Ghostscript and Pantone/spotcolors - linux

Question

I have some pdf's for professional print that are put in a certain folder. These pdf's may or may not contain spot/Pantone colors. All files in this folder get processed.
I have to cut some white space from the edges and this works fine with Ghostscript 8.7 on a linux machine using the command:
gs \
-o correct_size.pdf \
-sDEVICE=pdfwrite \
-g1000x1000 \
-dPDFSETTINGS=/prepress \
-c "<</PageOffset [0 0]>> setpagedevice" \
-f original_size.pdf
This problem is the spot/Pantone colors aren't preserved.
The documentation speaks about handling spotcolors but doesn't really give a solution.
Has anyone come across this before or does anyone have another solution? It doesn't have to involve Ghostscript.

Answer 1

Using a version of Ghostscript less than 5 years old would be a good place to start!
The current version of pdfwrite will retain colour spaces, including Separation (what you are calling spot) ICCBased and DeviceN. It is also capable of retaining Separation colour spaces when converting to a different device space, by resampling the tint transform into the desired space.
Secondly, don't use the canned PDFSETTINGS unless you are very sure you understand what the settings mean. In general the default settings in pdfwrite will preserve unchanged anything in the original file that it can, the PDFSETTINGS are set to follow (as far as possible) the same settings in Adobe Acrobat Distiller. If you aren't certain what these do, the documentation details it.

