下のような pdf ファイルのファイルサイズを減らすことを考える。
$ pdfinfo *******.pdf Creator: pdftk 2.01 - www.pdftk.com Producer: itext-paulo-155 (itextpdf.sf.net-lowagie.com) CreationDate: Fri Mar 14 16:44:32 2014 ModDate: Fri Mar 14 16:44:32 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 149551168 bytes Optimized: no PDF version: 1.7
処理後ファイルサイズの比較。gs で画像の解像度を変えるオプションをつけた場合 (/screen, /ebook, /printer, /prepress) は画像サイズとディスプレイの解像度によってはかなり粗が目立つ。これに対して gs の/default オプションはサイズも少ないし、画像の粗も無い。元の pdf ファイルに含まれる画像の解像度がそもそも高い場合は解像度を帰るオプションを使うと処理が増えるし粗も目立つと良いこと無し。その他のコマンドを使った場合は gs に比べて圧縮されにくい。
| 処理 | user + sys | ファイルサイズ | 元ファイルに対する割合 |
| 元ファイル | - | 149551168 bytes | 100 % |
| gs -dPDFSETTINGS=/default | 335.66100 seconds | 10673382 bytes | 7.13694325677215707200 % |
| gs -dPDFSETTINGS=/screen | 559.16700 seconds | 24716043 bytes | 16.52681375246765040300 % |
| gs -dPDFSETTINGS=/ebook | 545.50600 seconds | 25966350 bytes | 17.36285336133249056200 % |
| gs -dPDFSETTINGS=/printer | 351.71800 seconds | 12383032 bytes | 8.28013058380125790700 % |
| gs -dPDFSETTINGS=/prepress | 354.47800 seconds | 14157700 bytes | 9.46679333189828380300 % |
| pdfopt | 24.11800 seconds | 149536440 bytes | 99.99015186561431603100 % |
| pdftk compress | 18.85400 seconds | 147370039 bytes | 98.54155000648339971500 % |
| qpdf --linearize | 39.89800 seconds | 148749860 bytes | 99.46419141306873644700 % |
具体的なコマンド例。
$ time gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/default -dNOPAUSE -dQUIET -dBATCH -sOutputFile=*******-default.pdf *******.pdf warning: ignoring invalid option raw **** Warning: File has insufficient data for an image. warning: ignoring invalid option raw warning: ignoring invalid option raw warning: ignoring invalid option raw **** This file had errors that were repaired or ignored. **** The file was produced by: **** >>>> itext-paulo-155 (itextpdf.sf.net-lowagie.com) <<<< **** Please notify the author of the software that produced this **** file that it does not conform to Adobe's published PDF **** specification. real 12m1.275s user 5m20.432s sys 0m15.229s $ pdfinfo *******-default.pdf Producer: GPL Ghostscript 9.05 CreationDate: Sat Mar 15 02:07:56 2014 ModDate: Sat Mar 15 02:07:56 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 10673382 bytes Optimized: no PDF version: 1.4 $ time gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=*******-screen.pdf *******.pdf warning: ignoring invalid option raw **** Warning: File has insufficient data for an image. warning: ignoring invalid option raw warning: ignoring invalid option raw warning: ignoring invalid option raw **** This file had errors that were repaired or ignored. **** The file was produced by: **** >>>> itext-paulo-155 (itextpdf.sf.net-lowagie.com) <<<< **** Please notify the author of the software that produced this **** file that it does not conform to Adobe's published PDF **** specification. real 18m31.787s user 8m52.941s sys 0m26.226s $ pdfinfo *******-screen.pdf Producer: GPL Ghostscript 9.05 CreationDate: Sat Mar 15 02:44:24 2014 ModDate: Sat Mar 15 02:44:24 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 24716043 bytes Optimized: no PDF version: 1.4 $ time gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=*******-ebook.pdf *******.pdf warning: ignoring invalid option raw **** Warning: File has insufficient data for an image. warning: ignoring invalid option raw warning: ignoring invalid option raw warning: ignoring invalid option raw **** This file had errors that were