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PNG has been updated for the first time in 22 years — new spec supports HDR and animation
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this post was submitted on 03 Jul 2025
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But is it backwards compatible with an old version that can't be updated?
Yeah, this was my first thought. How many slightly older, no-longer-being-updated pieces of software will fail to open the new version? Hopefully it’s built in a way that it just falls back to legacy and ignores the extra information so you can at least load the file.
This is all the article mentions. I hope you’re right about the backwards compatibility.
I remember the Wild West Web days when it was a toss up seeing if animated Gifs, transparencies in images, or the specific hexadecimal for your personal shade of purple you created would render properly between browsers.
Lies! That gif is sped up 2000%!
LOL, I heard that gif. Timed it in my mind, on the money OP.
Ooh, that was the coaster company, I remember them.
I mean, that's already how animated .gifs work. If somehow you manage to load one into a viewer that doesn't support the animation functionality it will at least dutifully display the first frame.
How the hell you would manage to do that in this day and age escapes me, but there were a fair few years in the early '90s where you might run into that sort of thing.
Probably most notably the iOS photos app until like 2014.
Edit: just checked. iOS 11 in 2017 added gif support to photos
I’ll also add, safari supported animated gifs for a long time before that and you could still save them in safari like any other image. But photos would only show the first frame like you said. When 11 came out they played like normal.
One example is piefed unfortunately. Animated gifs as avatar or banner don't animate currently as far as I can tell.
Those are displayed in browser, right? The only reason that would be happening is if Piefeed is recompressing images and their code is not smart enough to identify an animated .gif and act accordingly.
Yeah in browser. I should probably open an issue ticket if nobody else noticed yet.
Relevant issue: https://codeberg.org/rimu/pyfedi/issues/665
tl;dr - it's an issue with the pillow image library in python. It's on our radar though. I got posts working, but you have to click through, the thumbnail still isn't animated.
Oh good looks like you're on it already nice! The only other thing I noticed missing moving from Lemmy was sorting Top by "x" amount of time, but I see there's an open issue for that as well already. Nothing for me to do lol.
Still lots of things to do :)
Lemmy has been at it for years at this point while piefed only started up a bit over a year ago I think? In any case, I have only been a contributor for maybe a couple weeks, so lots of catching up to do!
I'll bet you a shiny penny that's what it is. The backend recompresses things to some other format, probably a low bitrate JPEG, in order to save space and/or in case some joker uploads a 90 megabyte uncompressed TIFF image to use as a profile pic, or something.
Speaking for animation, your browser probably already supports APNG. APNG is 21 years old and has decent adoption. But it’s officially part of the club.
That said, APNGs are fat as fuck and they’re a pretty old solution to animated graphics with an alpha channel. Don’t expect to see everyone making APNGs all of the sudden. There is a reason why people have kept it at a distance.
Some of this is paving the cowpath - the animated PNG stuff is 20 years old and e.g. Firefox has had support since March 2007.
The PNG format is made of chunks that have determined roles, and provides provisions for newer "standardized" chunks alongside the custom chunks it had supported until now. It is likely that PNG made with newer software that does not use new features, or uses only additional features, will remain readable by older software to some extent.
Probably means there will be new PNGs that old software won't be able to open.
It makes sense, right? Is there a way around that when adding new features to a file format?
The alternative is to make another file format for clarity, but it's not really what you want to do.
That depends. Something like HDR should be able to fall back to non-HDR since it largely just adds data, so if the format specifies that extra information is ignored, there's a chance it works fine.
I'm not sure you can turn an hdr image into a regular one just by snipping it down to 8 bits per channel and discarding the rest.
I mean it would work but I'm not certain you'll get the best results.
And that's probably enough. I don't know enough about HDR to know if it would look anything like the artist imagined, but as long as it's close enough, it's fine if it's not optimal. Having things completely break is far less than ideal.
You'd probably get some colours that end up being quite off target. But you'll get an image to display. So in the end it depends on how much "not optimal" you're ready to accept.
Right, and it depends on what "quite off target" means. Are we talking about greens becoming purples? Or dark greens becoming bright greens? If the image is still mostly recognizable, just with poor saturation or contrast or whatever, I think it's acceptable for older software.
