title: Camelot ignoring backend request
body: <p>I recently got into camelot and but for some reason need to use my own backend to remove text during the imaging process.</p>
  <p>Here is what I tried based on the documentation:</p>
  <pre><code>class ConversionBackend(object):
      def convert(pdf_path, png_path):
          arg2 = '-sOutputFile=' + png_path
          p = subprocess.Popen(['/usr/bin/gs', '-sDEVICE=png16m', '-dNOPAUSE', '-dBATCH', '-dQUIET', &quot;-dFILTERIMAGE&quot;, &quot;-dFILTERTEXT&quot;, &quot;-r300&quot;,str(arg2), pdf_path], stdout = subprocess.PIPE)
          pass`
  </code></pre>
  <p>Aside from the fact that my ghostscript use is not optimal, all of this runs does work when I run it step by step in the python console. However when calling camelot using</p>
  <pre><code>tables = camelot.read_pdf(path, line_scale=100, split_text=True, flag_size=True, layout_kwargs={'detect_vertical': False, 'char_margin': 2.0}, pages='all', backend=ConversionBackend())
  </code></pre>
  <p>Camelot still executes my command but with complete disregard for the <code>backend=ConversionBackend()</code></p>
  <p>Any ideas on how to fix this?</p>
  <p>Sh4yce</p>