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PNG to JXL Converter: Lossless, Smaller, Private

Convert PNG to JXL (JPEG XL) in your browser. Lossless mode keeps every pixel and the alpha channel while cutting size below PNG. No uploads, fully client-side.

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How It Works

JPEG XL's lossless mode is the reason this conversion exists. PNG already stores every pixel exactly, so the only thing worth changing is the container, and JXL's modular (lossless) coder packs the same pixels into fewer bytes than PNG's DEFLATE. Re-encode a PNG to JXL at distance 0 and you get back an identical image at a smaller size, which is why people sitting on icon sets, screenshots, flat UI art, and large PNG archives reach for it. This tool decodes your PNG with the browser's native decoder, draws it to a canvas, and pulls the raw RGBA pixels. Those pixels go straight to the @jsquash/jxl encoder compiled to WebAssembly, run at distance 0 (mathematically lossless) with progressive encoding. The decoded pixels and the alpha channel are reproduced exactly; only the byte layout changes. There is no lossy setting here and no quality slider to misconfigure, so the output is always a faithful copy of the input. The whole pipeline stays in the page. Your PNG is read into memory, encoded, and handed back as a .jxl download. Nothing is uploaded, so the conversion keeps working if you pull the network cable after the page loads, and the file never touches a server.

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Convert toJXL

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Key Features

  • No file uploads required - works offline
  • 100% privacy focused - client-side processing
  • Browser powered - no software installation
  • Fast processing - WebAssembly technology
  • Free forever - no premium accounts

Supported File Formats

.png

Output Format: JXL

Technical Specifications

input Format PNG (Portable Network Graphics), with alpha channel
output Format JXL (JPEG XL, ISO/IEC 18181)
compression Type JXL modular coder, lossless (encoder fixed at distance 0)
quality Retention Pixel-for-pixel identical; alpha channel preserved
color Space Support Decoded to 8-bit RGBA via canvas; sRGB pixel values preserved
max Resolution Limited only by your device's memory (100 MB upload cap)
processing Time Instant, runs in your browser

Key Benefits

  • Lossless by design: every PNG pixel and the alpha channel come back exactly
  • Typically smaller than the source PNG, with the largest gains on photos and gradients
  • Runs fully client-side, so the PNG never leaves your device
  • Keeps working offline once the page has loaded
  • No quality slider to get wrong, the output is always a faithful copy
  • Transparency carries over intact for logos, icons, and overlays

Common Use Cases

  • Shrinking large PNG asset libraries for archival without altering a pixel
  • Storing UI icons, screenshots, and flat illustrations more compactly than PNG
  • Preparing exact-copy images for Apple platforms that decode JXL natively
  • Keeping a master lossless copy that is smaller on disk than the original PNG
  • Cutting storage and backup size for design and screenshot collections
  • Re-encoding photographic PNGs that compress poorly as PNG

Pro Tips

  • Run already-optimized PNGs through it too; JXL often still finds extra savings DEFLATE missed
  • Keep the original PNG as a fallback until your delivery targets decode JXL reliably
  • For web delivery, serve WebP or AVIF and reserve JXL for storage or Apple platforms
  • Convert very large canvases on a machine with ample RAM, since the whole image loads into memory
  • Expect bigger savings on photos and gradients than on small, flat icons

Frequently Asked Questions

Always. The encoder is fixed at distance 0, JXL's mathematically lossless setting. Because PNG is lossless to begin with, the decoded pixels and the alpha channel come out bit-for-bit identical. The image is unchanged; only how the pixels are stored differs, which is what makes the JXL smaller.
Usually, yes. JXL's lossless modular coder generally beats PNG's DEFLATE, with the biggest wins on photographic content, gradients, and large flat areas. A tiny PNG or one already crushed by oxipng or pngquant may shrink only a little. The savings come purely from better compression, not from discarding anything.
Yes. The alpha channel is read out of the PNG and encoded into the JXL, so semi-transparent edges, drop shadows, and fully transparent backgrounds all survive. That makes it safe for logos, UI assets, and overlays where the transparency is the point.
Support is uneven, so plan for it. Safari on macOS Sonoma and iOS 17 or later opens JXL; Chrome and Firefox do not decode it natively. For viewing and editing, GIMP, ImageMagick, XnView, and macOS Preview handle JXL. Treat JXL as a storage and Apple-platform format and keep a PNG, WebP, or AVIF copy for the open web.
No. The PNG is decoded and re-encoded entirely in your browser through WebAssembly. There is no upload, no server step, and nothing kept afterward. Disconnect from the network after the page has loaded and the conversion still runs, which is the simplest way to confirm it.
For lossless work JXL usually compresses tighter than lossless WebP and is competitive with lossless AVIF, so it wins when you want the smallest exact copy or a long-term archive. If the file has to render in any browser today, lossless WebP or AVIF is the safer choice because of decoder support.
The tool caps uploads at 100 MB and otherwise has no fixed pixel limit. The real ceiling is your device's memory, since the full image is decoded into RAM and re-encoded there. Ordinary large PNGs convert fine on a normal laptop; an enormous canvas may need a machine with more memory.
It runs one file per pass to keep memory predictable. Encoding is quick, so converting a folder of icons or screenshots back to back is fast in practice even without a batch queue.