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v1.0.0 — every option of the official image encoders, in one window

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@physics515 physics515 released this 01 Oct 20:09
v1.0.0
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Skidbladnir 1.0.0 is a free, open-source desktop app for Windows, Linux and macOS (experimental) that converts images to WebP, AVIF, JPEG XL and HEIC. It is the first Skidbladnir release that is not a prerelease. Copies installed from 0.8.0 onwards offer it as an update, each to its own edition.

Download

Your computer File
Windows 10 or 11, 64-bit Skidbladnir_1.0.0_x64-setup.exe
Mac with Apple silicon (experimental) Skidbladnir_1.0.0_aarch64.dmg
Mac with an Intel processor (experimental) Skidbladnir_1.0.0_x64.dmg
Ubuntu 22.04+, Debian 12+, Linux Mint 21+ Skidbladnir_1.0.0_amd64.deb
Any other 64-bit Linux with glibc 2.35+ Skidbladnir_1.0.0_amd64.AppImage

Not sure which edition? Take the files above, the standard edition. The files named Skidbladnir-GPL_… are the GPL edition: the same app, with x265 writing its HEIC (-L lossless, 4:4:4 and 4:2:2 chroma, 10-bit). Both are free; the licence matters only if you redistribute the app (Editions).

The other files are not installers. The .app.tar.gz files are for the in-app updater on a Mac. Skidbladnir-1.0.0-source.tar.gz is the complete source with every submodule, which GitHub's own "Source code" archives leave out. GitHub shows each file's SHA-256 beside it, for checking a download.

Opening it the first time

Nothing is code-signed yet, so Windows and macOS warn before they open it.

  • Windows: SmartScreen says Windows protected your PC. Click More info, then Run anyway. It installs for your account only, without administrator rights. With Smart App Control turned on, Windows blocks unsigned apps and offers no way past.
  • macOS (experimental): drag Skidbladnir to Applications and open it. When macOS says it cannot verify the app, close the message, open System Settings > Privacy & Security and click Open Anyway. If it says the app is damaged, run xattr -dr com.apple.quarantine /Applications/Skidbladnir.app in Terminal. CI builds the Mac app and launches it, but nobody has opened it on a real Mac yet, so Mac reports are very welcome.
  • Linux: sudo apt install ./Skidbladnir_1.0.0_amd64.deb, or chmod +x the AppImage and run it (it needs FUSE; otherwise run it with --appimage-extract-and-run).

What it is

Each of these formats has an official encoder, and each is a command-line tool with dozens of options. For a still image, every option of cwebp, avifenc (with libaom), cjxl and heif-enc (with Kvazaar) is a control in Skidbladnir, labelled with the flag it sets, and Skidbladnir writes the same bytes those tools write, built from the same library versions. CI checks that on every change: 3,387 conversions run through both the tools and Skidbladnir and must come out identical.

It reads PNG, JPEG (including Photoshop's CMYK), TIFF, WebP, GIF, AVIF, JPEG XL, HEIC, PNM/PAM and PFM; converts animated GIF and WebP to animated WebP; keeps colour profiles, Exif and XMP the way each tool keeps them; and shows the result beside the original before anything is written. Conversion happens on your computer: the app's one network request is the update check at startup.

Where the claim stops

The README lists the limits under What "every option" means. In short:

  • Still images, plus animated WebP as img2webp and gif2webp write it. Their -mixed, -min_size, -kmin/-kmax, -loop and per-frame options are not offered yet, and neither are animated AVIF, JPEG XL or HEIC, or files built from several images.
  • The same encoders, built the same way: libwebp 1.6.0, libavif 1.4.2 with libaom 3.15.1, libjxl 0.12.0, libheif 1.23.5 with Kvazaar 2.3.2. A packaged avifenc usually links libyuv and writes other bytes.
  • Bytes are compared on Linux x86-64. The Windows and macOS builds link the same sources.
  • Two TIFF-alpha cases differ: a TIFF with straight alpha keeps its true colours where cwebp darkens it (on purpose), and a TIFF with premultiplied alpha written to HEIC keeps its true colours where heif-enc darkens it (not decided yet).
  • The GPL edition's HEIC is checked by decoding it, not byte for byte.
  • Y4M, PGX, EXR and raw-pixel input are not read yet.

New since 0.15.0

  • Linux: the installers are now built on Ubuntu 22.04, so they run on Ubuntu 22.04, Debian 12, Linux Mint 21 and newer. 0.14.0 and 0.15.0 needed glibc 2.39 and did not start there. Every release run now checks the floor, and installs the .deb on Ubuntu 22.04 and Debian 12.
  • macOS: the app is now signed ad hoc, so macOS offers Open Anyway instead of calling it damaged. Every release run checks the signature, launches the app on macOS (the Intel build under Rosetta) and checks that it keeps running.
  • Releases are stable from this one, so the latest release link always works. The release page now carries only the installers and the source.
  • The README now opens with what Skidbladnir is, which file to download, and how to open it the first time on each system.
  • A security policy with private reporting, and issue forms for bug reports and for output that differs from a reference tool's.

0.15.0's fixes are included: a premultiplied-alpha TIFF to WebP, a lossy WebP or a HEIC to HEIC, and a still GIF to JPEG XL now match their tool byte for byte. 0.14.0 had claimed them early.

Known gaps

  • Not code-signed on any platform.
  • macOS is experimental until a person has run it on a real Mac.
  • An AVIF, JPEG XL or HEIC encode cannot be cancelled mid-file.
  • No builds for 32-bit systems, Linux on ARM or Windows on ARM.
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