Not a film, something printable, that lasts without battery or can be put on a poster at a protest. At 3kB/in^2 in a 3x3 grid of barcodes you'd scan left-to-right, top-to-bottom, if the text itself were compressed with PPMd down to 25% of its original size, that 3x3 barcode grid gives you 108kB of text

or 12kB in a single barcode (of plain text, compressed down to 3)

wikipedia says: "Microsoft claims that laboratory tests using standard off-the-shelf printers and scanners have yielded readable eight-color HCCBs equivalent to approximately 3,500 characters per square inch"

so I'm being optimistic, but not wildly so

Here's some neat pics: https://www.microsoft.com/en-us/research/wp-content/uploads/...

https://www.microsoft.com/en-us/research/wp-content/uploads/...

I've read about this a bit and I really wish there were an unpatented color barcode and a reliable/fast open source reader also, even if it's not quite as dense as my dreams. I think it would make for some neat possibilities.

You can still generate them from a Microsoft site:

https://www.microsoft.com/tag/m/Make.htm

There are some phone apps in the wild still that will read and/or generate them.

At one point circa 2010 there was an https://tag.microsoft.com homepage for them, but trying it just now it doesn't seem to resolve any more.