[lxgr]

As in, a clear way to detect whether a given file is lossy or lossless?

I was thinking that too, but on the other hand, even a lossless file can't guarantee that its contents aren't the result of going through a lossy intermediate format, such as a screenshot created from a JPEG.

[snvzz]

I meant like a filename convention, and tags in the file itself.

[149765]

There is some sort of tag, jxlinfo can tell you if a file is "lossy" or "(possibly) lossless".

[stavros]

Presumably you can look at the file and tell which mode is used, though why would you care to know from the filename?

[crazygringo]

I find it incredibly helpful to know that .jpg is lossy and .png is lossless.

There are so many reasons why it's almost hard to know where to begin. But it's basically the same reason why it's helpful for some documents to end in .docx and others to end in .xlsx. It tells you what kind of data is inside.

And at least for me, for standard 24-bit RGB images, the distinction between lossy and lossless is much more important than between TIFF and PNG, or between JPG and HEIC. Knowing whether an image is degraded or not is the #1 important fact about an image for me, before anything else. It says so much about what the file is for and not for -- how I should or shouldn't edit it, what kind of format and compression level is suitable for saving after editing, etc.

After that comes whether it's animated or not, which is why .apng is so helpful to distinguish it from .png.

There's a good reason Microsoft Office documents aren't all just something like .msox, with an internal tag indicating whether they're a text document or a spreadsheet or a presentation. File extensions carry semantic meaning around the type of data they contain, and it's good practice to choose extensions that communicate the most important conceptual distinctions.

[lxgr]

> Knowing whether an image is degraded or not is the #1 important fact about an image for me

But how can you know that from the fact that it's currently losslessly encoded? People take screenshots of JPEGs all the time.

> After that comes whether it's animated or not, which is why .apng is so helpful to distinguish it from .png.

That is a useful distinction in my view, and there's some precedent for solutions, such as how Office files containing macros having an "m" added to their file extension.

[crazygringo]

Obviously nothing prevents people from taking PNG screenshots of JPEGs. You can make a PNG out of an out-of-focus camera image too. But at least I know the format itself isn't adding any additional degradation over whatever the source was.

And in my case I'm usually dealing with a known workflow. I know where the files originally come from, whether .raw or .ai or whatever. It's very useful to know that every .jpg file is meant for final distribution, whereas every .png file is part of an intermediate workflow where I know quality won't be lost. When they all have the same extension, it's easy to get confused about which stage a certain file belongs to, and accidentally mix up assets.

[ksec]

>I find it incredibly helpful to know that .jpg is lossy and .png is lossless.

Unfortunately we have been through this discussion and author of JPEG-XL strongly disagree with this. I understand where they are coming from, but for me I agree with you it would have been easier to have the two separated in naming and extensions.

[stavros]

But JPEG has a lossless mode as well. How do you distinguish between the two now?

This is an arbitrary distinction, for example then why do mp3 and ogg (vorbis) have different extensions? They're both lossy audio formats, so by that requirement, the extension should be the same.

Otherwise, we should distinguish between bitrates with different extensions, eg mp3128, mp3192, etc.

[crazygringo]

In theory JPEG has a lossless mode (in the standard), but it's not supported by most applications (not even libjpeg) so it might as well not exist. I've certainly never come across a lossless JPEG file in the wild.

Filenames also of course try to indicate technical compatibility as to what applications can open them, which is why .mp3 and .ogg are different -- although these days, extensions like .mkv and .mp4 tell you nothing about what's in them, or whether your video player can play a specific file.

At the end of the day it's just trying to achieve a good balance. Obviously including the specific bitrate in a file extension goes too far.

[nothrabannosir]

Legacy. It’s how things used to be done. Just like Unix permissions, shared filesystem, drive letters in the file system root, prefixing urls with the protocol, including security designators in the protocol name…

Be careful to ascribe reason to established common practices; it can lead to tunnel vision. Computing is filled with standards which are nothing more than “whatever the first guy came up with”.

https://en.wikipedia.org/wiki/Appeal_to_tradition

Just because metadata is useful doesn’t mean it needs to live in the filename.

[Ukv]

If the alternative was putting the information in some hypothetical file attribute with similar or greater level of support/availability (like for filtering across various search engines and file managers) then I'd agree there's no reason to keep it in the file extension in particular, but I feel the alternative here is just not really having it available in such a way at all (instead just an internal tag particular to the JXL format).

[account42]

> .png is lossless

pngquant and similar tools disagree

[jorvi]

Well yeah, you can turn any lossless format lossy by introducing an intermediate step that discards some amount of information. You can't practically turn a lossy format into a lossless format by introducing a lossless intermediate step.

Although, if you're purely speaking perceptually, magic like RAISR comes pretty close.

[basilgohar]

pngquant does the lossy conversion, not the PNG format.