[azinman2]

It literally stands for "FLIF - Free Lossless Image Format", and the first sentence is "FLIF is a novel lossless image format which outperforms PNG, lossless WebP, lossless BPG, lossless JPEG2000, and lossless JPEG XR in terms of compression ratio."

Seems like they're doing a pretty decent job at communication it's lossless to me.

[kragen]

It would be reasonable to interpret the shorter boast as making the very surprising claim that it beats anything else, including lossy JPEG, in all categories of performance, including compression ratio. As it turns out, they don't intend to claim that, because it's not true. It's probably impossible for a lossless file format to do that, even for commonly occurring images. (It's certainly possible for a lossless image format to do that for images that have a lot of redundancy in a form that JPEG isn't sophisticated enough to recognize.)

[monktastic1]

Surely nobody could interpret this as beating an arbitrarily lossy format. I could just erase the entire input, after all. One would have to incorporate quality into the metric. Because of that, it seems natural to assume they mean lossless.

[playpause]

If a given lossy format is inefficient enough, then it’s possible for a lossless format to beat it at compression. I initially interpreted the website as making the surprising claim that FLIF beats several popular lossy formats while itself being lossless. Most people understand “JPEG” to mean the popular lossy format, JPEG. The site could be a lot clearer that that they are actually comparing it to lossless JPEG, lossless WEBP, etc.

[lisper]

> It's probably impossible for a lossless file format to do that, even for commonly occurring images.

It's actually provably impossible using a simple counting argument. A lossy algorithm can conflate two non-identical images and encode them the same way while a lossless algorithm can't, so on average the output of a lossless algorithm is necessarily larger than a lossy one because it has to encode more possible outputs.

[kragen]

Yes, of course it's impossible to losslessly compress all possible images by even a single bit. But how predictable is the content of typical images? How much structure do they have? They certainly have a lot more structure than PNG or even JPEG exploits. Some of the “loss” of lossy JPEG is just random sensor noise, which places a lower bound on the size of a losslessly compressed image, but we have no idea how much.

[lisper]

Doesn't matter. Whatever you do to compress losslessly you can always do better if you're allowed to discard information. And the structure is part of the reason. For lossless compression you have to keep all the noise, all the invisible details. With lossy compression you're allowed to discard all that.

[kragen]

Yes, that's what I said.

[lisper]

Just for the record: https://news.ycombinator.com/item?id=22272837

[Dylan16807]

You should take more time before you start throwing out terms like "provably impossible". A sufficiently bad lossy algorithm can be worse than an algorithm like PNG in every single case. For example, a format based on PPM that can lossily reduce the file size by up to half.

[lisper]

> A sufficiently bad lossy algorithm can be worse than an algorithm like PNG in every single case.

Well, yeah, obviously if you want to shoot yourself in the foot that is always possible. But for any lossless algorithm it is trivial to derive a corresponding lossy algorithm that will compress better than the lossless one.

[Dylan16807]

> derive a corresponding lossy algorithm that will compress better than the lossless one

Which is a completely different problem from taking a fixed lossy algorithm and trying to beat it.

[lisper]

Fair enough. Nonetheless, a lossy compression algorithm by definition produces fewer possible outputs than possible inputs. A lossless compression algorithm, again by definition, produces exactly as many different outputs as there are possible inputs. Therefore, on average, unless the lossless algorithm has a perverse encoding that uses more bits than necessary to encode the possible outputs, no lossless algorithm can beat it on average. It is of course possible that a lossless algorithm might beat a lossy one on some select inputs. It's even possible that those inputs are the ones you are interested in, but in that case you are using the wrong lossy algorithm.

[ehsankia]

If we're going to switch to a new format, it would preferably support and be good at everything, including animation, lossy, alpha, metadata and color profiles.

What the first graph shows me is that this format is slightly better than WebP in one aspect, ignoring half the other features of it. Considering WebP is already far more ahead in terms of adoption, I'm happy sticking with that instead. It's natively supported in most browser and many graphics softwares, which is the real uphill battle for a new file format.

[lazyjeff]

WebP only needs Safari browser support before it's officially supported by all modern browsers.