Filtration Residue

smutley · Post by **smutley** » Thu Jul 22, 2010 6:04 pm

I loved this challenge. I learnt so much more about the PNG format and I thought that the idea was brilliant. Kudos to teebee - it must have taken ages to create.

teebee · Post by **teebee** » Sun Jul 25, 2010 6:41 pm

Thanks, I am pleased that you enjoyed the challenge. To create the image I patched `pngtest.c' and `pngwutil.c' of the libpng library (http://www.libpng.org/pub/png/) which wasn't such difficult.

Using `pngcheck' and `perl' the challenge can be solved in one line as follows:

Code: Select all

pngcheck -vv residue.png | perl -ne 'if ($a) { $a = 0; push @a, map { $_ + 0 } split /\s+/, $1 if /^\s+((\d\s)*\d)/ } else { $a = 1 if /row filter/ } END { print"@a" }' | perl -lne 'BEGIN { %a = (0, "11", 1, "010", 2, "011", 3, "10", 4, "00") } $a .= join "", map { $a{$_+0} } split /\s+/; END { print map {chr} map { eval '"'"'$_ = 0b'"'"'.$_ } $a =~ /.{8}/g }'

bsguedes · Post by **bsguedes** » Fri Sep 02, 2011 7:53 am

teebee wrote:Thanks, I am pleased that you enjoyed the challenge. To create the image I patched `pngtest.c' and `pngwutil.c' of the libpng library (http://www.libpng.org/pub/png/) which wasn't such difficult.

Using `pngcheck' and `perl' the challenge can be solved in one line as follows:
Code: Select all
pngcheck -vv residue.png | perl -ne 'if ($a) { $a = 0; push @a, map { $_ + 0 } split /\s+/, $1 if /^\s+((\d\s)*\d)/ } else { $a = 1 if /row filter/ } END { print"@a" }' | perl -lne 'BEGIN { %a = (0, "11", 1, "010", 2, "011", 3, "10", 4, "00") } $a .= join "", map { $a{$_+0} } split /\s+/; END { print map {chr} map { eval '"'"'$_ = 0b'"'"'.$_ } $a =~ /.{8}/g }'

You still have to google the guy's last name to solve the challenge

Nice challenge, PNG images really offer a lot of possibilities to hide information in them.

SnakeSnake · Post by **SnakeSnake** » Thu Sep 22, 2011 10:52 pm

Of course after writing my own png reader with C/zlib I have to see here that pngcheck can display the filters too...

Anyway nice challenge I enjoyed it alot!

Mon Jun 25, 2012 4:51 pm

Nice challenge. Why did it take me so long to stumble upon pngcheck

helly0d · Post by **helly0d** » Thu Jan 28, 2016 6:20 pm

Nice challenge. Nice one teebee.

Hippo · Post by **Hippo** » Sat Jan 30, 2016 9:47 pm

helly0d wrote:Nice challenge. Nice one teebee.

Yep, definitely. This one was teaching.

Hckr · Post by **Hckr** » Wed Aug 23, 2017 10:11 am

Awesome challenge teebee. It was as if you told a little story there.