repaired or ignored. **** The file was produced by: **** >>>> itext-paulo-155 (itextpdf.sf.net-lowagie.com) <<<< **** Please notify the author of the software that produced this **** file that it does not conform to Adobe's published PDF **** specification. real 18m1.188s user 8m31.068s sys 0m34.438s $ pdfinfo *******-ebook.pdf Producer: GPL Ghostscript 9.05 CreationDate: Sat Mar 15 03:02:57 2014 ModDate: Sat Mar 15 03:02:57 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 25966350 bytes Optimized: no PDF version: 1.4 $ time gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/printer -dNOPAUSE -dQUIET -dBATCH -sOutputFile=*******-printer.pdf *******.pdf GPL Ghostscript 9.05: Set UseCIEColor for UseDeviceIndependentColor to work properly. warning: ignoring invalid option raw **** Warning: File has insufficient data for an image. warning: ignoring invalid option raw warning: ignoring invalid option raw warning: ignoring invalid option raw **** This file had errors that were repaired or ignored. **** The file was produced by: **** >>>> itext-paulo-155 (itextpdf.sf.net-lowagie.com) <<<< **** Please notify the author of the software that produced this **** file that it does not conform to Adobe's published PDF **** specification. real 11m30.515s user 5m22.464s sys 0m29.254s $ pdfinfo *******-printer.pdf Producer: GPL Ghostscript 9.05 CreationDate: Sat Mar 15 03:21:05 2014 ModDate: Sat Mar 15 03:21:05 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 12383032 bytes Optimized: no PDF version: 1.4 $ time gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/prepress -dNOPAUSE -dQUIET -dBATCH -sOutputFile=*******-prepress.pdf *******.pdf warning: ignoring invalid option raw **** Warning: File has insufficient data for an image. warning: ignoring invalid option raw warning: ignoring invalid option raw warning: ignoring invalid option raw **** This file had errors that were repaired or ignored. **** The file was produced by: **** >>>> itext-paulo-155 (itextpdf.sf.net-lowagie.com) <<<< **** Please notify the author of the software that produced this **** file that it does not conform to Adobe's published PDF **** specification. real 10m4.432s user 5m24.456s sys 0m30.022s $ pdfinfo *******-prepress.pdf Producer: GPL Ghostscript 9.05 CreationDate: Sat Mar 15 03:32:31 2014 ModDate: Sat Mar 15 03:32:31 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 14157700 bytes Optimized: no PDF version: 1.4
ghostscript の PDFSETTINGS オプションで与えることのできるスイッチ (/prepress, /ebook, /screen, /printer, /default) の内容を具体的にあらわすと以下。基本的にはファイルサイズの大きくなる順に /screen < /ebook < /printer < /prepress。それぞれのオプションを使うことでどのように設定されるかを確認するには以下のようにする。
$ gs -q -dPDFSETTINGS=/prepress -o /dev/null -sDEVICE=pdfwrite -c "currentpagedevice {exch ==only ( ) print == } forall" | sort | less
例えば、以下のようにすれば、/prepress と /screen で変化するオプションの種類を確認できる。
$ diff <(gs -q -dPDFSETTINGS=/prepress -o /dev/null -sDEVICE=pdfwrite -c "currentpagedevice {exch ==only ( ) print == } forall" | sort) <(gs -q -dPDFSETTINGS=/screen -o /dev/null -sDEVICE=pdfwrite -c "currentpagedevice {exch ==only ( ) print == } forall" | sort)
9c9
< /.NeverEmbed []
---
> /.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]
20c20
< /AutoRotatePages /None
---
> /AutoRotatePages /PageByPage
33c33
< /CannotEmbedFontPolicy /Error
---
> /CannotEmbedFontPolicy /Warning
36c36
< /ColorConversionStrategy /LeaveColorUnchanged
---
> /ColorConversionStrategy /sRGB
41c41
< /ColorImageDownsampleType /Bicubic
---
