Decoding barcodes


Originally published at:


I saw something similar laid out in the 80s. As I recall, it wasn’t secret; it was pretty boring.



It sure is going to be expensive to barcode everyone…


We might have to cut corporate taxes even further so we can afford to pay for it.


I was bored one Saturday when I was 16 and figured out the encoding myself. The stuff about country codes and company codes was new and interesting to me though.


So, the key to understanding this secretive code is to…drink your SquareSpace?



I know it shouldn’t but the articles use of click bait thumbnail on main page really, really irked me.


This is interesting, but it’s just about UPC (or whatever it’s called nowadays). There are a lot of other barcode symbologies. Look at your mail; it has that USPS barcode, with the bars that always have a middle and might also have a top or a bottom. That replaces the old Postnet barcode, which encoded every digit of the ZIP code as a sequence of five bars, each either tall or short. There’s Code 39, which always starts and ends with an asterisk (or, as they say in Code 39, “narrow bar, wide space, narrow bar, narrow space, wide bar, narrow space, wide bar, narrow space, narrow bar”). There’s the very dense Interleaved Two of Five.

I could go on. But my point is just that, rather than “Decoding Barcodes”, the title should be “Decoding UPC Barcodes (episode 43 of the Decoding Barcodes series)”.


GS1. That’s it. There goes my grad school research.


You can download a barcode font if you need to print your own replacement library card, or so I hear from a friend.


Yes, if your library (like many) uses Code 39 and you know the sequence of characters encoded on your card. (It isn’t necessarily just the card number.) Code 39, unlike many symbologies (including, as the video linked here explains, UPC) has a sequence of bars to encode each character, so that the barcode for the whole string is just the barcode for each character, in sequence. And Code 39 doesn’t care how much space is between the last bar of one character and the first bar of the next, so you don’t have to worry about the character spacing that gets imposed on the string (over which, of course, the font designer has no control).

Hypothetically (though I bet it has never happened), a library could use the UPC symbology that this video discusses on its library cards. (They’d be using UPC’s system of encoding a 12-digit number as barcodes but not the rest of its system, which assigns every product a 12-digit number.) Such a library card could not be printed by a barcode font, since (as the video mentions) a different encoding system is used on each of the two halves of the UPC. (Though perhaps you could use two different fonts.)


I was disappointed he didn’t even talk about EAN-13 and its relationship to UPC-A.


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