title: Ghostscript tiffsep creates CMYK image that is inverted in ImageMagick display?
body: <p>Not sure what to make of this - but let's say we work with this PDF file: <a href="https://stlab.adobe.com/wiki/index.php/File:Test.pdf" rel="nofollow noreferrer">https://stlab.adobe.com/wiki/index.php/File:Test.pdf</a>, and I want to obtain separations using Ghostscript's <code>tiffsep</code> device:</p>
  
  <pre class="lang-none prettyprint-override"><code>cd /tmp
  wget https://stlab.adobe.com/wiki/images/d/d3/Test.pdf
  ghostscript -q -sDEVICE=tiffsep -dNOPAUSE -dBATCH -dSAFER -r72x72 -sOutputFile=testseps.tif -dFirstPage=1 -dLastPage=1 Test.pdf
  eog testseps.tif &amp; display testseps.tif
  </code></pre>
  
  <p>This generates five files: <code>testseps(Black).tif</code>, <code>testseps(Cyan).tif</code>, <code>testseps(Magenta).tif</code>, <code>testseps.tif</code>, <code>testseps(Yellow).tif</code>. I open the full-color output (<code>testseps.tif</code>) in both Eye of Gnome (<code>eog</code>), and ImageMagick's <code>display</code>, and this is what I get (Ubuntu 14.04, MATE desktop, ghostscript 9.10, ImageMagick 6.7.7-10 2017-03-14 Q16):</p>
  
  <p><a href="https://i.stack.imgur.com/onm8M.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/onm8M.png" alt="Screenshot.png"></a> </p>
  
  <p>Namely, ImageMagick's <code>display</code> (left) shows this file with inverted colors, while Eye of Gnome (right) shows the very same file correctly?!</p>
  
  <p>So how can I get this CMYK tiff to show correctly in both <code>display</code> and Eye of Gnome? Can I somehow convert it with ImageMagick's <code>convert</code>, and what would the command line be? I've already tried something like:</p>
  
  <pre><code>convert testseps.tif -colorspace CMYK -alpha off -define quantum:polarity=min-is-white -colorspace CMYK testseps2.tif
  </code></pre>
  
  <p>... and that file again shows the same problem.</p>
  
  <p>EDIT: Also, if I try to combine the individual separations using <code>convert</code>:</p>
  
  <pre><code>convert \
  testseps\(Cyan\).tif \
  testseps\(Magenta\).tif \
  testseps\(Yellow\).tif \
  testseps\(Black\).tif \
  -set colorspace CMYK \
  -profile /usr/share/ghostscript/9.10/iccprofiles/default_cmyk.icc 
  -combine 
  combined.tif
  </code></pre>
  
  <p>... then <code>combined.tif</code> shows properly in ImageMagick <code>display</code> - but is shown as completely black in Eye of Gnome! If I add the <code>-negate</code> switch after <code>-combine</code>, then I'm back to the previous state (<code>display</code> shows inverted, <code>eog</code> shows correct)</p>
  
  <p>EDIT2: Tried to use a service <a href="http://www.rgb2cmyk.org/" rel="nofollow noreferrer">http://www.rgb2cmyk.org/</a>, to obtain a CMYK tif of the RGB screenshot posted here, and that one also shows the same bug: it is inverted in <code>display</code>, and shown correctly in Eye of Gnome.</p>
  
  <p>Just for reference, here is a bit of info about <code>testseps.tif</code>:</p>
  
  <pre><code>$ tiffinfo testseps.tif 
  TIFF Directory at offset 0x8 (8)
    Subfile Type: multi-page document (2 = 0x2)
    Image Width: 612 Image Length: 792
    Resolution: 72, 72 pixels/inch
    Bits/Sample: 8
    Compression Scheme: LZW
    Photometric Interpretation: separated
    FillOrder: msb-to-lsb
    Orientation: row 0 top, col 0 lhs
    Samples/Pixel: 4
    Rows/Strip: 428
    Planar Configuration: single image plane
    Page Number: 0-0
    Software: GPL Ghostscript 9.10
    DateTime: 2017:04:10 12:53:45
    ICC Profile: &lt;present&gt;, 56412 bytes
  $ identify -verbose testseps.tif 
  Image: testseps.tif
    Format: TIFF (Tagged Image File Format)
    Class: DirectClass
    Geometry: 612x792+0+0
    Resolution: 72x72
    Print size: 8.5x11
    Units: PixelsPerInch
    Type: ColorSeparation
    Endianess: MSB
    Colorspace: CMYK
    Depth: 8-bit
    Channel depth:
      cyan: 8-bit
      magenta: 8-bit
      yellow: 8-bit
      black: 8-bit
    Channel statistics:
      Cyan:
        min: 0 (0)
        max: 235 (0.921569)
        mean: 5.93515 (0.0232751)
        standard deviation: 33.3466 (0.130771)
        kurtosis: 28.8423
        skewness: 5.53334
      Magenta:
        min: 0 (0)
        max: 245 (0.960784)
        mean: 2.7823 (0.010911)
        standard deviation: 18.73 (0.0734511)
        kurtosis: 68.8725
        skewness: 8.12072
      Yellow:
        min: 0 (0)
        max: 255 (1)
        mean: 5.04176 (0.0197716)
        standard deviation: 30.8529 (0.120992)
        kurtosis: 34.9211
        skewness: 6.05297
      Black:
        min: 0 (0)
        max: 226 (0.886275)
        mean: 1.06569 (0.00417917)
        standard deviation: 13.7509 (0.0539252)
        kurtosis: 227.454
        skewness: 15.0002
    Image statistics:
      Overall:
        min: 0 (0)
        max: 255 (1)
        mean: 3.70622 (0.0145342)
        standard deviation: 25.5137 (0.100054)
        kurtosis: 51.8946
        skewness: 7.28691
    Total ink density: 298%
    Rendering intent: Undefined
    Gamma: 1
    Interlace: None
    Background color: cmyk(255,255,255,0)
    Border color: cmyk(223,223,223,0)
    Matte color: cmyk(189,189,189,0)
    Transparent color: cmyk(0,0,0,0)
    Compose: Over
    Page geometry: 612x792+0+0
    Dispose: Undefined
    Iterations: 0
    Compression: LZW
    Orientation: TopLeft
    Properties:
      date:create: 2017-04-10T12:53:45+02:00
      date:modify: 2017-04-10T12:53:45+02:00
      signature: 1ad1532f697fa72492fe994d79f1b67d617a34cd927f31b41e6a12214b9bc49e
      tiff:endian: lsb
      tiff:photometric: separated
      tiff:rows-per-strip: 428
      tiff:software: GPL Ghostscript 9.10
      tiff:timestamp: 2017:04:10 12:53:45
    Profiles:
      Profile-icc: 187484 bytes
        Description: Artifex CMYK SWOP Profile
        Manufacturer: Artifex CMYK SWOP Profile
        Model: Artifex CMYK SWOP Profile
        Copyright: Copyright Artifex Software 2011
    Artifacts:
      filename: testseps.tif
      verbose: true
    Tainted: True
    Filesize: 220KB
    Number pixels: 485K
    Pixels per second: 24.24MB
    User time: 0.020u
    Elapsed time: 0:01.019
    Version: ImageMagick 6.7.7-10 2017-03-14 Q16 http://www.imagemagick.org
  </code></pre>