[midjji]

I'm really not a fan of using the generally unsupported aspects of the file formats. Like sure, png supports alternate compression schemes which in combination with the fully generic datablocks system which I think technically accidentally makes it Turing complete. But its not like any reader ever supports it fully, hell most readers dont support showing the other images in a png file. Its also quite common that palettes aren't properly supported, in particular for uncommon combination. Palettes themselves are also not truly sufficient for what they are supposed to do, as that would require generic scalar to scalar functions. Its like this with every damned old image format. People try to make the format to end all formats and end up accidentally inventing really shitty programming languages with terrible separation of concerns which are terribly supported but work as people only ever use them for single image data.

Another stranger mistake is the use of generic compression a part of the format, its much better to leave that up to the filesystem or stream. I dont really understand why this was ever a good idea, but it certainly hasn't been one for decades.

The more recent blob formats people have developed aren't much better, they still confuse the specification of a single blob with the specification of the container format, and try to be convenient and fully generic at once. If people actually wanted a fully generic dataformat and accepted that this requires a programming language, just let that be python, instead of inventing some shitty new one...

[spider-mario]

> But its not like any reader ever supports it fully, hell most readers dont support showing the other images in a png file.

Do you mean APNG? In all fairness, that is not even in the specification although there is discussion to add it. https://github.com/w3c/PNG-spec/issues/26

The one that was specified was MNG but it was a different format and practically no one used it since it was not parsable as a PNG.

[midjji]

No not animated, I mean that the .png format specifies how to specify an arbitrary number of datablocks, without specifying how they should be used aside from amounts to an recommendation of which one should be shown.

It used by some videogames as assets, for instance storing what amounts as a thumbnail as a shown image, but leaving meshes and textures in the other internal datablocks.

[ErikCorry]

I think I don't understand what you mean by an AR encoder

[midjji]

Its auto regression. Think of a row of pixels as a signal y[n]. Assume y[n] = a y[n-1] + b y[n-2]. estimate a,b. Then store y[0], y[1], a, b, and the residual, then encode the four values and the residual which will mostly be zeros. You can vary the length and number of coefficients very cheaply, but a fixed two beat png in my tests. There are fast standard algorithms to find a,b and which along with some simple tricks to correct for the precision ensure lossless encoding. Its the mathematicians version of the ad hoc thing png tries to do.