From: Jim <jim.foltz@...>
Date: 2008-02-01T20:24:57+09:00
Subject: Re: Newbie: working with binary files/extract png from a binary file

On Jan 30, 7:29 pm, Adam Shelly <adam.she...@gmail.com> wrote:
>
>
> from the same docs:
> "MatchData acts as an array. ...  mtch[0] is equivalent to ... the
> entire matched string. "
>
> so m.begin(0) returns the offset of the start of the matched string
> (in this case, the start of the png header).  Since the string
> contains the contents of the whole file, the string offset is the same
> as the file offset we need.
> -Adam

OK, it's really not that hard is it?

input.read(N) read N bytes from the stream. From the spec we know PNG
has an header (they call a signature) that is 8 bytes. Check it. If
it's a PNG, read the chunks until IEND

The only other thing is unpack("N"). From the docs it takes a string
of 4 bytes and returns a Fixnum.

Thanks again for the code. The file I'm extracting is a SketchUp 3d
model, btw.