So it depends on the specific HDR encoding used, Rec2020 is the most common ones you'll see (It's meant for "pure" setups, i.e. where the source and output are tightly linked, e.g. gaming consoles or blu-ray, or so) and the raw data won't look great. While something like HLG (Hybrid-Log Gamma) is designed for better fallback (As it's meant for TV broadcast, where the output device is "whatever TV the user has"), so should just look dimmer.
This is a HDR screenshot I took of Destiny 2, which uses Rec2020, tone mapped to SDR
And here's the raw screenshot data from before tonemapping.
If the second image had all the right HDR metadata, and the viewer supported it properly, then both images would match.
I see, but the animation feature cant be compatiable no?
Likely, you'll see the first frame only on older software. Encoding animation in a dedicated animation chunk and using the base spec for the first keyframe sounds like the sane thing to do, so they likely did that.
I'm not going to look into it now, because I would then have to implement it. :D
Haha dont worry, just curious. Your answer is good!
I'll tell you if I can find some new files for testing.
Even JPEG isn't always back compatible either. I loaded an image into my software which uses some ancient library internally, and it swapped the blue and red channels.
Yes that's why its so great
I'm probably gonna be massively downvoted for saying the forbidden word but I asked AI to do a summary with references of the forward and backward compatibility of PNG's new version:
Based on recent search results, the new PNG specification (Third Edition) and its reference library (libpng) maintain strong backward compatibility while introducing modern features. Here's a detailed compatibility analysis:
🔄 1. Backward Compatibility (Viewing Old PNGs with New Lib)
png_struct/png_infointernals since 1.5.0) ensures older apps usingpng_get_*/png_set_*functions remain compatible. Direct struct access, deprecated since 1.4.x, may break in libpng 2.0.x (C99-only) .png_image_free()) were patched in libpng 1.6.37+, making the new lib safer for decoding old files .⚠️ 2. Forward Compatibility (Viewing New PNGs with Old Lib)
IHDRorIDATremain unchanged .mDCvchunk. Older libs ignore HDR data, falling back to SDR, which may cause color inaccuracies .eXIfchunks are ignored by legacy decoders, losing metadata like GPS or copyright info .📊 Compatibility Summary
🔧 3. Implementation and Industry Adoption
💎 Conclusion
For developers: Use
png_get_valid(png_ptr, info_ptr, PNG_INFO_mDCv)to check HDR support and provide fallbacks .!<
downvoters: is it wrong?
I don't know. If the poster couldn't be bothered to fact-check, why would I? It is just safer to assume that it can be misinformation.
If you prefer to know nothing about PNG compatibility rather than something that might be true about PNG. That's fine but definitely not my approach.
Also, as I said to another commenter. Critical thinking is not some tool you decide to use on some comments and not others. An AI answer on some topics is actually more likely to be correct than an answer by a human being. And it's not some stuff I was told by an AI guru it's what researchers are evaluating in many universities. Ask an human to complete various tasks and then ask the AI model and compare scientifically the data. And it turns out there is task where the AI outperforms the human pretty much all the time.
YET on this particular task the assumption is that it's bullshit and it's just downvoted. Now I would have posted the same data myself and for some reason I would not see a single downvote. The same data represented differently completely change the likelihood of it being accurate. Even though at the end of the day you shouldn't trust blindly neither a comment from an human or an AI output.
Honestly, I'm saddened to see people already rejecting completely the technology instead of trying to understand what it's good at and what it's bad at and most importantly experiencing it themselves.
I wanted to know what was generative AI worth so I read about it and tried it locally with open source software. Now I know how to spot images that are AI generated, I know what's difficult for this tech and what is not. I think that's a much healthier attitude than blindly rejecting any and all AI outputs.
You put way too much trust in AI. AI is seldom right. It is however very good at sounding like it knows what it's talking about. It's like a conservative podcaster.
Considering it named CVE-2019-7317, which was fixed in April 2019, it's already hallucinating and not worth reading further into it.
As you can see it's irrelevant apparently. If it's AI generated it will be downvoted.
