hdrfix - a tool for mapping HDR screenshots to SDR

This is a tool I wrote for my personal usage dealing with HDR (high dynamic range) screenshots of Microsoft Flight Simulator, as taken with Nvidia's GeForce Experience game overlay capture utility which saves a JPEG XR in 32-bit float precision scRGB, and an 8-bit-per-channel PNG with lower resolution information, but encoded with BT.2100 color space and transfer function.

Outputs files as regular SDR (standard dynamic range) PNGs in bog-standard sRGB colorspace. There are a few parameters for adjusting the conversion.

JPEG XR conversion is done with the jpegxr crate, which wraps Microsoft's BSD-licensed JPEG XR codec.

Also works with 16-bit float input as saved from the Windows Game Bar now and 10-bit RGB output from Xbox, however this is less tested.

Author, repo, etc

• Brooke Vibber <bvibber @ pobox.com>
• https://github.com/brion/hdrfix
• license: MIT (wrapper and conversion code), BSD (jpegxr library)

Dependencies

• clap for CLI setup
• time for speed checks in the CLI utility
• thiserror for error conglomeration
• rayon for multithreading
• glam for vector/matrix math
• png for reading input PNG
• mtpng for writing output PNG
• jpegxr for the JPEG XR C libray (and through it, bindgen and cc)
• oklab for perceptual color modifications
• mozjpeg for writing output JPEG
• half for reading 16-bit float input

Installation

From binary release download:

• download the latest release from https://github.com/brion/hdrfix/releases
• copy hdrfix.exe and (optionally) watch.bat into a desired directory
• for instance, C:\Users\<Yourname>\Videos\Microsoft Flight Simulator

From source checkout:

cargo install --path=.

From crates.io:

cargo install hdrfix

Usage

Basic conversion:

hdrfix screenshot.jxr output.jpg

Watching a folder, converting all newly-added *.jxr files to *-sdr.jpg:

hdrfix --watch=.

Note that an example Windows batch file watch.bat is included with settings for Flight Simulator screenshots, using this mode.

Interactive help!

hdrfix --help

Adjustable parmeters:

• --auto-exposure=N percentile of input signal to average to re-scale input to neutral mid-tone. Default is 0.5, which passes through input unchanged.
• --exposure=N adjusts the input signal by the desired number of f-stops up or down. The default is 0, passing through the original signal.
• --pre-levels-min sets the 0 point for input luminance, in either absolute units or as a percentile 0%..100%. Defaults to 0.
• --pre-levels-max sets 1.0 point for input luminance, in either absolute units or as a percentile 0%..100%. Brighter colors will be retained if using tone-mapping. Defaults to 1.
• --pre-gamma-N applies an exponential gamma curve to the input after scaling. The default is 1.0, passing through the original signal.
• --tone-map=A sets the HDR to SDR tone-mapping algorithm; choices are linear which will clip/correct anything brighter than 1.0, or one of hable, uncharted2 or aces filmic modes, or reinhard or reinhard-rgb which applies the Reinhard tone-mapping algorithm on either the luminance or separate RGB color channels. Luminance mode preserves colors better but can lead to out of gamut colors needing to be corrected; RGB mode will apply desaturation on brighter colors nicely but also can shift colors and alter luminance a bit. Default is hable, which is the same as uncharted2 but with different luma/desaturation treatment to match ffmpeg.
• --hdr-max=N sets the maximum luminance level for the Reinhard tone-mapping algorithm. Higher values will preserve more detail in very bright areas, at the cost of slightly poorer contrast in highlights. The default is 100% which checks for the brightest value from the image. A lower value will cause very bright details to blow out, but slightly lighten dark areas. Set as either a luminance in nits or a percentile of the input data.
• --saturation=N sets a coefficient for determining how fast desaturation occurs in Reinhard tone mapping. The default is 1 which does not desaturate.
• --post-gamma-N applies an exponential gamma curve to the output after tone mapping. The default is 1.0, passing through the original signal.
• --color-map=A sets the color-mapping algorithm for out of gamut colors after tone-mapping. Choices are clip which can alter color and brightness, darken which can cause major shifts in relative contrast but preserves color precisely, or desaturate which preserves luminance but desaturates color as necessary to fit in gamut. Default is clip.
• --post-levels-min sets the minimum output luminance level to retain, in either absolute 0..1 units or as a percentile 0%..100%. Darker colors will be flattened to black in output. Defaults to 0.
• --post-levels-max sets the maximum output luminance level to retain, in either absolute 0..1 units or as a percentile 0%..100%. Brighter colors will be flattened to white in output. Defaults to 1.
• --watch=P watches a folder path for new *.jxr files and converts them to SDR *-sdr.jpg files.

Recommended settings

I'm using the current default settings ("hable" tone mapping) for converting screenshots from Microsoft Flight Simulator, which look nice so far. Still tuning it up, so it may change.

Todo / roadmap

Definitely/short-term:

• add compression params for JPEG output

Maybe/later/no rush:

• see if can get a performance boost from Vec3A instead of Vec3 (so far it's been slightly slower when tested)
• a basic GUI with HDR and SDR side-by-side view
• GUI sliders for the adjustable parameters
• drag/drop and open/save dialog support
• extend to run a post-process script on --watch mode

Building

cargo build --release

Requires Rust and Cargo, and a C compiler. On Windows, install Visual Studio Community Edition with C++ development tools or else the command-line build tools. On Linux or Mac there may be some compilation problems at the moment as the jpegxr C library code is still being adapted.

You must install LLVM + Clang to complete a build due to the C code; on Windows you can get a release from https://github.com/llvm/llvm-project/releases/tag/llvmorg-12.0.0 or whatever the current release is. On Linux or Mac, use the system or user-preferred package manager.