Storing compressed alphanumeric string in QR Code

Question

I'm working on storing a JSON snippet onto a type 31 QR Code so that I can scan it with a smartphone and parse the JSON.

I'm running into a few challenges..

A type 31 QR Code is the "densest" (for lack of better words) code that I can get my Android device to reliably scan. This can store 2677 Alphanumeric characters factoring in 7% error correction.

What are my options for compressing my optimized/minified JSON object and encoding a QR code with it? Conceivably, how much more data can I store? Or am I even barking up the right tree?

Answer 1

It all depends, really.

1. Is Wi-Fi available? If so, put your JSON snippets on a web server and encode their URLs in the QR codes. Problem solved.

2. If this is for general consumption, then you need to be aware that some phones are better than others. Mine really struggled to scan a version 25 QR code. I'd consider anything higher than version 20 as unreliable.

3. There's little benefit in using the alphanumeric mode. It only stores uppercase letters, digits 0-9 and a handful of punctuation marks. At 5½ bits per character (11 bits per pair), its storage capacity is almost identical to the corresponding binary mode (8 bits per character).

4. In a quick test gzip -n -9 reduced a 545-byte JSON file to 219 bytes (40% of the original size). You could do a lot better than this if you stored your data in a compact binary format instead of a verbose tagged format.

5. If you're putting these QR codes out in public, you'll need to include some sort of authentication mechanism (e.g., a 32-bit checksum) to prevent malicious code injections and other tomfoolery.