/**
 * Minimal PNG decoder for PDF image embedding.
 *
 * Extracts raw RGB pixel data from a PNG file. Handles:
 * - Color types: RGB (2), RGBA (6), Grayscale (0), Grayscale+Alpha (4), Palette (3)
 * - Bit depth: 8 (most common)
 * - Interlacing: non-interlaced only (Adam7 interlacing is not supported)
 * - All 5 PNG filter types (None, Sub, Up, Average, Paeth)
 *
 * For RGBA images, produces separate RGB pixels and an alpha mask (for PDF SMask).
 */
export interface DecodedPng {
    width: number;
    height: number;
    /** Raw RGB pixel data (3 bytes per pixel, row-major) */
    pixels: Uint8Array;
    /** Alpha channel (1 byte per pixel) — null if image is fully opaque */
    alpha: Uint8Array | null;
    /** Bits per component (always 8 after decoding) */
    bitsPerComponent: number;
}
/**
 * Decode a PNG file to raw RGB pixels for PDF embedding.
 * @throws on invalid or unsupported PNG data
 */
export declare function decodePng(data: Uint8Array): DecodedPng;