export declare const bytesToBase64: (bytes: Uint8Array) => string;
export declare const base64ToBytes: (base64: string) => Uint8Array;
export declare function bytesToDataUri(bytes: Uint8Array, mimeType: string): string;
/** Samples per pixel: gray, RGB, RGBA. Maps to PNG colour types 0 / 2 / 6. */
export type PngChannels = 1 | 3 | 4;
/**
 * Encode 8-bit samples as a PNG.
 *
 * `pixels` is tightly packed, `channels` samples per pixel, row-major, with no
 * row padding. Rows are Paeth-filtered and the IDAT is real deflate — an
 * earlier version emitted zlib *stored* blocks, which made output 77–231×
 * larger than necessary on real documents.
 */
export declare function encodePng(pixels: Uint8Array | Uint8ClampedArray, width: number, height: number, channels: PngChannels): Uint8Array;
/**
 * Prefix each row with PNG filter type 4 (Paeth) and filter it in place.
 * Paeth is a good all-round default: it costs one pass and beats unfiltered
 * rows on both photographic and flat-colour content.
 *
 * One iteration per SAMPLE, so the edges are peeled out and the interior runs
 * branch-free. Each peeled case follows from the predictor's definition:
 *
 *   y = 0, x <  channels   a=b=c=0  → 0
 *   y = 0, x >= channels   b=c=0    → a  (Sub)
 *   y > 0, x <  channels   a=c=0    → b  (Up)
 */
export declare function paethFilterRows(pixels: Uint8Array | Uint8ClampedArray, width: number, height: number, channels: number): Uint8Array;