Ask HN: How are QR scanners written?

10 points by mdoms 4y ago ↗ HN

I have been programming web and backend stuff for over a decade but I have never done any kind of image processing. I tried googling but there is so much noise in the QR space.

What I want to know is, how does QR scanner code work? How do you go from a photo of a QR to the encoded text within, allowing for all of the factors that will get in the way like poor quality cameras, off-center photos, blurriness etc? Is there a code-first tutorial or worked example somewhere?

3 comments

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gt565k 4y ago ↗

https://www.explainthatstuff.com/how-data-matrix-codes-work....

muzani 4y ago ↗

Here's some code you can dig into: https://github.com/zxing/zxing

It's a very good one, and one that has been copied for a lot of custom QR scanners

pavelgvay 4y ago ↗

On my first job at an internet provider company, they had no backend. They were using some proprietary software and SQL functions instead. One day the CEO came in and said: "Guys, we need to print a small QR code on mails to customers. ". The team lead responded: "Sure, our intern can do it."

Oh my gosh, that was a crazy task! I built a fully functional QR code generator on pure SQL from scratch! It was very fun.

Check out Wikipedia [1]. They explain how QR codes work really well. Well enough to build your own generator.

I also used ZXing code [2], that Muzani shared below here, as a reference.

[1] — https://en.wikipedia.org/wiki/QR_code

[2] — https://github.com/zxing/zxing