pXL Compare Support

How do I install pXL Compare?

Download the ZIP file, open it to unzip, and drag pXL Compare into your Applications folder. The app is signed and notarized by Apple, so it opens like any other Mac app.

The first time it opens, the Required Tools window shows which encoders are installed. You can close it and come back to it any time from the Help menu.

What do I need to run pXL Compare?

A Mac running macOS Tahoe 26.4 or later. JPEG (System) and HEIF (System) work right away. The other eight encoders need free command-line tools, which you install once.

How do I install the encoders?

Install Homebrew from brew.sh if you don’t have it, then run this in Terminal:

brew install jpeg-xl libavif webp libheif jpeg-turbo exiftool

JPEGli isn’t available from Homebrew. To use it, build it from Google’s source code:

brew install git cmake ninja pkg-config clang-format googletest doxygen graphviz
git clone https://github.com/google/jpegli.git
cd jpegli
./deps.sh
SKIP_TEST=1 ./ci.sh release
mkdir -p ~/bin
cp build/tools/cjpegli build/tools/djpegli ~/bin/

A panel says a tool is missing. What do I do?

Open Required Tools (⌥⌘R, or from the toolbar or Help menu). It lists every encoder, shows whether it’s installed, and gives you a command you can copy. After installing, click Re-check. You don’t need to restart the app.

My tools are installed somewhere unusual. Can pXL Compare find them?

Yes. pXL Compare looks in ~/bin, /opt/homebrew/bin, /usr/local/bin and the standard system folders. To add another folder, such as a jpegli build folder or /opt/local/bin, open Settings and add it under Custom Tool Directories. Those folders are searched first.

Why are the System encoders so much faster?

JPEG (System) and HEIF (System) run inside the app. The other encoders start a separate program and read and write files for every run, and that overhead is included in their speed. Compare speeds within each group, especially on small images.

Why does libjpeg-turbo score lower on some images?

libjpeg-turbo only accepts 8-bit sRGB, so wide-color images are converted to sRGB before encoding. Its SSIMULACRA2 score can come out lower than codecs that receive the full 16-bit source.

Does pXL Compare upload my images?

No. Everything runs on your Mac. Working files go in /tmp/CompressionComparison and are deleted automatically: as soon as they’re replaced, when you quit, or after 24 hours at the latest.

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