'bmp';
/** An image format recognised from its first bytes. */
export interface SniffedImage {
    /** The format. */
    format: SniffedImageFormat;
    /** Its MIME type. */
    mimeType: string;
}
/** Image dimensions read from a header. */
export interface ImageDimensionsInfo {
    /** Width in pixels. */
    width: number;
    /** Height in pixels. */
    height: number;
}
export declare const PNG_SIGNATURE: number[];
/** Identifies an image from its first bytes, ignoring whatever the caller claimed it was. */
export declare function sniffImageType(bytes: Uint8Array): SniffedImage | undefined;
/**
 * Reads width and height from the header without decoding pixels.
 *
 * Returns `undefined` for a format it cannot measure, so a caller enforcing a pixel ceiling can
 * choose to refuse rather than decode blind.
 */
export declare function readImageDimensions(bytes: Uint8Array): ImageDimensionsInfo | undefined;
/** @internal Byte helpers shared with the PNG codec. */
export declare function startsWith(bytes: Uint8Array, signature: readonly number[]): boolean;
export declare function ascii(bytes: Uint8Array, offset: number, length: number): string;
export declare function readUint32BE(bytes: Uint8Array, offset: number): number;
export declare function readUint32LE(bytes: Uint8Array, offset: number): number;
export declare function readInt32LE(bytes: Uint8Array, offset: number): number;
export declare function readUint24LE(bytes: Uint8Array, offset: number): number;
export declare function readUint16BE(bytes: Uint8Array, offset: number): number;
export declare function readUint16LE(bytes: Uint8Array, offset: number): number;