/**
 * Minimal PNG decoder — zero external dependencies (only node's built-in
 * `zlib.inflateSync`). We need it so the pattern-graph can read a drawn image
 * (a histogram, a curve, a filled band) and turn it into a signal/corridor.
 *
 * Supports what real image exports actually produce: 8-bit (and 16-bit,
 * high-byte) grayscale/RGB/gray+alpha/RGBA, 8-bit palette (with tRNS alpha),
 * non-interlaced. Sub-byte depths and Adam7 interlace throw a clear "re-export"
 * error rather than decoding wrong. Output is a flat RGBA byte grid.
 */
export interface DecodedImage {
    readonly width: number;
    readonly height: number;
    /** Row-major RGBA, 4 bytes per pixel: `rgba[(y*width + x)*4 + c]`. */
    readonly rgba: Uint8Array;
}
/** Decode a PNG buffer into an RGBA grid. Throws on anything it can't read exactly. */
export declare function decodePng(buf: Uint8Array): DecodedImage;
/** Perceptual luminance 0..255 of an RGB triple (Rec. 601). */
export declare function luminance(r: number, g: number, b: number): number;
/** Whether the PNG signature is present — lets callers branch PNG vs SVG on `src`. */
export declare function isPng(buf: Uint8Array): boolean;
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