Filtration Residue

horst · Post by **horst** » Thu Oct 01, 2009 10:37 am

I've extracted some information from the image but I have no clue what the solution is. Any hints?

michuber · Post by **michuber** » Fri Oct 02, 2009 2:44 pm

You should consider the first sentence of the last paragraph.

jonik555 · Post by **jonik555** » Thu Mar 11, 2010 5:54 pm

I'm really stuck here, I have extracted informations too, but i cant find the answer, do You mean last paragraph of informations in picture? (is that sentence this? Xxx xxxxxx xxx xxxxxx xxxxx xx xxxxx xxxxxx xxxxxxxxxx xx xxxxx xx x xxxxxxxx-xx-xxxxxxxx xxxxx.) or last paragraph in whole information(not only part inside picture). Please help me little bit.

michuber · Post by **michuber** » Thu Mar 11, 2010 9:00 pm

Did you compare the extracted text to the original?

teebee · Post by **teebee** » Thu Mar 11, 2010 9:01 pm

Yes, the crossed out sentence is the one pointed out by michuber. Moreover, you should read the excerpt carefully.

jonik555 · Post by **jonik555** » Fri Mar 12, 2010 6:18 am

Thank you, but I still dont understand this sentence. yes i compared it and found something added to table, but dont know what to do with it. what is the form of answer? and is the filter type the one used in IHDR header?

laz0r · Post by **laz0r** » Fri Mar 12, 2010 5:00 pm

Any help on how to extract the information in the first place?

jonik555 · Post by **jonik555** » Wed Mar 17, 2010 5:37 pm

Yes. I have got it! Many thanks for hints.

Adriano · Post by **Adriano** » Sat Oct 23, 2010 8:17 pm

That was a tricky one - and it brought me some deeper understanding of the PNG spec..

Thanks for the hints!

HugStuart · Post by **HugStuart** » Tue Oct 26, 2010 1:41 pm

Thank you all for this discussion. It helped a lot to solve this challenge. Once you are on the right track it's not that hard. I just wonder if there are some similiarities to "Lucy in the Sky with Briolettes"

michuber · Post by **michuber** » Tue Oct 26, 2010 2:50 pm

HugStuart wrote:I just wonder if there are some similiarities to "Lucy in the Sky with Briolettes"

This is a good hint for those who don't know the song.

MyNameIsAlreadyTaken · Fri Oct 29, 2010 12:16 pm

Alright, I'm pretty sure I'm on the right track [already decoded the first message], but for the next step i need to decompress the PNG-File.

From what I've understood in the PNG-specifications, I need to concat the content of all IDAT-chunks and it is decompressed using the LZ77-algorithm. The first step wasn't a big deal, but how can i decompress it now? I've tried to simply decompress it with gzip -d file.gz, but it didn't work.

Could maybe someone hint me on how to decompress the file?

Edit: Alright, my approach to try to convert the PNG-Data into a gzip file failed, since I don't know the crc32 of the original data. Fortunately, I got a hint via pm, that one of the tools I used had a nice option that wasn't documented in the manpages.

polarlemniscate · Post by **polarlemniscate** » Fri Oct 29, 2010 8:28 pm

Any hints as to which tool?

n
PostPosted: Fri Oct 29, 2010 12:16 pm Post subject:
Alright, I'm pretty sure I'm on the right track [already decoded the first message], but for the next step i need to decompress the PNG-File.

From what I've understood in the PNG-specifications, I need to concat the content of all IDAT-chunks and it is decompressed using the LZ77-algorithm. The first step wasn't a big deal, but how can i decompress it now? I've tried to simply decompress it with gzip -d file.gz, but it didn't work.

Could maybe someone hint me on how to decompress the file?

Edit: Alright, my approach to try to convert the PNG-Data into a gzip file failed, since I don't know the crc32 of the original data. Fortunately, I got a hint via pm, that one of the tools I used had a nice option that wasn't documented in the manpages.

MyNameIsAlreadyTaken · Fri Oct 29, 2010 9:09 pm

It was [tool removed, sorry guys], my manpages most seemingly weren't up-to-date.

I hope this isn't too much of a spoiler, it's just the tool - people will still need to think of what they got to do with the data.

laz0r · Post by **laz0r** » Wed Dec 08, 2010 1:23 pm

Ok, I've successfully decoded the message within and found a few differences within the table. However, do I need to consider all the random spacing and dots?