Hacker News Reader

> Compared to other QR designs, this does not take advantage of error correction that QR codes use, but rather deterministically turns some pixels in the code pattern on or off without affecting what the QR code is pointing to.

Can someone explain how this is done? Is it adding characters to the URL that somehow browsers will ignore?

View on HN

I assume there's a bit more to it, but QR codes inherently support a "mask" that tells the scanner parts of the image to ignore. So you could do at least some of that with the mask. It's not real flexible, so there's perhaps other tricks also.

I was under the assumption that the mask was just a short static pattern XORd over the data?

It is, the QR code spec details a few specific masks that are available. The one which produces the best QR code is chosen (best in this case means most clear/easiest for a scanner to read. So, no large blocks of white or black).

Wikipedia has a pretty good visual of this. https://en.m.wikipedia.org/wiki/QR_code#Encoding

Reply on news.ycombinator.com