Querying Ghostscript for the default options/settings of an output device (such as 'pdfwrite' or 'tiffg4')

Question

In this answer to 'GhostScript command line parameters to convert EPS to PDF'; it is stated that the default resolution for the pdfwrite device of Ghostscript is 720x720, which I initially found unbelievable!

Is there a way to list the default options of a Ghostscript device?

Answer 1

Since Ghostscript is a full-blown PostScript interpreter, you can also send PostScript snippets to it which do not cause the drawing of page elements, but which query it for its internal state.

If you want to know what the default settings of the Display are, when you ask it via gs some.pdf to just display a PDF on screen, you could try this:

gs \
   -c "currentpagedevice {exch ==only ( ) print == } forall"

On Windows this becomes:

gswin32c.exe ^
   -c "currentpagedevice {exch ==only ( ) print == } forall"

The result is a list of /SomeName somevalue pairs which describe the settings used for rendering pages to the current screen.

This is so because usually the display is the default device for Ghostscript to send its output to. Now you may notice that you'll see an empty Ghostscript window pop up, which you'll have to close.... Ah, how about adding some options to avoid the popup window?

gs \
   -o /dev/null \
   -dNODISPLAY \
   -c "currentpagedevice {exch ==only ( ) print == } forall"

Or, on Windows:

gswin32c.exe ^
   -o nul ^
   -dNODISPLAY ^
   -c "currentpagedevice {exch ==only ( ) print == } forall"

But this will change the query return values, because you (unintentionally) changed the output device settings:

gs -c "currentpagedevice {exch ==only ( ) print == } forall" | grep Resolution

Result:

HWResolution [86.5426483 86.5426483]
/.MarginsHWResolution [1152.0 1152.0]

Compare this to

gs \
   -o /dev/null \
   -dNODISPLAY \
   -c "currentpagedevice {exch ==only ( ) print == } forall" \
| grep Resolution

Result:

/HWResolution [72.0 72.0]
/.MarginsHWResolution [72.0 72.0]

So, please avoid this trap. I successfully fell into it a few years ago, and didn't even notice it for quite a long time...

Now assuming you want to query for the default settings of the PDF writing device, run this one:

gs \
  -o /dev/null \
  -sDEVICE=pdfwrite \
  -c "currentpagedevice {exch ==only ( ) print == } forall" \
| tee ghostscript-pdfwrite-default-pagedevice-settings.txt

You'll now have all settings for the pdfwrite device in a *.txt file. and you may repeat that with some other interesting Ghostscript devices and then compare them for all their detailled differences:

for _dev in \
  pswrite ps2write pdfwrite \
  tiffg3 tiffg4 tiff12nc tiff24nc tiff32nc tiff48nc tiffsep \
  jpeg jpeggray jpegcmyk \
  png16 png16m png256 png48 pngalpha pnggray pngmono; \
do \
  gs \
    -o /dev/null \
    -sDEVICE=${_dev} \
    -c "currentpagedevice {exch ==only ( ) print == } forall" \
   | sort \
   | tee ghostscript-${_dev}-default-pagedevice-settings.txt; \
done

It's rather interesting to compare the settings for, say, the pswrite and ps2write devices like this (and also discover parameters which are available for the one, but not the other device):

sdiff -sbB ghostscript-ps*write-default-pagedevice-settings.txt

---

Update:

As you may imagine this is also a great way to compare different Ghostscript versions, and track how default settings may have changed for different devices in recent releases. This is especially interesting if you want to find out about all the newly implemented color profile and ICC support which is now present in Ghostscript.

Also, to avoid the return of just -dict- for certain key values, use the === instead of == macro. === acts like == but also prints the content of dictionaries.

So here is the example output for the pdfwrite device. Remember, Ghostscript's pdfwrite device is meant to provide mostly the same functionality as Adobe Acrobat Distiller (with the additional feature that it does not only accept PostScript as input, but also PDFs, so you can sort of redistill existing PDF files in order to repair, improve or otherwise manipulate them). Therefore, Ghostscript's pdfdevice honors most of the setdistillerparams operator which the original Distiller also supports:

gs \
  -o /dev/null \
  -sDEVICE=pdfwrite \
  -c "currentpagedevice {exch ==only ( ) print === } forall" \
| sort

