Twisted Zebras

MerickOWA · Post by **MerickOWA** » Fri Jan 30, 2009 12:55 am

I would like to thank fridolin for the barcode challenge. It wasn't until i searched on what kind of barcode his challenge was that i noticed QR code and recognized the 3 squares.

I thought this was some kinda odd folding of bits with xoring challenge

fridolin · Post by **fridolin** » Fri Jan 30, 2009 11:40 am

I'm glad my challenge pleased you

Unfortunately it's easily solvable by using some online-decoder. Decoding it manually or writing some decoding application is really more sophisticated, especially finding out how to converse the 4-17-modules to integer.

gfoot · Post by **gfoot** » Fri Jan 30, 2009 7:01 pm

I had trouble finding any libraries to decode them that weren't written for mobile phones, and didn't find anything online either. I found a library that did seem portable, installed its Python version, ran it, and got gobbledegook out. So I guess that library just doesn't work!

I actually solved it by getting a friend with an iPhone to take a photo of my monitor and decode it on that.

MerickOWA · Post by **MerickOWA** » Fri Jan 30, 2009 7:23 pm

Doh. You probably found the zxing decoder on google code. Theres a link to the "experimental online decoder" and you just have to give it the url of hacker.org's image.

Normally I like to reverse engineer these kinda projects and figure out the algorithm they're using, but after seeing the code for PDF419's barcode reader (I got lost in the error correction and code word conversion) I didn't even bother with this one

fridolin · Post by **fridolin** » Fri Jan 30, 2009 10:25 pm

This one works very well for example, linked via the German Wikipedia article about PDF417: http://turbulence.org/Works/swipe/barcode.html

Error correction doesn't really matter for this challenge - you can see it just as a kind of padding at the end of the code. But maybe this would be another interestion one - restoring a barcode from partially destroyed data

As i already wrote the most difficult part for me during my experimentations with PDF417 was finding out the conversion of the 4-17-modules to the integers. Maybe you will find the used tables interesting availabile as a zip file here: http://grandzebu.net/informatique/codba ... tables.zip

MichaBln · Post by **MichaBln** » Wed Feb 04, 2009 11:38 am

@ fridolin

You got the wrong topic you just posted pretty much the solution for "Barcode" in under "Twisted Zebras" topic ... its not that crucial since the solution is pretty much the same: Wikipedia/Google.

Anyways ... Schwamm drüber

fridolin · Post by **fridolin** » Wed Feb 04, 2009 11:59 am

Damn - you are right

Maybe someone could remove it...

MerickOWA · Post by **MerickOWA** » Wed Feb 04, 2009 3:32 pm

Probably my fault, I posted about the barcode challenge helping me solve this (the twisted zebra) challenge, since I figured that it was obvious that the barcode challenge was well ... a barcode, and I didn't want to give away the twisted zebra challenge to anyone who didn't know.

I had no idea that twisted zebra challenge was also a barcode until I googled barcodes and saw a picture of one and noticed the 3 alignment squares.

MichaBln · Post by **MichaBln** » Wed Feb 04, 2009 5:12 pm

Well ... since its really just googeling and finding an online-decoder its not relly that spoiling ! The challenges are pretty much the same in difficulty and approach. Another interesting question is why barcode is a MISC-Challenge while Twisted Zebras is not ... maybe its becaus one needs to figure out what that Twisted-Zebra-Barcode is.

moose · Post by **moose** » Tue Jul 12, 2011 7:02 pm

I've done it with Python:

Code: Select all

#!/usr/bin/python
from sys import argv
import zbar
import Image

if len(argv) < 2: exit(1)

# create a reader
scanner = zbar.ImageScanner()

# configure the reader
scanner.parse_config('enable')

# obtain image data
pil = Image.open('/home/moose/bar.png').convert('L')
width, height = pil.size
raw = pil.tostring()

# wrap image data
image = zbar.Image(width, height, 'Y800', raw)

# scan the image for barcodes
scanner.scan(image)

# extract results
for symbol in image:
    # do something useful with results
    print 'decoded', symbol.type, 'symbol', '"%s"' % symbol.data

# clean up
del(image)

Mon Jun 18, 2012 11:20 pm

All this time I thought, "Why is there no QR code challenge?"
...Whoomp, there it is!

aurora · Post by **aurora** » Sat Mar 16, 2013 5:55 pm

This one was a little bit too easy with "qrafter" on my iphone

...

Mon Mar 18, 2013 8:37 am

Agree about the easiness part. This challenge should open up way earlier.

michuber · Post by **michuber** » Mon Mar 18, 2013 3:20 pm

aurora wrote:This one was a little bit too easy with "qrafter" on my iphone ...

In 2008 QR codes were not that popular, so then it was harder...

Anyway, in 5 years Siri will solve the "Say It" challenge in seconds

aurora · Post by **aurora** » Mon Mar 18, 2013 3:51 pm

michuber wrote:
aurora wrote:This one was a little bit too easy with "qrafter" on my iphone ...
In 2008 QR codes were not that popular, so then it was harder...

Anyway, in 5 years Siri will solve the "Say It" challenge in seconds

yes, it's fascinating to see where we get with all this technology over time and i am almost sure you are right regarding "say it" and siri ... (damn, why is time-traveling not possible, yet?