this post was submitted on 07 May 2022
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Asklemmy
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There are many types of QR code. iirc a single qrcode can contain up to a few kilobytes, but the more data you put in it the more difficult it will be to scan.
so, you could use qrcodes for offline distribution of short text messages or very low resolution images. I think mobile devices' qrcode scanners will display the contents of TEXT type qrcodes, but they probably don't have support for decoding an image from one (so such an app would need to be written). you can create TEXT type qrcodes using the
qrencodetool (packaged in major linux distros) or using websites like https://www.qr-code-generator.com/ (note that I think only their URL and TEXT types are offline; the others upload a file to their servers and make a qrcode containing a URL for it).This qrcode says "Hello":
This qrcode contains this 88x26 pixel (1467 byte) image:
(created using
cat lemmy.png |base64 |qrencode -o lemmy_qr.png; can be decoded usingzbarimg lemmy_qr.png |sed 's/QR-Code://'|base64 -d > output.png. on debian/ubuntu you canapt install qrencode zbar-toolsto get the two required commands.)I didn't know there was an actual limit to the size of a QR code, but as we see a big problem with (raster) images is that the QR code rapidly becomes much more complex than the image itself
Vector images can be a good fit though! If you can fit a URL in there, a SVG could fit in too :)
I agreed a priori, which, as you probably guessed, is exactly why I put that parenthesis π But I think in practice the starting point already is too complex. For example, I opened inkscape and saved the empty image, the result is already more than 1KB. Similarly, Lemmy's very simple logo is already 3KB.
SVGs can be minified after edition, but of course nothing will beat hand-crafted SVGs...
Thanks for the clarification ! This indeed makes the code readable, although way more complex than the original logo. Also, not everyone has an app able to read that svg on their smartphone
Yep. It's another advantage of Vector Graphics.
Awesome! Thanks for the in depth response and examples.
I'll have to see if I can successfully decode your lemmy picture when I get home to my computer.
I learned alot today! Unfortunately I also learned that there are no 'QR codes' that can achieve the scope of what i wanted. π
If it doesn't exist, then you can invent it.
QR codes are perfect for encoding text, even though most people just use them to send URLs. It should be a very good tool for flyers.
If you want rich text, colours and fonts and sizes, I'm sure that's easy too. But you might need to invent a type of markup to compress the style information better. Or it might already exist.
That's just it though, it is very limited and has issues with even simple text. Tryp said in this thread that they had to download additional stuff in order to display the text in a QR code.
I had similar issues when scanning a text QR Code. Being a QR code, it opened my browser... Simple text was displayed in my search bar in linear fashion. So basic formatting of text to make an ASCII bar graph, for example is not possible.
Without basic formatting capabilities it's almost useless for my purpose, unfortunately.
This is very much a problem with the app you use to scan rather than with the QR code itself.
Do all QR code phone apps do that, or just the one? Maybe it's a setting in the app that you can turn off. You'd think the app would be clever enough to recognise whether the message is a URL or not, and treat it appropriately.
QR codes can often be ticket numbers or lists of information. It's literally just text, but in a machine-readable form, instead of human-readable.
What did you want to do?
Think of a one-page flyer/poster JPEG that has textual information but also some bar graphs or pie charts to convey statistical information but discreetly disguised as a QR code.
All of the data would be contained in the QR code. This way it could work indefinitely... Rather than the QR code containing a URL and loading up a website so you don't have to worry about the website going offline or being censored. Not to mention websites can be tracked back to the owner. There are digital footprints.
It appears that QR codes can do very limited textual information, but nothing to the scope of what I need.
From personal experience, the Cowboy Bebop opening text (around 700 characters) is the most I could fit on a QR code while still being able to print it and scan it with my phone, in case that helps.
What do you mean the opening text? Like the credits? All the animator names and stuff?
That is a decent amount of info. My issues so far has been the formatting of the text.
I downloaded a new camera app that is geared towards QR scanning. Someone suggested it in this thread. Perhaps it would have better results and fewer issues with formatting.
Thanks for the info!
I just read about the error correction in QRCode; that's pretty clever. Could an oppressed class obscure QRCodes enough to hide information from the oppressors while still communicating information?
you're looking for steganography; I'm not aware of any steganographic constructions involving qrcodes, but there could be some. generally speaking, stego becomes practical in settings where there is unimportant high-entropy data which can be replaced with an encoding of the (typically encrypted) hidden message without altering the "cover" message in a detectable way. it might seem like this is the case with qrcodes due to the error correction; if you change a few random parts of the qrcode, due to the error correction it might still decode properly. However, this is probably easily detectable if the adversary has a high-resolution image of a candidate "maybe stego" qrcode: if decoding and re-encoding it produces a different qrcode, that would indicate that there had been extra data hidden in the error correction. (or, using a more advanced decoder than the typical ones, they could also simply see what the error rate is.)