/%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 [/Courier /Courier-Bold /Courier-Oblique /Courier-BoldOblique /Helvetica /Helvetica-Bold /Helvetica-Oblique /Helvetica-BoldOblique /Times-Roman /Times-Bold /Times-Italic /Times-BoldItalic /Symbol /ZapfDingbats]
/ASCII85EncodePages false
/AllowIncrementalCFF false
/AllowPSRepeatFunctions false
/AlwaysEmbed []
/AntiAliasColorImages false          [*]
/AntiAliasGrayImages false           [*]
/AntiAliasMonoImages false           [*]
/AutoFilterColorImages true
/AutoFilterGrayImages true
/AutoPositionEPSFiles true
/AutoRotatePages /PageByPage
/BeginPage {--.callbeginpage--}
/Binding /Left                       [*]
/BitsPerPixel 24
/BlueValues 256
/CalCMYKProfile (None)               [*]
/CalGrayProfile (None)               [*]
/CalRGBProfile (None)                [*]
/CannotEmbedFontPolicy /Warning      [*]
/CenterPages false
/ColorACSImageDict << /Blend 1 /VSamples [2 1 1 2] /QFactor 0.9 /HSamples [2 1 1 2] >>
/ColorConversionStrategy /LeaveColorUnchanged
/ColorImageDepth -1
/ColorImageDict << /Blend 1 /VSamples [2 1 1 2] /QFactor 0.9 /HSamples [2 1 1 2] >>
/ColorImageDownsampleThreshold 1.5
/ColorImageDownsampleType /Subsample
/ColorImageFilter /DCTEncode
/ColorImageResolution 150
/ColorValues 16777216
/Colors 3
/CompatibilityLevel 1.4
/CompressEntireFile false
/CompressFonts true
/CompressPages true
/ConvertCMYKImagesToRGB false
/ConvertImagesToIndexed true
/CoreDistVersion 5000
/CreateJobTicket false               [*]
/DSCEncodingToUnicode []
/DefaultRenderingIntent /Default
/DetectBlends true                   [*]
/DetectDuplicateImages true
/DeviceGrayToK true
/DeviceLinkProfile ()
/DoNumCopies false
/DoThumbnails false                  [*]
/DocumentTimeSeq 0
/DocumentUUID ()
/DownsampleColorImages false
/DownsampleGrayImages false
/DownsampleMonoImages false
/EmbedAllFonts true
/EmitDSCWarnings false               [*]
/EncodeColorImages true
/EncodeGrayImages true
/EncodeMonoImages true
/EncryptionR 0
/EndPage {--.callendpage--}          [*]
/FirstObjectNumber 1
/FitPages false
/ForOPDFRead false
/GraphicICCProfile ()
/GraphicIntent 0
/GraphicsAlphaBits 1
/GrayACSImageDict << /Blend 1 /VSamples [2 1 1 2] /QFactor 0.9 /HSamples [2 1 1 2] >>
/GrayImageDepth -1
/GrayImageDict << /Blend 1 /VSamples [2 1 1 2] /QFactor 0.9 /HSamples [2 1 1 2] >>
/GrayImageDownsampleThreshold 1.5
/GrayImageDownsampleType /Subsample
/GrayImageFilter /DCTEncode
/GrayImageResolution 150
/GrayValues 256
/GreenValues 256
/HWResolution [720.0 720.0]
/HWSize [6120 7920]
/HaveCIDSystem false
/HaveTransparency true
/HaveTrueTypes true
/HighLevelDevice true
/ImageICCProfile ()
/ImageIntent 0
/ImageMemory 524288                  [*]
/ImagingBBox null
/InputAttributes << 59 << /PageSize [612 792] >> 36 << /PageSize [649 918] >> 13 << /PageSize [595 842] >> 49 << /PageSize [354 499] >> 26 << /PageSize [2004 2835] >> 3 << /PageSize [792 1224] >> 62 << /PageSize [595 792] >> 39 << /PageSize [612 936] >> 16 << /PageSize [297 420] >> 52 << /PageSize [1460 2064] >> 29 << /PageSize [709 1001] >> 6 << /PageSize [2448 3168] >> 42 << /PageSize [396 612] >> 19 << /PageSize [105 148] >> 55 << /PageSize [516 729] >> 32 << /PageSize [2599 3677] >> 9 << /PageSize [1684 2384] >> 45 << /PageSize [1417 2004] >> 22 << /PageSize [1296 1728] >> 58 << /PageSize [612 1008] >> 35 << /PageSize [918 1298] >> 12 << /PageSize [842 1191] >> 48 << /PageSize [499 709] >> 25 << /PageSize [2835 4008] >> 2 << /PageSize [612 792] >> 61 << /PageSize [612 792] >> 38 << /PageSize [323 459] >> 15 << /PageSize [420 595] >> 51 << /PageSize [2064 2920] >> 28 << /PageSize [1001 1417] >> 5 << /PageSize [1585 2448] >> 64 << /PageSize [0 0 524287 524287] >> 41 << /PageSize [283 420] >> 18 << /PageSize [148 210] >> 54 << /PageSize [729 1032] >> 31 << /PageSize [354 499] >> 8 << /PageSize [2384 3370] >> 44 << /PageSize [2004 2835] >> 21 << /PageSize [864 1296] >> 57 << /PageSize [1224 792] >> 34 << /PageSize [1298 1837] >> 11 << /PageSize [1191 1684] >> 47 << /PageSize [709 1001] >> 24 << /PageSize [2592 3456] >> 1 << /PageSize [792 1224] >> 60 << /PageSize [612 792] >> 37 << /PageSize [459 649] >> 14 << /PageSize [595 842] >> 50 << /PageSize [2920 4127] >> 27 << /PageSize [1417 2004] >> 4 << /PageSize [1224 1585] >> 63 << /PageSize [792 1224] >> 40 << /PageSize [612 936] >> 17 << /PageSize [210 297] >> 53 << /PageSize [1032 1460] >> 30 << /PageSize [499 709] >> 7 << /PageSize [2016 2880] >> 43 << /PageSize [2835 4008] >> 20 << /PageSize [648 864] >> 56 << /PageSize [363 516] >> 33 << /PageSize [1837 2599] >> 10 << /PageSize [73 105] >> 46 << /PageSize [1001 1417] >> 23 << /PageSize [1728 2592] >> 0 << /PageSize [612.0 792.0] >> >>
/Install {--.callinstall--}
/InstanceUUID ()
/IsDistiller true
/KeyLength 0
/LZWEncodePages false
/Margins [0.0 0.0]
/MaxClipPathSize 12000
/MaxInlineImageSize 4000
/MaxPatternBitmap 0
/MaxSeparations 3
/MaxShadingBitmapSize 256000
/MaxSubsetPct 100
/MaxViewerMemorySize -1
/MonoImageDepth -1
/MonoImageDict << /K -1 >>
/MonoImageDownsampleThreshold 1.5
/MonoImageDownsampleType /Subsample
/MonoImageFilter /CCITTFaxEncode
/MonoImageResolution 300
/Name (pdfwrite)
/NeverEmbed [/Courier /Courier-Bold /Courier-Oblique /Courier-BoldOblique /Helvetica /Helvetica-Bold /Helvetica-Oblique /Helvetica-BoldOblique /Times-Roman /Times-Bold /Times-Italic /Times-BoldItalic /Symbol /ZapfDingbats]
/NoEncrypt ()
/NoT3CCITT false
/NumCopies null
/OPM 1
/OffOptimizations 0
/Optimize false                      [*]
/OutputAttributes << 0 << >> >>
/OutputDevice /pdfwrite
/OutputFile (/dev/null)
/OutputICCProfile (default_rgb.icc)
/OwnerPassword ()
/PDFA 0
/PDFACompatibilityPolicy 0
/PDFEndPage -1
/PDFStartPage 1
/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]
/ParseDSCComments true
/ParseDSCCommentsForDocInfo true
/PatternImagemask false
/Permissions -4
/Policies << /PolicyReport {--dup-- /.LockSafetyParams --known-- {/setpagedevice --.systemvar-- /invalidaccess signalerror} --if-- --pop--} /PageSize 0 /PolicyNotFound 1 >>
/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 0
/RotatePages false
/SeparationColorNames []
/Separations false
/SetPageSize false
/SubsetFonts true
/TextAlphaBits 1
/TextICCProfile ()
/TextIntent 0
/TransferFunctionInfo /Preserve
/UCRandBGInfo /Preserve
/UseCIEColor false
/UseFastColor false
/UseFlateCompression true
/UsePrologue false                   [*]
/UserPassword ()
/WantsToUnicode true
/sRGBProfile (None)                  [*]

[*] Note:

According to the official documentation, the following settings (which are supported by Adobe Acrobat Distiller) currently on Ghostscript can be set and queried, but setting them does have no effect:

• /AntiAliasColorImages
• /AntiAliasGrayImages
• /AntiAliasMonoImages
• /AutoPositionEPSFiles
• /Binding
• /CalCMYKProfile
• /CalGrayProfile
• /CalRGBKProfile
• /CannotEmbedFontPolicy
• /ConvertImagesToIndexed
• /CreateJobTicket
• /DetectBlends
• /DoThumbnails
• /EmitDSCWarnings
• /EndPage
• /ImageMemory
• /LockDistillerParams
• /Optimize
• /PreserveCopyPage
• /PreserveEPSInfo
• /PreserveHalftoneInfo
• /PreserveOPIComments
• /sRGBProfile
• /StartPage
• /UsePrologue