pngcheck 4.0.1 is out to check your PNG files

[ctruta]

Hello, everyone,

Wanna know what's new with the good old pngcheck?

https://github.com/pnggroup/pngcheck
https://github.com/pnggroup/pngcheck/releases/tag/v4.0.1

The last official release announcement was for version 3.0.3 back in April 2021. We went through a Git history reconstruction and a "missed announcement opportunity" for version 4.0.0, and that's alright, given how the publication of PNG Third Edition was soooo much more interesting.

Any guess: what makes pngcheck version 4.0.1 soooo much more interesting?...

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PNG Third Edition brought us HDR support via three new chunks: cICP (Coding Independent Code Points), mDCV (Mastering Display Color Volume), and cLLI (Content Light Level Information). It also finally standardized APNG — yes, the animated PNG format that Firefox shipped in 2008 and everyone else adopted over the years is now officially part of the spec. And then, PNG Fourth Edition (still in draft) brings caBX for content credentials, a.k.a. the "is this AI-generated?" metadata that the C2PA folks are working on.

The new pngcheck understands all of these. It will tell you if your HDR PNG is using BT.2100 PQ or P3D65, it will validate your APNG frame control chunks, and it will flag that shiny new caBX chunk when it spots one.

Oh, and it also knows about iDOT, Apple's parallel-decoding chunk — created by Apple in 2011, used by them consistently with Xcode, and only just now registered in the PNG Extensions document. Better late than never!

The maintainership torch has been passed as well. Greg Roelofs, who shepherded pngcheck from version 1.6 through 3.0.3, handed the reins to Chris Lilley. I'm helping out as co-maintainer, which mostly means I get to write build files and pester Chris about edge cases.

Speaking of which: pngcheck now builds with CMake as the primary build system. zlib is a proper required dependency now (no more USE_ZLIB ifdef soup). We have CI workflows on GitHub Actions for Linux, macOS, and Windows. The Windows builds auto-expand wildcards like civilized platforms do. I kid you not: this project, as old as PNG itself, is just as modern as a modern project can be!

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Sincerely,
Cosmin

[ace-dent]

Nice! Historically Greg provided binaries... will these be added to the GitHub release(s)?
I wonder if homebrew needs a nudge to point to the new repo?
🙏

[ctruta]

Compiled binaries:
In principle, yes. In practice, I didn't get to it. We have a Release action at
https://github.com/pnggroup/pngcheck/blob/bd33ad6490/.github/workflows/release.yml
We got this working after the v4.0.1 tag, mind you, but we can still manually create and upload binaries to the v4.0.1 release.

Homebrew:
Yes, they need a nudge. They're still at v3.0.3, pointing to the old libpng.org URL.

Windows (MSYS2):
I was convinced they had pngcheck, but after a cursory look at
https://packages.msys2.org/packages/
I realized they don't. If you're interested in contributing, a nudge there would be worthwhile, too.

[svgeesus]

Now to get Linux distros to ship this version by default.

[ctruta]

Given that we did send an announcement this time around, we should expect a better uptake.

[Checking...]

Fedora Rawhide 👍 https://packages.fedoraproject.org/pkgs/pngcheck/pngcheck/index.html

Still waiting for the others. December could be a "slow month" for all I know, but we'll give it another look in January, and we'll start sending them friendly pokes and nudges if necessary.

[ctruta]

Hello, Happy New Year! 🥳

I confirm that the uptake in the Linux world is as good as it gets. And it's not only Fedora and Debian/Ubuntu, but also SUSE which jumped from 3.0.3 straight to 4.0.1. This time it's really all the usual suspects from the conservative Debian all the way to the bleeding-edge Arch Linux who picked up either 4.0.0 or 4.0.1.

If the release of 4.0.0 eluded a bunch of distros earlier in 2025, it very likely happened due to the lack of an announcement.

Lesson learned ✌️🤓