Exactly as I figured - which is why I wanted to see the PDFs.

Whatever software is producing the PDF is drawing a filled white opaque 
rectangle the size of the paper/page as the first thing it does.  Here's the 
start of the content stream (bold & red are mine for emphasis) of Note-14-49:
q
1 1 1 rg /Gs1 gs
0 792 612 -792 re f
0.2 0.2 0.8 RG 0.85 w
1 J
1 j
[] 0.0 d
10 M 188.625 705.937 m 188.625 706.652 l 187.906 706.652 l 187.191 707.371 l

So what you need to do is get the original authoring software (which appears to 
be using Cairo) to stop that - and just write out the S's.  I manually removed 
them from out-merge and enclosed the result.

Leonard

From: Matthew Chan [mailto:[email protected]]
Sent: Sunday, April 24, 2011 3:00 PM
To: Leonard Rosenthol
Cc: [email protected]
Subject: Re: [Podofo-users] transparent overlap of PDF

Hi Leonard,

Thanks for your reply.

I might have been a bit vague in my original email. Sorry about that. My 
collaborator had a better example to explain:

" suppose you print a PDF onto a sheet of paper. Now print a second PDF on the 
same sheet of paper. "

That's the functionality I was trying to describe last time. Right now, we're 
stripping all the strokes off the second PDF and adding them back onto the 
first, but it's forcing us to use the mangled poppler implementation.

Here are the PDFs we are trying to superimpose.

2011-04-24-Note-14-48.pdf and 2011-04-24-Note-14-49.pdf are the source images.
out_merge.pdf is the podofoimpose result
2011-04-24-Note-14-48.xoj.pdf is what we are hoping to get. (yes, we're working 
on the xournal project =) )

We plan to call the podofo libs to integrate it into our project. It's ok if 
podofoimpose doesn't have the functionality, as long as the libs do.

Thanks for your time,
Matt

On Sun, Apr 24, 2011 at 9:18 AM, Leonard Rosenthol 
<[email protected]<mailto:[email protected]>> wrote:
Transparency is maintained at the page/graphics level. Any two pages composited 
together will maintain their transaparency.

Can you post two source PDFs and the result from podofoimpose that demonstrate 
the problem you are seeing?

Thanks,
Leonard

From: Matthew Chan [mailto:[email protected]<mailto:[email protected]>]
Sent: Saturday, April 23, 2011 8:18 PM
To: 
[email protected]<mailto:[email protected]>
Subject: [Podofo-users] transparent overlap of PDF

Hi,

I'm evaluating the Podofo libs for use in a project to replace a mangled 
poppler implementation (we used poppler to make edits and write PDFs).

One of the key things we're trying to do is replace our own implementation of a 
PDF overlay function. Our function takes two PDF documents and overlays it, 
while maintaining transparency of the PDFs.

I was wondering if there was any feature that was capable of transparently 
overlaying two PDFs in the Podofo libs? I saw the podofoimpose tool, but it 
doesn't retain PDF transparency.

Thanks in advance for your replies,
Matt

Attachment: out_merge-whites removed.pdf
Description: out_merge-whites removed.pdf

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