title: Ghostscript's pdfwrite to grayscale results in wrong graylevel
body: <p>I try to convert a PDF file (test.pdf, attached below) using Ghostscript (9.20 on Windows) to only use the Graylevel colorspace (not RGB or CMY):</p>
  
  <pre><code>gswin64c.exe -sDEVICE=pdfwrite -sProcessColorModel=DeviceGray -sColorConversionStrategy=Gray -dOverrideICC -dUseCIEColor -o gray.pdf -f test.pdf
  </code></pre>
  
  <p>The result indeed only uses gray colors:</p>
  
  <pre><code>&gt;gswin64c.exe -o - -sDEVICE=inkcov gray.pdf
  GPL Ghostscript 9.20 (2016-09-26)
  Copyright (C) 2016 Artifex Software, Inc.  All rights reserved.
  This software comes with NO WARRANTY: see the file PUBLIC for details.
  Processing pages 1 through 1.
  Page 1
   0.00000  0.00000  0.00000  0.92673 CMYK OK
  </code></pre>
  
  <p>(I need to use -dUseCIEColor, otherwise CMY values are >0, this is a separate problem which I havent yet solved...)</p>
  
  <p>My problem: The resulting gray.pdf uses significantly different graylevels than the original test.pdf (open in your PDF viewer and compare for yourself).</p>
  
  <p>Does anyone see my mistake or what I should do differently to get the same PDF but in grayscale rather than RGB colorspace?</p>
  
  <p>Thank you very much!</p>
  
  <p>test.pdf: <a href="https://drive.google.com/open?id=0BzjatAIrG6P3S2F5Vng4cUhUS0U" rel="nofollow noreferrer">https://drive.google.com/open?id=0BzjatAIrG6P3S2F5Vng4cUhUS0U</a></p>
  
  <p>gray.pdf: <a href="https://drive.google.com/open?id=0BzjatAIrG6P3cEtTY3JaaTJCS2c" rel="nofollow noreferrer">https://drive.google.com/open?id=0BzjatAIrG6P3cEtTY3JaaTJCS2c</a></p>