PaperBack - proper way of storing information on paperSome 20 years ago I had an idea of storing data on paper - for backups and such. Never ended up implementing it. But luckily someone did - and since 2007 we've got PaperBack made by Oleh Yuschuk.
While playing with it I was able to store ~500 KiB of data on a single side of A4, which could already have some practical use. This density is achieved at 300dpi data density, 80% dot scale (recommended value of 70% gave higher error rate) and 20% for ECC correction. For reliable recovery scanned image had to be slightly sharpened using Gimp2/unsharp mask, but it feels like this is the limit (ECC had to recover ~10% of errors). On 200/240dpi data density everything is much more reliable.
One can for example take a photo of the sheet using film camera and get data microfilms at home ))) Also, this data is easy to read even in distant future and does not depend on spefic reading hardware, so even aliens or humans 1000 years in the future who find a timecapsure with it would be able to read it...
Here is how data looks at 80dpi:
Now data at 300dpi, maximum for 600dpi printer:
Even closer (square side is 2.97мм). One can see that using less than 2*2 pixels for 1 bit of data would require different recovery approach due to very high rate of errors which will be pattern-dependent. Paper fibers would also cause some issues as higher data densities.