jxr2uhdr

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Convert JPEG XR (.jxr) HDR images to Ultra HDR JPEG files.

🌐 Try it online: https://tfx2001.github.io/jxr2uhdr/ — Browser-based converter powered by WebAssembly, no installation required.

Ultra HDR is a backward-compatible JPEG format developed by Google that embeds an HDR gain map alongside a standard SDR base image. The resulting file can be displayed as normal SDR on legacy devices, while HDR-capable displays render the full high dynamic range.

Use Case

NVIDIA's in-game screenshot capture tool saves HDR frames as JPEG XR (128bpp RGBA float). This tool converts those captures directly to Ultra HDR JPEG, which is natively supported on Android 14+ and modern displays.

Current conversion pipeline:

flowchart LR
    input["input.jxr<br/>JPEG XR HDR<br/>128bpp RGBA f32 or 64bpp RGBA f16"]
    decode["Decode JPEG XR<br/>jpegxr::ImageDecode"]
    image["Linear RGBA image buffer"]
    sdr["SDR base branch"]
    tonemap["Hable filmic tonemapping<br/>linear RGB to sRGB RGBA8888"]
    sdr_raw["SDR RawImage<br/>BT.709 / sRGB / full range"]
    hdr["HDR intent branch"]
    scale["Scale scRGB 80-nit reference white<br/>to Ultra HDR 203-nit linear white"]
    hdr_raw["HDR RawImage<br/>RGBA f16 / linear / full range"]
    peak["Estimate target display peak brightness<br/>from HDR RGB peak percentile"]
    encoder["libultrahdr Encoder"]
    output["output.jpg<br/>Ultra HDR JPEG<br/>SDR base + HDR gain map"]

    input --> decode --> image
    image --> sdr --> tonemap --> sdr_raw --> encoder
    image --> hdr --> scale --> hdr_raw --> encoder
    image --> peak --> encoder
    encoder --> output

Loading

Installation

cargo install --path jxr2uhdr-cli

Or build without installing:

cargo build --release -p jxr2uhdr
# Binary: target/release/jxr2uhdr

Usage

jxr2uhdr --input <INPUT> --output <OUTPUT> [--quality <QUALITY>]

Options:
  -i, --input <INPUT>      Input JXR file path
  -o, --output <OUTPUT>    Output Ultra HDR JPG file path
  -q, --quality <QUALITY>  Quality of the output base JPEG (0-100) [default: 90]
  -h, --help               Print help
  -V, --version            Print version

Example:

jxr2uhdr -i screenshot.jxr -o output.jpg
jxr2uhdr -i screenshot.jxr -o output.jpg --quality 95

Log verbosity can be controlled via the RUST_LOG environment variable:

RUST_LOG=debug jxr2uhdr -i screenshot.jxr -o output.jpg

Build

# Debug build
cargo build -p jxr2uhdr

# Release build (recommended for production use)
cargo build --release -p jxr2uhdr

Test

cargo test --workspace

License

MIT