> /ColorImageDownsampleType /Average
43c43
< /ColorImageResolution 300
---
> /ColorImageResolution 72
53c53
< /CreateJobTicket true
---
> /CreateJobTicket false
61c61
< /DoThumbnails true
---
> /DoThumbnails false
90c90
< /GrayImageDownsampleType /Bicubic
---
> /GrayImageDownsampleType /Average
92c92
< /GrayImageResolution 300
---
> /GrayImageResolution 72
127c127
< /MonoImageDownsampleType /Bicubic
---
> /MonoImageDownsampleType /Average
129c129
< /MonoImageResolution 1200
---
> /MonoImageResolution 300
131c131
< /NeverEmbed []
---
> /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]
163c163
< /PreBandThreshold false
---
> /PreBandThreshold true
166c166
< /PreserveEPSInfo true
---
> /PreserveEPSInfo false
168,169c168,169
< /PreserveOPIComments true
< /PreserveOverprintSettings true
---
> /PreserveOPIComments false
> /PreserveOverprintSettings false
193c193
< /UCRandBGInfo /Preserve
---
> /UCRandBGInfo /Remove
$ gs -dNODISPLAY -c ".distillersettings {exch ==only ( ) print ===} forall quit" | less
GPL Ghostscript 9.05 (2012-02-08)
Copyright (C) 2010 Artifex Software, Inc. All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
/prepress << /MonoImageResolution 1200 /ColorImageDownsampleType /Bicubic /PreserveEPSInfo true /ColorConversionStrategy /LeaveColorUnchanged /GrayImageDownsampleType /Bicubic /EmbedAllFonts true /CannotEmbedFontPolicy /Error /PreserveOPIComments true /GrayImageResolution 300 /GrayACSImageDict << /ColorTransform 1 /QFactor 0.15 /Blend 1 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageResolution 300 /PreserveOverprintSettings true /CreateJobTicket true /AutoRotatePages /None /MonoImageDownsampleType /Bicubic /NeverEmbed [] /ColorACSImageDict << /ColorTransform 1 /QFactor 0.15 /Blend 1 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /CompatibilityLevel 1.4 /UCRandBGInfo /Preserve /DoThumbnails true >>
/PSL2Printer << /CompatibilityLevel 1.2 /TransferFunctionInfo /Preserve /MonoImageResolution 1200 /PreserveEPSInfo true /CompressFonts true /ColorImageDownsampleType /Bicubic /GrayImageDownsampleType /Bicubic /ColorConversionStrategy /LeaveColorUnchanged /EmbedAllFonts true /ColorACSImageDict << /ColorTransform 1 /QFactor 0.15 /Blend 1 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /CannotEmbedFontPolicy /Error /PreserveOPIComments true /CompressPages true /GrayImageResolution 600 /GrayACSImageDict << /ColorTransform 1 /QFactor 0.15 /Blend 1 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageResolution 600 /PreserveOverprintSettings true /AutoRotatePages /None /MonoImageDownsampleType /Bicubic /ASCII85EncodePages true /MaxViewerMemorySize 8000000 /NeverEmbed [] /PreserveHalftoneInfo true /UCRandBGInfo /Preserve /DoThumbnails false >>
/ebook << /MonoImageResolution 300 /ColorImageDownsampleType /Bicubic /PreserveEPSInfo false /ColorConversionStrategy /sRGB /GrayImageDownsampleType /Bicubic /EmbedAllFonts true /CannotEmbedFontPolicy /Warning /PreserveOPIComments false /GrayImageResolution 150 /GrayACSImageDict << /ColorTransform 1 /QFactor 0.76 /Blend 1 /HSamples [2 1 1 2] /VSamples [2 1 1 2] >> /ColorImageResolution 150 /PreserveOverprintSettings false /CreateJobTicket false /AutoRotatePages /All /MonoImageDownsampleType /Bicubic /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] /ColorACSImageDict << /ColorTransform 1 /QFactor 0.76 /Blend 1 /HSamples [2 1 1 2] /VSamples [2 1 1 2] >> /CompatibilityLevel 1.4 /UCRandBGInfo /Remove /DoThumbnails false >>
