I remember a couple of years ago I read up about the details on how QR codes are created. Specifically the masks that are added at the end to ensure that there aren’t any areas with too much whitespace or something that ends up inadvertently looking like the corner of a QR code (that square inside a square thing).
And for some reason, I’m staring at two QR codes in front of me, looking at the details, one looks like it contains a pipe going around a corner, another looks like it has a bit of a star, which made me wonder… Why have I never seen a QR Code with a swastika or something else you really don’t want to have on there? I’ve never seen any word on filtering out stuff like that when it comes to masking.
Am I just too bored out of my mind so that I’m staring at QR Codes like this with way too much imagination or is there something I’m missing?
EDIT: I’m sure it’s possible to intentionally create one, I’m thinking more of accidentally creating one. Specifically when I see, for instance, a different QR code on the back of every seat in a train, for instance - you’re generating so many, no human is going to check that.
Apparently there is a mechanism in the basic QR-code-generating algorithm that does something like this.
There are eight different patterns that can be used to display any given QR code’s data. All eight versions get generated internally by the generation software and then they’re assigned scores that penalize them based on various patterns:
- Large monochromatic blocks, anything more than 2x2 pixels of the same colour (white or black)
- Long lines of either colour
- Anything matching the “finder patterns” (the squares at the corners)
- Imbalance between 50% black and white pixels
The best one of the eight is the one that’s actually printed.
So a swastika isn’t explicitly searched for, but given that a swastika is composed of a bunch of long lines a QR code pattern like that would get penalized pretty harshly. The seven other QR codes would have to be even worse for it to slip through, and I bet the odds are pretty low for that.
Ah, so the same checks you need anyway to make sure the thing can actually be read – because a 2x2 vs 3x3 block might start to get hard to differentiate, for example – also happens to obviate OP’s issue as a coincidental side benefit.
QR codes can have arbitrary looks even without dirty tricks (abusing the error correction to add a logo or taking advantage of central sampling to color all but the middle 3x3 square of each data pixel) but boy, is it hard.
Examples:
https://lemmy.sdf.org/post/31694735/18805217 (strings a long number in Number mode (3 decimal digits per 10 bits) to the URL, and somehow the resulting number turns out to be a small even number times a very high power of 2)
https://www.youtube.com/watch?v=qQkWjzqMbuA (uses padding bytes plus maybe some of that “intentional damage” in QR codes with logos)OK, I was actually asking about accidental things, but this is pretty neat.
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Short answer, the masks would prevent them most of the time because they’re there exactly to prevent large blocks of continuous color as that would be difficult to recognize. Can you have small swastikas or other stuff in the middle? Yeah, but I don’t think anyone matters much about that. You can also purposefully create one but it will be hard to be read by a scanner and it’s likely going to be more random noise than anything useful.
Just wanted to say this is a fantastic question and the people who claim otherwise have bad reading comprehension
Do we upvote or downvote if we think its a stupid question how does this work?
Downvote content that is harmful to the community or instance, report additionally if it’s against the rules of either. Upvote good content and ignore the rest. Block whatever you feel like.
Though I suspect your question is more about what the community description means. Answer should be in there.
Yes feel the hate
You could probably intentionally create a qr code with a simple recognizable symbol, but it’d still necessarily have “clutter” around it which would make it stand out less. Also there are hard limits on the length of contiguous horizontal or vertical “lines”.
A qr code can have an arbitrary image embedded in it up to some limit, because remaining pixels are enough to decode it (perhaps there’s redundancy built in, idk for sure).
Most likely if you wanted to generate qr code that looks like swastika, you would have to input very specific letter nonesense to do it. Its very specific scenario and just pointless waste of manhours to prevent it, when someone who would want to generate such qr code would just do something else if prevented.
I’m sure it would be possible to do it on purpose, I’m thinking more of the scenario of a company pumping out thousands of different QR codes and one of them accidentally having something offensive on it.
Not a show, but The Martian, and soon Project Hail Mary
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