[Image-SIG] pdf to image

[Carl Karsten]

For the PyCon registration web page, we would like to display a preview of what 
the persons badge will look like based on what they have entered.  (full name, 
nick name, extra lines in the fonts that will be used - helps make sure things 
will fit, etc.)

The badge gets created as a pdf=mkpdf(data set) - we can just give the person 
the pdf, but we are trying to put it on the web page with <img src..> so we need 
  to convert the pdf to an image.  I can't find a clean way of doing it.  I 
found no ghostscript bindings, and the 2 imagemagick bindings either screwed up 
stdio or segfaulted.  The best I could do is below, and it is causing this to 
show up in the error log:
close failed: [Errno 10] No child processes

and stack dumps:

 >     subprocess.call(gs_command)
 >
 >   File "/usr/local/lib/python2.5/subprocess.py", line 443, in call
 >     return Popen(*popenargs, **kwargs).wait()
 >
 >   File "/usr/local/lib/python2.5/subprocess.py", line 1110, in wait
 >     pid, sts = os.waitpid(self.pid, 0)
 >
 > OSError: [Errno 10] No child processes

here is the current code:

def sample(pdf):

     tempDir = tempfile.mkdtemp( prefix = "badgePreview_" )
     pdfname = path.join( tempDir, 'badge.pdf' )
     imgname = path.join( tempDir, 'badge.png' )

     open(pdfname,'wb').write(pdf)

     # convert pdf to some image format (uses ext to determine type)
     # system('convert %s %s' % (pdfname, imgname))
     # gs -sDEVICE=png16m -sOutputFile=x.png -dBATCH -dNOPAUSE badge.pdf
     gs_command = ['gs',
         '-q',
         '-sDEVICE=png16m',
         '-dBATCH', '-dNOPAUSE',
         '-sOutputFile=%s'%imgname,
         pdfname ]
     subprocess.call(gs_command)

     # crop the badge (pdf may be 8x11 page)
     # and write to a string that can be reutnred
     buffer = StringIO()
     Image.open(imgname).crop([0,0,300,235]).save(buffer, 'png')
     img = buffer.getvalue()

     # clean up
     buffer.close()
     remove(pdfname)
     remove(imgname)
     rmdir(tempDir)

     return img

So.... anyone have some nifty code?

Carl K