Add support for newer chunks?

[svgeesus]

TweakPNG is a very handy tool, but it does not know about more recent chunks. It would be nice to add support for them:

• eXIf, registered in July 2017 and added to the core PNG spec in 2022
• acTL, fcTL and fdAT for Animated PNG
• cICP, added in 2022
• mDCv and cLLi, added in 2023

(Yes, the three APNG chunks indicate that they are private, but there is now a decade and a half worth of animated PNG images all over the web using those chunk names, so they can't be changed.)

See also the chunk ordering constraints.

[svgeesus]

Actually I see APNG is already supported and displays useful information, nice!

[jsummers]

Thanks for the suggestions. I hope to add basic support for cICP, mDCv, and cLLi. eXIf is a problem, though, and at this point I'm not planning anything more than the most minimal support for it.

[TPS]

@jsummers Any plans re: any of the other open issues? 🙇🏾‍♂️

[svgeesus]

Oh, EXIF in general is huge and sprawling, plus there are already tools like exiv2 which deal with it very comprehensively. So minimal support in tweakpng makes perfect sense!

For cICP there are certain combinations of values that are common - like 9 18 0 1 which means BT.2100 HLG, 9 16 0 1 which means BT.2100 PQ, 1 13 0 1 which means sRGB and 12 13 0 1 which means Display P3. My suggestion would be to check for that fairly small set and display more human-readable strings; and if it is some other combination, display the individual values.

[svgeesus]

Just a heads-up that an updated draft of PNG Third Edition was published today

[svgeesus]

Another heads up, PNG became a Candidate Standard 21 Sept 2023. Implementations of the new features are encouraged.