How do QR codes dif­fer from bar­codes?

BBC Earth (Asia) - - Q&A -

Bar­codes come in all shapes and sizes. The first suc­cess­ful bar­code was the Uni­ver­sal Prod­uct Code (UPC), used for track­ing prod­ucts in stores, which en­codes 12 num­bers. Other bar­codes hold more in­for­ma­tion, for ex­am­ple the Royal Mail Mail­mark (TM) type L bar­code – which en­codes 26 char­ac­ters in­clud­ing ID, post­code and de­liv­ery point. QR codes are an­other kind of bar­code, and there are many sizes. A ver­sion 4 QR code is 33 x 33 pixels in size and en­codes up to 50 char­ac­ters. A ver­sion 40 QR code is 177 x 177 and stores 2,953 bytes, or up to 7,089 dig­its. This par­tic­u­lar QR code is so densely packed it looks like a pic­ture of a snow­storm, and is rarely used be­cause it’s dif­fi­cult to scan suc­cess­fully.

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