/screen << /MonoImageResolution 300 /ColorImageDownsampleType /Average /PreserveEPSInfo false /ColorConversionStrategy /sRGB /GrayImageDownsampleType /Average /EmbedAllFonts true /CannotEmbedFontPolicy /Warning /PreserveOPIComments false /GrayImageResolution 72 /GrayACSImageDict << /ColorTransform 1 /QFactor 0.76 /Blend 1 /HSamples [2 1 1 2] /VSamples [2 1 1 2] >> /ColorImageResolution 72 /PreserveOverprintSettings false /CreateJobTicket false /AutoRotatePages /PageByPage /MonoImageDownsampleType /Average /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] /ColorACSImageDict << /ColorTransform 1 /QFactor 0.76 /Blend 1 /HSamples [2 1 1 2] /VSamples [2 1 1 2] >> /CompatibilityLevel 1.3 /UCRandBGInfo /Remove /DoThumbnails false >>
/printer << /MonoImageResolution 1200 /ColorImageDownsampleType /Bicubic /PreserveEPSInfo true /ColorConversionStrategy /UseDeviceIndependentColor /GrayImageDownsampleType /Bicubic /EmbedAllFonts true /CannotEmbedFontPolicy /Warning /PreserveOPIComments true /GrayImageResolution 300 /GrayACSImageDict << /ColorTransform 1 /QFactor 0.4 /Blend 1 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageResolution 300 /PreserveOverprintSettings true /CreateJobTicket true /AutoRotatePages /None /MonoImageDownsampleType /Bicubic /NeverEmbed [] /ColorACSImageDict << /ColorTransform 1 /QFactor 0.4 /Blend 1 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /CompatibilityLevel 1.4 /UCRandBGInfo /Preserve /DoThumbnails false >>
/default << /DoThumbnails false /PreserveEPSInfo true /ColorConversionStrategy /LeaveColorUnchanged /DownsampleMonoImages false /EmbedAllFonts true /CannotEmbedFontPolicy /Warning /PreserveOPIComments true /GrayACSImageDict << /VSamples [2 1 1 2] /QFactor 0.9 /Blend 1 /HSamples [2 1 1 2] >> /DownsampleColorImages false /PreserveOverprintSettings true /CreateJobTicket false /AutoRotatePages /PageByPage /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] /ColorACSImageDict << /VSamples [2 1 1 2] /QFactor 0.9 /Blend 1 /HSamples [2 1 1 2] >> /DownsampleGrayImages false /UCRandBGInfo /Preserve /Optimize false >>
$ time pdfopt *******.pdf *******-pdfopt.pdf **** Considering object with an invalid number 11997 as null. **** Considering object with an invalid number 11998 as null. **** Considering object with an invalid number 11997 as null. **** Considering object with an invalid number 11998 as null. real 1m28.014s user 0m14.029s sys 0m10.089s $ pdfinfo *******-pdfopt.pdf Creator: pdftk 2.01 - www.pdftk.com Producer: itext-paulo-155 (itextpdf.sf.net-lowagie.com) CreationDate: Fri Mar 14 16:44:32 2014 ModDate: Fri Mar 14 16:44:32 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 149536440 bytes Optimized: no PDF version: 1.7
$ time pdftk *******.pdf cat output *******-pdftk.pdf compress real 1m0.180s user 0m8.469s sys 0m10.385s $ pdfinfo *******-pdftk.pdf Creator: pdftk 1.44 - www.pdftk.com Producer: itext-paulo-155 (itextpdf.sf.net-lowagie.com) CreationDate: Sat Mar 15 02:33:44 2014 ModDate: Sat Mar 15 02:33:44 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 147370039 bytes Optimized: no PDF version: 1.4
$ time qpdf --linearize *******.pdf *******-qpdf.pdf real 1m23.840s user 0m33.274s sys 0m6.624s $ pdfinfo *******-qpdf.pdf Creator: pdftk 2.01 - www.pdftk.com Producer: itext-paulo-155 (itextpdf.sf.net-lowagie.com) CreationDate: Fri Mar 14 16:44:32 2014 ModDate: Fri Mar 14 16:44:32 2014 Tagged: no Pages: 238 Encrypted: no Page size: 595.276 x 785.197 pts File size: 148749860 bytes Optimized: yes PDF version: 1.7