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):

```
gswin64c.exe -sDEVICE=pdfwrite -sProcessColorModel=DeviceGray -sColorConversionStrategy=Gray -dOverrideICC -dUseCIEColor -o gray.pdf -f test.pdf

```

The result indeed only uses gray colors:

```
>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

```

(I need to use -dUseCIEColor, otherwise CMY values are >0, this is a separate problem which I havent yet solved...)

My problem: The resulting gray.pdf uses significantly different graylevels than the original test.pdf (open in your PDF viewer and compare for yourself).

Does anyone see my mistake or what I should do differently to get the same PDF but in grayscale rather than RGB colorspace?

Thank you very much!

test.pdf: <https://drive.google.com/open?id=0BzjatAIrG6P3S2F5Vng4cUhUS0U>

gray.pdf: <https://drive.google.com/open?id=0BzjatAIrG6P3cEtTY3JaaTJCS2c>