@cantoo/upng

PNG / APNG encoder and decoder based on photopea/UPNG.js via @pdf-lib/upng (the library Hopding wired into pdf-lib in PR #361), vendored for @cantoo/pdf-lib.

Benefits vs original UPNG / @pdf-lib/upng

| | photopea/UPNG.js & @pdf-lib/upng | @cantoo/upng | | ----------- | ----------------------------------------------- | ------------------------------------------------------------------------------- | | Compression | pako | fflate | | Packaging | Separate npm package | Also shipped as @cantoo/pdf-lib/upng | | Source | One monolithic UPNG.js | Modular TypeScript (decode, encode, quantize, framize, filter, …) | | Encode | Full UPNG (quantize, framize, lossy cnum) | Same feature set, ported from photopea's current sources | | Types | @pdf-lib/upng ships .d.ts | Same public surface, types generated from the sources |

The encoder keeps photopea's KD-tree + k-means quantization, APNG framize, and lossy palette encode when cnum < number of colors.

API

import UPNG from '@cantoo/upng';

const img = UPNG.decode(/* ArrayBuffer */);
const rgba = UPNG.toRGBA8(img)[0]; // ArrayBuffer of RGBA8 pixels

const png = UPNG.encode([rgba], width, height, 0); // 0 = lossless / auto
const pngQ = UPNG.encode([rgba], width, height, 256); // quantize to ≤256 colors
const q = UPNG.quantize(rgba, 64);
const pngLL = UPNG.encodeLL([samples], width, height, 3, 1, 8);

UPNG.compress (also a named export) gives finer control over framing, palette and dithering:

// [onlyBlend, evenCrd, forbidPrev, minBits, forbidPlte, dither]
const nimg = UPNG.compress([rgba], width, height, 64, [
  false,
  false,
  false,
  0,
  false,
  true,
]);

Also available via @cantoo/pdf-lib/upng when pdf-lib is installed.