Answer 2

If you want to know exactly, what the canned -dPDFSETTINGS=/prepress do, you can query your current version of Ghostscript with this command:
gs -q \
-dPDFSETTINGS=/prepress \
-o /dev/null \
-sDEVICE=pdfwrite \
-c "currentpagedevice {exch ==only ( ) print == } forall" \
| sort
In my case, I get this for a Ghostscript 9.16 (self-compiled from Ghostscript's current Git source respository):
/%MediaDestination 0
/%MediaSource 0
/.AlwaysEmbed []
/.HWMargins [0.0 0.0 0.0 0.0]
/.IgnoreNumCopies false
/.LockSafetyParams false
/.MarginsHWResolution [720.0 720.0]
/.MediaSize [612.0 792.0]
/.NeverEmbed []
/ASCII85EncodePages false
/AllowIncrementalCFF false
/AllowPSRepeatFunctions false
/AlwaysEmbed []
/AntiAliasColorImages false
/AntiAliasGrayImages false
/AntiAliasMonoImages false
/AutoFilterColorImages true
/AutoFilterGrayImages true
/AutoPositionEPSFiles true
/AutoRotatePages /None
/BandBufferSpace 0
/BandHeight 0
/BandWidth 0
/BeginPage {--.callbeginpage--}
/Binding /Left
/BitsPerPixel 24
/BlackPtComp 8
/BlueValues 256
/BufferSpace 4000000
/CalCMYKProfile (None)
/CalGrayProfile (None)
/CalRGBProfile (None)
/CannotEmbedFontPolicy /Error
/CenterPages false
/ColorACSImageDict -dict-
/ColorAutoFilterStrategy 248456437
/ColorConversionStrategy /LeaveColorUnchanged
/ColorImageDepth -1
/ColorImageDict -dict-
/ColorImageDownsampleThreshold 1.5
/ColorImageDownsampleType /Bicubic
/ColorImageFilter /DCTEncode
/ColorImageResolution 300
/ColorValues 16777216
/Colors 3
/CompatibilityLevel 1.5
/CompressEntireFile false
/CompressFonts true
/CompressPages true
/ConvertCMYKImagesToRGB false
/ConvertImagesToIndexed true
/CoreDistVersion 5000
/CreateJobTicket true
/DSCEncodingToUnicode []
/DefaultRenderingIntent /Default
/DetectBlends true
/DetectDuplicateImages true
/DeviceGrayToK true
/DeviceLinkProfile ()
/DoNumCopies false
/DoThumbnails true
/DocumentTimeSeq 0
/DocumentUUID ()
/DownsampleColorImages true
/DownsampleGrayImages true
/DownsampleMonoImages true
/EmbedAllFonts true
/EmitDSCWarnings false
/EncodeColorImages true
/EncodeGrayImages true
/EncodeMonoImages true
/EncryptionR 0
/EndPage {--.callendpage--}
/FastWebView false
/FirstObjectNumber 1
/FirstPage 0
/FitPages false
/ForOPDFRead false
/GraphicBlackPt 8
/GraphicICCProfile ()
/GraphicIntent 8
/GraphicKPreserve 8
/GraphicsAlphaBits 1
/GrayACSImageDict -dict-
/GrayAutoFilterStrategy 248456437
/GrayDetection false
/GrayImageDepth -1
/GrayImageDict -dict-
/GrayImageDownsampleThreshold 1.5
/GrayImageDownsampleType /Bicubic
/GrayImageFilter /DCTEncode
/GrayImageResolution 300
/GrayValues 256
/GreenValues 256
/HWResolution [720.0 720.0]
/HWSize [6120 7920]
/HaveCIDSystem false
/HaveTransparency true
/HaveTrueTypes true
/HighLevelDevice true
/ICCOutputColors ()
/ImageBlackPt 8
/ImageICCProfile ()
/ImageIntent 8
/ImageKPreserve 8
/ImageMemory 524288
/ImagingBBox null
/InputAttributes -dict-
/Install {--.callinstall--}
/InstanceUUID ()
/IsDistiller true
/KPreserve 8
/KeyLength 0
/LZWEncodePages false
/LastPage 0
/Margins [0.0 0.0]
/MaxBitmap 10000000
/MaxClipPathSize 12000
/MaxInlineImageSize 4000
/MaxPatternBitmap 0
/MaxSeparations 3
/MaxShadingBitmapSize 256000
/MaxSubsetPct 100
/MonoImageDepth -1
/MonoImageDict -dict-
/MonoImageDownsampleThreshold 1.5
/MonoImageDownsampleType /Bicubic
/MonoImageFilter /CCITTFaxEncode
/MonoImageResolution 1200
/Name (pdfwrite)
/NeverEmbed []
/NoEncrypt ()
/NoOutputFonts false
/NoT3CCITT false
/NumCopies null
/OPM 1
/OffOptimizations 0
/Optimize true
/OutputAttributes -dict-
/OutputDevice /pdfwrite
/OutputFile (/dev/null)
/OutputICCProfile (default_rgb.icc)
/OwnerPassword ()
/PDFA 0
/PDFACompatibilityPolicy 0
/PDFEndPage -1
/PDFStartPage 1
/PDFUseOldCMS false
/PDFX false
/PDFXBleedBoxToTrimBoxOffset [0.0 0.0 0.0 0.0]
/PDFXSetBleedBoxToMediaBox true
/PDFXTrimBoxToMediaBoxOffset [0.0 0.0 0.0 0.0]
/PageCount 0
/PageDeviceName null
/PageOffset [0 0]
/PageSize [612.0 792.0]
/PageUsesTransparency false
/ParseDSCComments true
/ParseDSCCommentsForDocInfo true
/PatternImagemask false
/Permissions -4
/Policies -dict-
/PreBandThreshold false
/PreserveCopyPage true
/PreserveDeviceN true
/PreserveEPSInfo true
/PreserveHalftoneInfo false
/PreserveOPIComments true
/PreserveOverprintSettings true
/PreserveSMask true
/PreserveSeparation true
/PreserveTrMode true
/PrintStatistics false
/ProcessColorModel /DeviceRGB
/ProduceDSC true
/ProofProfile ()
/ReAssignCharacters true
/ReEncodeCharacters true
/RedValues 256
/RenderIntent 8
/RotatePages false
/SeparationColorNames []
/Separations false
/SetPageSize true
/SimulateOverprint true
/SubsetFonts true
/TextAlphaBits 1
/TextBlackPt 8
/TextICCProfile ()
/TextIntent 8
/TextKPreserve 8
/TransferFunctionInfo /Preserve
/UCRandBGInfo /Preserve
/UseCIEColor false
/UseFastColor false
/UseFlateCompression true
/UsePrologue false
/UserPassword ()
/WantsToUnicode true
/sRGBProfile (None)
If you want to use -dPDFSETTINGS=/prepress, but with some tweaks of your own, you can look up the known parameters and their canned values with above command.
Then add a suitable -c ".setpdfwrite << ... >> setdistillerparams" modification to your Ghostscript command (example is arbitrary):
gs \
-dPDFSETTINGS=/prepress \
-o out.pdf \
-sDEVICE=pdfwrite \
[...more commandline switches...] \
-c ".setpdfwrite<</Optimize false/NeverEmbed[/Courier/Verdana]>>setdistillerparams" \
-f input.pdf