Yeah, I've been looking for a guide to implementing qr readers from 0. Explicitly not 'oh just plug in this CV library in, feed it the image and it spits out the result' like all the stuff I find in Google on the topic.
I am looking for a guide that walks you through implementing all the algorithms necessary after you have the decoded raw image data.
find a copy of the standard. A version of it is floating online. The latest version just added some clarifications, but is not needed. I built an implementation out of that, though the error correction part, of course, I had to learn somewhere else. But the spec is very readable