Did you ever watch Star Wars and wondered how people understood what R2D2 was saying? Maybe [Luke Skywalker] would enjoy learning to decode QR Codes by hand, too. While it might not be very practical, it would be a good party trick — assuming, like us, you party with nerds.
You can start by scanning a code, or the site will create one according to your specifications or generate one randomly. It then takes the selected code and shows you how it is put together. Fun fact: 21×21 “modules” (QR-speak for pixels) is the size of a version 1 QR code. Each version increases the size by four modules.
You probably figured out already that the three big blocks in the corners are to help scanners find the code and orient themselves. There are also empty areas around the boxes that don’t count. Some versions of QR have additional patterns for alignment and timing bars that provide alternating bits.
As you might expect, other areas encode the format and error-correcting codes. However, one of the most important things is the mask. The mask pattern breaks up large areas of 1s or 0s. There are eight different masks, and since the goal is to do this all from memory, the site offers a helpful story about going to jail to help you memorize the different patterns. If you just can’t remember, they also offer you a foldable cheatsheet. Each black module in the mask inverts the QR code data.
Perhaps the hardest part is the actual reading, which zig-zags in two-column groups. You might also want an ASCII cheat sheet, although we ..
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