Ippopotamus

What to call PNG/JNG/MNG/ANG?

Hi Ippopotamus–

Thanks for your clarification on PNG not being a container format!

I’m not clear on the precise terminology – what would one call the PNG file structure (chunks), as used in PNG/JNG/MNG/ANG? A container format? A wrapper format? A metafile format? AFAIK, “bitstream” is usually used for the raw data, right? —Nils von Barth (nbarth) (talk) 16:28, 22 April 2009 (UTC)

I think we should be careful with the term "container" as it can be easily devalued; technically, any file could be considered as a container because it "contains" something.

I would define "container" as a format which designed primarily to keep some data which a) have its own format specification not included in the container format specification and b) have some use outside the container or inside another container. In case of PNG we have critical IHDR/PLTE/IDAT chunks which a) described in the PNG specification b) have no meaning outside a PNG stream c) being absent, make the PNG stream meaningless. Any custom chunk that you could include in a PNG file is actually metadata which does not change the image stored in that file.

So PNG format is flexible and modular, but I believe it should not be called "container" only for the sake of to be called somehow.

As for the "stream"/"file" misconception: PNG data do not need to be stored in files as they do not include file pointers and can be read byte-by-byte without seeking back and forth; moreover, they can be included in another streams or files (Windows ICO, for example). So I find the term "stream" to be more appropriate but do not object against the "file".

—Ippopotamus (talk) 13:28, 23 April 2009 (UTC)

Thanks for the clarification – “Storage layer only – doesn’t define coding” seems a good way to put it.

It’s a similar design concept (forward-compatible storage layer vs. abstract storage layer), so I’ve made a note, but clarified that it’s not a container format.

…and thanks for the stream/file distinction!

—Nils von Barth (nbarth) (talk) 15:45, 23 April 2009 (UTC)

Yes, now it looks better —Ippopotamus (talk) 20:20, 23 April 2009 (UTC)