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Decoding small QR codes by hand (2012)

311 点作者 terryds大约 2 年前

16 条评论

avian大约 2 年前
&gt; 99% of the QR codes you encounter don&#x27;t have any missing bits<p>I see a lot of cutesy QR codes out there that include a logo in the center.<p>These are basically intentionally damaged and depend on error correction to recover the missing bits that are covered by the logo.
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cyberax大约 2 年前
My pet peeve:<p>WTF PEOPLE ARE NOT PUTTING A CLEAR TEXT URL NEXT TO THE QR CRAP?!?!?<p>Especially when the QR code itself points to a URL shortener.
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rreichel03大约 2 年前
This is really neat! I’ve wanted to know the QR code contents a few times without actually scanning with my phone so I actually built a super simple app to do this. Nothing fancy, just dumping the raw contents of the code to a string.<p><a href="https:&#x2F;&#x2F;apps.apple.com&#x2F;us&#x2F;app&#x2F;barcode-qr-scanner-rawcode&#x2F;id1636758263" rel="nofollow">https:&#x2F;&#x2F;apps.apple.com&#x2F;us&#x2F;app&#x2F;barcode-qr-scanner-rawcode&#x2F;id1...</a><p>Happy to add any features folks might be interested in!
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xg15大约 2 年前
One thing that cleared up some confusion for me: The tattoo photo shows a version 2 QR code (as he writes) but the schematic images are for a version 1 code[1].<p>That&#x27;s also why the bottom right alignment pattern is missing in the schematics. He didn&#x27;t forget it, it&#x27;s just not there in a v1 code.<p>[1] <a href="https:&#x2F;&#x2F;www.qrcode.com&#x2F;en&#x2F;about&#x2F;version.html" rel="nofollow">https:&#x2F;&#x2F;www.qrcode.com&#x2F;en&#x2F;about&#x2F;version.html</a>
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jraph大约 2 年前
Scilabus made a nice video about it for French speaking people [1].<p>On a linux computer, I take a screenshot and run zbar, a cli tool available in the repositories.<p>[1] <a href="https:&#x2F;&#x2F;m.youtube.com&#x2F;watch?v=wKB-ZI2gXsk">https:&#x2F;&#x2F;m.youtube.com&#x2F;watch?v=wKB-ZI2gXsk</a>
matsemann大约 2 年前
How do camera apps recognize where the QR code is in the image, and what part of the image it should decode? I guess it also often has to some processing on it, as it will be scewed&#x2F;bent&#x2F;etc.<p>Looking at this guide, it&#x27;s easy to understand the steps. But I don&#x27;t get how one actually would apply them in code to a picture of a QR code. How?
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userbinator大约 2 年前
Regardless of what specification you&#x27;re implementing, I always recommend &quot;mentally executing&quot; the algorithms for at least small test cases, as when you inevitably need to debug your implementation, you will be forced to do so anyway, and it increases your familiarity with what it should be doing. As the saying goes: &quot;how can you tell the machine what to do, if you don&#x27;t know how to do it yourself?&quot;<p>For those who want to go the extra step and try the error correction by hand too, this article will be useful: <a href="https:&#x2F;&#x2F;en.wikiversity.org&#x2F;wiki&#x2F;Reed%E2%80%93Solomon_codes_for_coders" rel="nofollow">https:&#x2F;&#x2F;en.wikiversity.org&#x2F;wiki&#x2F;Reed%E2%80%93Solomon_codes_f...</a><p>(Side note: the example image of a QR tattoo evoked slight feelings of trypophobic disgust.)
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sandebert大约 2 年前
Somewhat related: How to recover a broken QR by hand. <a href="https:&#x2F;&#x2F;www.robertxiao.ca&#x2F;hacking&#x2F;ctf-writeup&#x2F;mma2015-qrcode&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.robertxiao.ca&#x2F;hacking&#x2F;ctf-writeup&#x2F;mma2015-qrcode...</a>
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teeray大约 2 年前
Can’t wait for someone to do this on a post-apocalyptic TV show
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omoikane大约 2 年前
Related, this page has a step by step process of how the encoding process works:<p><a href="https:&#x2F;&#x2F;www.nayuki.io&#x2F;page&#x2F;creating-a-qr-code-step-by-step" rel="nofollow">https:&#x2F;&#x2F;www.nayuki.io&#x2F;page&#x2F;creating-a-qr-code-step-by-step</a><p>Previously discussed here:<p>2020: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=24119124" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=24119124</a><p>2018: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=18360847" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=18360847</a>
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cornholio大约 2 年前
While I understand the teaching approach, this sound like the type of task which, even if it came up as a completely random one-off need, I would feel is much easier to solve in code. The inevitable bugs in my script are at least repeatable and I can iterate until I have a solution, whereas a single bit error in the manual process will waste the entire effort with no progress.<p>And experience has shown that, more often than not, such hack scripts find ways to grow into mission critical services. Sure, it&#x27;s an ancient Mayan qr code that is unique in the world and we just so happen to have found precise decoding instructions; but are you sure the one of the stone bits isn&#x27;t just a piece of fossilized bird poo that was not present in the original? Are you sure all the stone pieces were found? are you sure no other ancient qr codes will be found in the future?<p>Life is too short not to automate everthing.
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xg15大约 2 年前
Is there any reason why so many different masks are required and why the mask patterns are so elaborate? In particular the last few masks seem mostly designed to make life hard for (human) decoders :)
YuccaGloriosa大约 2 年前
The idea that the ability to decode could be lost makes me me wonder what info you would need as a kind of Rosett Rosetta stone for a future or alien civilization. I&#x27;m thinking what would you have on a wall of stone?<p>Would it be possible to represent the whole decode process with all options, and do it purely pictorially?
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nayuki大约 2 年前
Someone made a decoding video tutorial a decade ago: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=KA8hDldvfv0">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=KA8hDldvfv0</a>
stuckkeys大约 2 年前
Holly shit. How bored was this guy. Kudos for the dedication. Reminds of that silicon valley scene. How many guys they can j off. Funny shit.
tasuki大约 2 年前
Some weird comments there, eg:<p>&gt; I am stuck decoding a qr code.... I have tried several ways. It was sent a long time ago so maybe it has expired. Any takers?<p>I don&#x27;t think they read the post...