❯ Guillaume Laforge

Decoding a QR code by hand

Doing sport at home on a treadmill or an elliptical bike is pretty boring, when you’re confined, so to make things more interesting, I’m watching some videos to learn something new while exercising. This time, I found this old video about how to decode QR codes… by hand! Have you ever thought how these were encoded?

This video comes from the Robomatics YouTube channel. You recognise easily QR codes thanks to the 3 big squares with the inner white line. I knew about the purple dotted lines that was fixed in those patterns. What I didn’t know however was that there’s a mask that is applied to the data, to avoid QR codes to potentially look all white or black. It was interesting to see also how the bytes were encoded: how they follow a path through out the matrix.

However, what this video doesn’t cover, for example, is how error correction is working. You might have some holes or a bad picture of a QR code, but still being able to decode it with some level of loss of data. So I’ll have to learn how that part works some day!