A look at QR Code resiliency – even when skewed, distorted, blurred and with up to a 30% chunk missing, QR codes can still be readable. The technology behind them is explained.
“The mask is applied via an XOR function and can be removed be applying the same Boolean operation a second time. There are multiple masks available in the standard that can be applied.
An additional alignment block appears in the fourth corner on small codes (in larger codes, multiple alignment blocks appear in the grid). These alignment blocks help deal with the skew. Finally, there are two timing strips in perpendicular directions composed of alternating elements.”