title: Convert multipage PDF to PNG with transparency
body: <p>in the moment i run into several problems by converting a PDF file to PNG.
  The transparence is lost from the source pdf file.</p>
  
  <p>I have tested the following terminal tools to create the png:
  GhostScript, Imagemagick and pdf tools from poppler-tools, always on a debian system.</p>
  
  <p>The image should have the same dimension as the pdf, also the same transparency.</p>
  
  <p>used commands:</p>
  
  <pre><code>gs -dNOPAUSE -sDEVICE=pngalpha -sOutputFile=test%d.png -r96 -q design.pdf  -c quit
  convert design.pdf test%d.png
  convert design.pdf -channel rgba -alpha on PNG32:test%d.png
  convert -background none -colorspace srgb design.pdf -colorspace srgb -channel rgba -alpha on PNG32:test%d.png
  pdftoppm -png file.pdf test
  </code></pre>
  
  <p>The result is not the expected png with transparency. The Background is white, should be 100% transparent. Additionaly there is a green bar and should be semi-transparent. In all my tries the result ends up in a lighter green box with no transparency.</p>
  
  <p>To see my result, i have uploaded the source pdf, faulty created png and the expected result (export from photoshop).</p>
  
  <pre><code>PDF: http://speedy.sh/W75HP/source-file.pdf
  Result: http://speedy.sh/hfZMt/faulty-created-design.png
  Expected: http://speedy.sh/7mpEk/design-the-way-it-should-be.png
  </code></pre>
  
  <p>I managed to get the white background to be transparent, but the actual file transparency including the semi-transparent green bar/box is not converted properly.</p>
  
  <p>Whats the solution for my issue?</p>
  
  <p>Best regards,
  Chris</p>
  
  <p>//UPDATE
  Okay we have found a solution with another 3th party tool which produces my expected result on a easy way.</p>
  
  <pre><code>inkscape design.pdf -z --export-dpi=100 --export-png=design.png
  </code></pre>
  
  <p>Thx for help</p>