Re: How big could a bar code be if a bar code could be big?

From: Alan Dechert <alan_at_openvotingconsortium_dot_org>
Date: Fri Apr 30 2004 - 14:53:41 CDT


> In addition, however, my bigger question is this: how big can a bar code
> be? In other words, how many bits of stuff can we stuff into a maximally
> sized bar code?
The demo ballot has a barcode about 3 inches long. The data encoded is fits
in a 35-digit decimal number. We have to pad with a leading zero because
Code 128 char set C has digits in pairs. So, you could increase from 116
bits to however many more bits you could get from a 36-digit decimal without
increasing the length of the barcode at all. I'd guess you could go to a
50-digit decimal number without too much trouble (however many bits that
works out to be). This is all without compression. We discussed
compression some on this list and decided it wasn't needed for the demo and
some felt that it's best to avoid compression (better transparency).

I happen to feel compression would be okay. It's a trade off--transparency
versus economy. The number of bits encoded could be increased at least
three-fold (maybe ten?) with compression for a given length of barcode.

A 1-d barcode reader is really really cheap (negligible cost). 2-d not so
cheap (maybe $200)

> And is there a potential of mis-reads with such codes?

As discussed in this OCT thread, we added error detection code so that the
odds are astronomical against a mis-read that would be accepted as a valid
ballot (any misread would throw overvotes which our detection code would
see). That is, of the 2^116 possible numbers, only a infinitessimally small
percentage will constitute valid ballots.

This error detection method is stronger if we don't use compression. If we
use compression, this error detection method would not be quite as strong
but still pretty good.

So the long and short of it is that if without compression, a cheap 1-d
barcode reader might work for 150 bits-- with compression it could be
several times that.

Alan D.
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Received on Fri Apr 30 23:17:27 2004

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