[ao98]

Wonderful write up, thank you! One question I’ve been trying to answer: I’ve been seeing more QR codes in the wild using dots instead of squares, and rounded edges instead of hard corners.

All my research suggests these are reader implementation specific and not guaranteed to work per the official spec.

But I find it hard to believe these codes are becoming more prevalent if they aren’t guaranteed to read.

Anyone have more info on this?

[kqr]

You'd be surprised how incompetent most adults are at what they do. I'm sure some less technical person assumed QR reading works the same way everywhere, tested it with their device and went "Yess it works! Ship it!"

I also sometimes see QR codes that are inverted. Not all readers detect them but many enough do that they end up in print.

[TonyTrapp]

That being said, the QR code readers most people have in their pockets already have to be able to deal with all sorts of problems (blurry pictures, dust on lens, and many more scenarios) that rounded corners are unlikely to have an affect on any of them.

[lights0123]

In reality,

- Apple's barcode reader

- Google's ML Kit

- and ZXing, probably behind most third party QR code scanning apps

covers most QR code readers that users will actually use, so testing them is fairly easy.

[Isamu]

Rounded corners is handled similarly to blurry images, one of the main ideas is readers to be forgiving in what they accept, and rely on the error detection bits to tell if it is way off. With error correction you can tolerate stylistic mangling.

[jillesvangurp]

The qr code scanning algorithm works based on contrast and is designed to work with poor cameras under poor light conditions. Whatever shapes, colors and shades are used are interpreted as either black or white squares.

The process starts by scanning for the 3 markers on the corners. That give you the square containing the qr content and it's orientation. The next jobs are figuring out the resolution of the square and the version of the qr code used. Eventually you end up knowing the grid dimensions. And then you simply scan the grid as the article outlines by simply averaging the pixels in each grid square to be "white" or "black". As long as you have enough contrast, most grid squares will scan correctly.

You can abuse this quite a bit before it starts breaking. There are some interesting QR codes out there that are barely recognizable as QR codes for people. But if you open them in an image editor and play with the levels and contrast a bit, they are obviously qr codes. And there's error correction too so it's OK if some of the qr code is scanned incorrectly.