FluffyBench

Can JPEG XL keep a JPEG unchanged?

Yes. JPEG XL can tuck a JPEG inside itself and give you the exact same file back later. A fresh conversion in FluffyBench can look the same and still take more space.

FluffyBench · 6 min read · Reviewed

Can JPEG XL preserve the original JPEG file?

Yes, through a feature called reversible JPEG transcoding. JPEG XL is a picture format with the extension .jxl, and it can carry a JPEG's compressed data so compatible software can rebuild the original JPEG file. Think of putting a sealed letter inside another envelope: unwrap it and you've still got the same letter.

FluffyBench's JPEG XL converter takes a different route: it opens the JPG as picture pixels and encodes a new JXL. Even if every pixel matches, the original JPEG file isn't inside it.

Reversible JPEG transcoding preserves compressed JPEG data; FluffyBench makes a fresh JXL from decoded pixels.
Recovering the same file and keeping the same picture pixels are different jobs. How we reviewed

What happens when FluffyBench converts a real JPG?

A fresh encode starts from the expanded picture, so it doesn't inherit the JPG's compact storage. We took a National Park Service bison photo that was already a JPG and made two new JXL files from it.

Both new files were larger than the JPG. The Quality 100 JXL was about 5.4 times its size, so neither conversion saved storage for this photo.

One bison photo: JPG and fresh JXL file sizes

Scale maximum: 6.1 MB

Original JPG
1.1 MB
Quality 92 JXL
1.2 MB
Quality 100 JXL
6.1 MB
One bison JPG, two new JXL files, measured on 2026-10-15 with the earlier encoder. Sizes are for whole files.

What happened to the picture? Start with the pale rim of the bison's horn, marked here.

Whole bison display photo with a red locator on the horn's pale rim, identifying the enlarged detail below.
The marked horn detail is enlarged below. · Photo: NPS / Neal Herbert, Public domain: Full Granting Rights, via National Park Service NPGallery.

At Quality 92, some pixel values changed. At Quality 100, every decoded pixel matched the JPG's decoded picture, yet the much larger JXL still wasn't the original JPEG file.

Original JPG

Original horn detail: gray horn, pale rim and soft tan coat.

Look at the pale horn edge against the soft coat.

60 × 45 px; 8× magnification.

Picture decoded from the original JPG.

1.1 MB

Quality 92 JXL

Same horn detail after Quality 92 JPEG XL encoding.

The same patch, enlarged by the same amount.

60 × 45 px; 8× magnification.

Changed pixel values in the decoded picture.

1.2 MB

Quality 100 JXL

Quality 100 matched the source horn detail at every pixel.

60 × 45 px; 8× magnification.

Every decoded pixel matched the JPG's decoded picture.

6.1 MB

Where Quality 92 changed pixels

Red marks changed color values; dark marks matching positions.

60 × 45 px; 8× magnification.

Red marks changed color values; dark marks matching positions.

A close look checks appearance; a decoded-pixel comparison establishes exact equality. Sizes are for the whole files. · Photo: NPS / Neal Herbert, Public domain: Full Granting Rights, via National Park Service NPGallery.

Should you convert your JPG to JPEG XL?

Convert when you need a JXL, or when the new file is smaller and looks right. For a recoverable original JPEG, you need software with reversible JPEG transcoding.

Recover the JPEG: use reversible JPEG transcoding. Make a new JXL: use FluffyBench's JPEG XL converter. Share an image: choose a format the recipient can open.
An app that opens JXL doesn't necessarily recover an original JPEG from it.

For sharing, the deciding check is the recipient's actual app. If you don't know what it can open, JPG is another option. Our browser and app image-format guide helps you check compatibility without assuming every app handles JXL alike.

If you need information stored alongside the picture, such as camera tags, FluffyBench's fresh JXL doesn't carry over the source container's metadata. See what happens to image metadata during conversion before choosing a new file as your archive copy.

Doing it in FluffyBench

FluffyBench's JPEG XL converter makes a new JXL from your JPG. This walkthrough uses a different photo from the bison JPG above: its JXL comes out smaller, so judge storage savings from your own result's size readout.

  1. JPEG XL workspace with Choose images, To JPEG XL and the Settings button.
    JPEG XL workspace with Choose images, To JPEG XL and the Settings button.
    Step 1. Choose a JPG. On FluffyBench's JPEG XL converter, To is already set to JPEG XL. Keep your original JPG.
    1. Choose images opens your device’s file picker.
    2. To is set to JPEG XL.
    3. The gear button (JPEG XL · 92%) opens Settings.
  2. Quality slider showing 92 in JPEG XL Settings.
    Quality slider showing 92 in JPEG XL Settings.
    Step 2. Quality changes how much picture detail the JXL keeps. It starts at 92; leave it there for this job.
    1. Leave Quality at 92.
  3. Toolbar button used to close JPEG XL Settings.
    Toolbar button used to close JPEG XL Settings.
    Step 3. Tap Settings again to close the output controls.
    1. Settings closes the panel you’ve just used.
  4. Convert button ready for the selected JPG.
    Convert button ready for the selected JPG.
    Step 4. Press Convert to make a new JXL.
    1. Convert creates the new JXL.
  5. Completed JXL result, output size and Download.
    Completed JXL result, output size and Download.
    Step 5. Compare the original and JXL sizes before saving. Download saves the new JXL to your device.
    1. Compare with the original; use the JXL for storage savings if it's smaller.
    2. Download saves your JXL.

FluffyBench Image Viewer lets you inspect a JXL without re-encoding it. To send an existing JXL to an app that needs PNG, use FluffyBench's PNG converter.

FluffyBench JPEG XL converter: make a new JXLFluffyBench PNG converter: save JXL as PNG

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