Rapier JXL

Rapier's complete JPEG XL encoding system in 50,021 gzip bytes: lossless and lossy encoding, native precision, HDR, exact alpha, JPEG transcoding, optional WASM and parallel workers. JavaScript, zero runtime dependencies, offline. MIT license.

This is the complete worker used by Rapier. The separate core is 11,670 gzip bytes. Both can be embedded in one HTML file.

npm install rapier-jxl

Builds

| Build / import | Gzip bytes | Capabilities | | --- | ---: | --- | | Rapier worker · rapier-jxl/rapier/worker | 50,021 | Core + effort 1–9, optional WASM, Photo, JPEG transcoding and parallel lossless groups. | | Rapier module · rapier-jxl/rapier/min | 50,075 | The same system with an encoder factory and worker installer. | | Core · rapier-jxl/min | 11,670 | Lossless or lossy typed RGBA, native precision, HDR and exact alpha. | | Effort · rapier-jxl/effort/min | 30,013 | Core with lossless compression search, efforts 1–9. | | WASM · rapier-jxl/wasm/min | 36,336 | Effort with inlined WASM and JavaScript fallback. | | Photo · rapier-jxl/photo/min | 15,837 | Lossy photographs from RGBA pixels. | | JPEG · rapier-jxl/jpeg/min | 13,882 | Existing JPEGs, preserving admitted coefficients and orientation. | | Metadata · rapier-jxl/metadata/min | 2,560 | Attach, replace or remove caller-supplied Exif/XMP. |

Each size measures a complete standalone file at gzip level 9. Readable imports such as rapier-jxl/rapier share dependencies when bundled together; separate minified files each include theirs. Optional JPEG and Photo ANS builds, combined sizes and file hashes are listed in Entry points and embedding.

Used by Rapier: the app embeds the exact published Rapier worker bytes. Pixel encoding defaults to effort 9 and quality 90; lossless: true selects quality 100. JPEG transcoding uses effort 9. WASM falls back to JavaScript; larger lossless images use available helper workers. Complete API.

Complete worker versus libjxl

Lossless RGBA8, including hidden RGB, through the complete published Rapier worker, compared with native libjxl 0.11.2. Effort numbers are each encoder's search budgets. Bpp means bits per pixel. Rapier ms is one call per configuration without warmup; libjxl ms is the median of three calls after one warmup.

| Input | Effort | Rapier bytes / bpp / ms (single) | libjxl bytes / bpp / ms (median) | | --- | ---: | ---: | ---: | | Light UI | 3 | 13,852 / 0.361 / 286.4 | 34,595 / 0.901 / 41.6 | | Light UI | 9 | 11,515 / 0.300 / 13937.6 | 12,687 / 0.330 / 406.9 | | Labelled drawing | 3 | 3,554 / 0.145 / 98.9 | 8,324 / 0.339 / 21.8 | | Labelled drawing | 9 | 1,644 / 0.067 / 7716.8 | 2,208 / 0.090 / 188.2 | | Painting | 3 | 150,434 / 6.121 / 135.4 | 140,851 / 5.731 / 44.1 | | Painting | 9 | 119,700 / 4.871 / 28956.9 | 121,901 / 4.960 / 1320.4 | | Photograph | 3 | 290,619 / 7.568 / 159.1 | 274,218 / 7.141 / 62.8 | | Photograph | 9 | 258,681 / 6.736 / 32734.2 | 254,579 / 6.630 / 2132.3 | | Terminal | 3 | 9,799 / 0.399 / 148.7 | 40,983 / 1.668 / 28.2 | | Terminal | 9 | 7,814 / 0.318 / 13108.0 | 11,729 / 0.477 / 246.3 |

Node 22.23.3 on Linux x64, AMD EPYC 9V74, CPU 0. One encoding thread per implementation. Rapier reports one call per configuration without warmup; libjxl reports the median of three calls after one warmup. Rapier uses automatic WASM; libjxl is native C++. The two implementations were measured separately on the same idle host. Timing includes each encode and output, excluding input transport/loading and decoding. Worker startup was 38.3 ms, measured separately. Every result preserves exact source RGBA; Rapier outputs also pass two independent decoders.

At effort 9, Rapier produces smaller files on these three document images and the painting; libjxl produces the smaller photograph. Native libjxl is faster in every measured row. Rapier's extra effort-9 search trades encoding time for smaller files and retains every earlier candidate. These desktop measurements do not predict browser or phone performance.

All four efforts, individual samples and reproduction.

Use the complete worker

Copy node_modules/rapier-jxl/dist/rapier-worker.js beside your page:

const worker = new Worker('./rapier-worker.js');
worker.onmessage = ({data}) => {
  if (data.ok) console.log(new Blob([data.bytes], {type: 'image/jxl'}));
  else console.error(data.error.message);
};
worker.postMessage({
  id: 1, operation: 'encode', width: 1, height: 1,
  data: new Uint8Array([255, 0, 0, 255]), options: {lossless: true}
});

For one offline HTML file, embed that complete worker as text and create it through a Blob URL. Copyable worker and module examples. Keep the MIT notice. No network download or decoder is needed for encoding.

The core and effort modules expose encode(rgba, width, height, options). Quality 100 preserves every sample, including RGB under transparent pixels; 1–99 is lossy. Alpha stays exact. Core/effort default to quality 100, and the separate effort entry defaults to effort 1. API and options.

Native inputs include 8/10/12/16-bit integers, binary16/32 floats, PQ/HLG and Rec. 2020. rapier-jxl/source reads supported PNG16/OpenEXR files. Displaying encoded output requires JPEG XL support.

Agent skills: Single-file apps · Photography.

API · Entry points and embedding · Agent reference · Comparisons · Browser example