Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Reading QR codes without a computer

qr.blinry.org

Post reply on HN
Print view View original

41–50 of 93 posts

Re: Reading QR codes without a computer

#41

Post by londons_explore »

Retr0id wrote: post #26
londons_explore wrote: post #21

Earlier quoted context omitted.

The 'proper' fix is to either engineer cameras that can focus closer, or to engineer barcode scanning apps to be able to see a code which is small somewhere in the frame. I think people are working on both as we speak.

It doesn't matter how objectively good your camera/decoder is, in absolute terms. There will always be some minimum size or maximum distance, where the detail can no longer be resolved (or errors no longer corrected)

If we're talking theory, the pixel size doesn't matter - it's the amount of information encoded in the QR code that matters (ie. excluding ECC bits!). In turn, that means it is theoretically possible to decode a QR code where each 'pixel' of the code is smaller than the pixel of the camera sensor observing the code.

While it is theoretically possible, nobody has yet done so...

Re: Reading QR codes without a computer

#44

Post by RugnirViking »

Aachen wrote: post #37
RugnirViking wrote: post #10

Earlier quoted context omitted.

Last year I did some experimentation along these lines and I also found that no error correction was best, at least when 3d printing QR codes. I was trying to find how small I could print it and still have it be detectable. Like the sibling comment, I suspect it is because of individually larger pixels.

The problem with that, as I understand it, is that your 3d print (or any print or screen) cannot get damaged at all. The pixels being bigger makes it easier to scan ...when it's fully in view and fully intact. Any pixel fails, and you can never recover the original data (besides some guesses, e.g. if the protocol identifier gets damaged a la htwps://) Error correction doesn't seem to be for easier scanning, but for e…

the idea that a single pixel of the design would get damaged absent the rest seems unlikely. What seems to be more common is that a direction of light/some flaw in the printing process causes many/all pixels to be flawed in the same way past some threshold.

Re: Reading QR codes without a computer

#45

Post by bluGill »

mr_mitm wrote: post #27
bluGill wrote: post #23

Earlier quoted context omitted.

It would probably only take a week of training/practice for someone to get good enough to read them manually. Particularity if the vaccination codes have a common pattern - the same mask, format information and the like. I would expect you can look at a few areas to see if the person is vaccinated (though this wouldn't pick up on someone else's vaccinated status)

There is a digital signature embedded in the QR code. No one can verify that in their head.

We don't need to verify everything though, just extract the vaccinated/not field which is probably in the same location on every QR code (or at least it should be possible to make it in the same area), and maybe the name of the person the QR code is for.

Re: Reading QR codes without a computer

#46

Post by epcoa »

andirk wrote: post #20
ajsnigrutin wrote: post #9

> So is the rest all content? Not quite! There is also error correction, which is used to make sure that the QR code can still be read even if some parts are damaged, blurry, or missing. The error correction is generated by some fancy math, and we don't care about it here for the purpose of reading it by hand. This should be explained better... I mean sure, the math can be hard.. but is the error correction appended…

Barcodes use the last digit as a checksum. The checksum is some adding up the numbers and multiplying or something, then % 10 (only 0-9 possible values). As you can see with this math, the error checking has a 1/10 of a chance of coincidentally showing a correct checksum in cases where the data is incorrect. Either way, that last digit on barcodes is insignificant to the actual product's unique barcode ID. Fun story:…

A few common barcodes including UPC work this way but mostly this is the exception. The 2D ones being discussed here like QR and Aztec use actual error correcting codes, so none of them. In the linear space Codabar (libraries) is a widely used example that doesn’t. GS-128 doesn’t, etc.

Re: Reading QR codes without a computer

#47

Post by cyco130 »

efdee wrote: post #24
cyco130 wrote: post #5

Slightly off topic: One day in the late 90s or early 2000s, I wanted to transfer the contents of my Atari 8-bit disks to my PC. I did know about SIO2PC, a cable that converts between Atari's SIO port and the PC's serial port and a piece of software to go with it. But I didn't have the electronics skills to build one (even though it is actually very easy). So I ended up writing a Basic program on the Atari to read dat…

Just wanted to say this sounds like a fun project and you must have been pretty happy when it ended up working out!

I was so happy that I'm still boasting about it some 25 years later!
Post reply on HN