It's not irrelevant, it's that you don't actually know if it's true or not, so it's not a valuable contribution.
If you started your comment by saying "This is something I completely made up and may or may not be correct" and then posted the same thing, you should expect the same result.
I did check some of the references.
What I dont understand is why you would perceive this content as more trustworthy if I didn't say it's AI.
Nobody should trust blindly some anonymous comment on a forum. I have to check what the AI blurbs out but you can just gobble the comment of some stranger without exercising yourself some critical thinking?
As long as I'm transparent on the source and especially since I did check some of it to be sure it's not some kind of hallucination...
There shouldn't be any difference of trust between some random comment on a social network and what some AI model thinks on a subject.
Also it's not like this is some important topic with societal implications. It's just a technical question that I had (and still doesn't) that doesn't mandate researching. None of my work depends on that lib. So before my comment there was no information on compatibility. Now there is but you have to look at it critically and decide if you want to verify or trust it.
That's why I regret this kind of stubborn downvoting where people just assume the worse instead of checking the actual data.
Sometime I really wonder if I'm the only one supposed to check my data? Aren't everybody here capable of verifying the AI output if they think it's worth the time and effort?
Basically, downvoting here is choosing "no information" rather than "information I have to verify because it's AI generated".
Edit: Also I could have just summarized the AI output myself and not mention AI. What then? Would you have checked the accuracy of that data? Critical thinking is not something you use "sometimes" or just "on some comments".
So why "research" it with AI in the first place, if you don't care about the results and don't even think it's worth researching? This is legitimately absurd to read.
You realize that if we wanted to see an ~~AI~~ LLM response, we'd ask an ~~AI~~ LLM ourselves. What you're doing is akin to :
I understand that. It's the downvoting of the clearly marked as AI LLM response. Is it detrimental to the conversation here to have that? Is it better to share nothing rather than this LLM output?
Was this thread better without it?
Is complete ignorance of the PNG compatibility preferable to reading this AI output and pondering how true is it?
Now I think this conversation is getting just rude for no reason. I think the AI output was definitely not the "I'm lucky" result of a Google search and the fact that you choose that metaphor is in bad faith.
I'll spell out for you why I feel these two things are the same. You're welcome to disagree, but maybe it will give you some pointers as to why a lot of people are annoyed by these LLM copy-pasta.
First, a note for your ego : Remember, we don't know you! You might have read through the whole thing that the LLM generated, and then cross-referenced the sources it gave you and then found some more, and you established the veracity of what it told you. OR you might have not bothered and just copy-pasted it for the clout, I guess, which is what the majority of LLM users do when publishing these answers. Ask for some explanations on how to solve a problem to a student who let a LLM give them the answer to an assignment instead of doing the work, if you need proof. 9/10 won't be able to, because they didn't bother to understand it - and I'm being generous in my statistics, in my experience.
There's also a lot of research that hints that the long term effect of using this tool in that way are deleterious to your critical thinking skills.
We don't know you, so, chances are you're in the lot of the majority, as far as we're concerned.
Then, given that you probably didn't put much effort into this text (as far as we can tell), there is an imbalance of effort required for us to look through it critically. Why the fuck would we put in the effort, if you most likely were not keen in putting so much in yourself? That's kinda disrespectful, and egotistical. And also why I feel I am justified to assume that ctrl+c/ctrl+v an LLM output directly is tantamount to copy pasting a list of link from google. If you went through the trouble of validating the LLM output, how about just writing with your own word what you just realized / learned / validated? You can even dictate with tons of FOSS software nowadays if you're unable to type!
So that's what I have for now, food for your thoughts I hope. I'm sure I could find more reasons, but I'm going to go do something fun instead.
Yes.
I, and I assume most people, go into the comments on Lemmy to interact with other people. If I wanted to fucking chit-chat with an LLM (why you'd want to do that, I can't fathom), I'd go do that. We all have access to LLMs if we wish to have bullshit with a veneer of eloquency spouted at us.
Are you really asking why advertising that "the following comment may be hallucinated" nets you more downvotes than just omitting that fact?
You're literally telling people "hey, this is a low effort comment" and acting flabbergasted that it gets you downvotes.