Question: maximum information density in the
print-scan process?
Does anybody know how much information can be stored and
reliably retrieved from a piece of paper, using a standard
printer (inkjet or laser, 300dpi) and a scanner (1200 dpi)?
Since a piece of paper can be affected by bit
rot (literally) and can be damaged in various ways, some
error correction (e.g. Reed Solomon) and detection (e.g.
CRC) is necessary. Also, I do not want to rely on
high-quality paper so I have to accept some ink diffusion
and “background noise” introduced by defects in the
paper.
I found some references to 2D
barcodes (such as DataMatrix,
PDF-417
and others) but these codes are designed to be scanned
efficiently by relatively cheap and fast CCD scanners. I am
not worried about the scanning time (I am using a flatbed
scanner) or the processing time (I can accept some heavy
image processing). Also, I would like to encode raw bits
and pack as much information as possible on a sheet of
paper, regardless of its size. These 2D barcodes have a
fixed or maximum symbol size and it is necessary to use
several of them if I want to fill a sheet of paper, wasting
space in the duplicated calibration areas and guard
areas.
PDF-417 has a maximum density of 106 bytes per square
centimeter (686 bytes per square inch, for you retrogrades),
which is quite low. It is certainly possible to do better,
but I would like to know if there are any standards for
doing that. I am especially interested in methods that are
in the public domain, because most 2D barcodes are patented
(e.g. PDF-417 is covered by US patent 5,243,655
and DataMatrix is covered by 4,939,354,
5,053,609
and 5,124,536).
If you know any good references, please post them in a
diary entry (I try to check the recent diaries once a day,
but I may miss some of them) or send them to me by e-mail:
quinet (at) gamers (dot) org. Thanks!
Hmmm… This is a bit long for a diary entry. But I
don’t think that such a question deserves an article in the
front page. If you think that I should I have posted this
as an article, then send me an e-mail and I will re-post
this question and edit it out of my diary.