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tools (version 3.3)

compactPDF: Compact PDF Files

Description

Re-save PDF files (especially vignettes) more compactly. Support function for R CMD build --compact-vignettes.

Usage

compactPDF(paths,
           qpdf = Sys.which(Sys.getenv("R_QPDF", "qpdf")),
           gs_cmd = Sys.getenv("R_GSCMD", ""),
           gs_quality = Sys.getenv("GS_QUALITY", "none"),
           gs_extras = character())
## S3 method for class 'compactPDF':
format(x, ratio = 0.9, diff = 1e4, ...)

Arguments

paths
A character vector of paths to PDF files, or a length-one character vector naming a directory, when all .pdf files in that directory will be used.
qpdf
Character string giving the path to the qpdf command. If empty, qpdf will not be used.
gs_cmd
Character string giving the path to the GhostScript executable, if that is to be used. On Windows this is the path to gswin32c.exe or gswin64c.exe. If "" (the default), the function will try to find a platform-specific path to GhostScript where required.
gs_quality
A character string indicating the quality required: the options are "none" (so GhostScript is not used), "printer" (300dpi), "ebook" (150dpi) and "screen" (72dpi). Can be abbreviated.
gs_extras
An optional character vector of further options to be passed to GhostScript.
x
An object of class "compactPDF".
ratio, diff
Limits for reporting: files are only reported whose sizes are reduced both by a factor of ratio and by diff bytes.
...
Further arguments to be passed to or from other methods.

Value

  • An object of class c("compactPDF", "data.frame"). This has two columns, the old and new sizes in bytes for the files that were changed.

    There are format and print methods: the latter passes ... to the format method, so will accept ratio and diff arguments.

Details

This by default makes use of qpdf, available from http://qpdf.sourceforge.net/ (including as a Windows binary) and included with the CRAN OS X distribution of R. If gs_cmd is non-empty and gs_quality != "none", GhostScript will used first, then qpdf if it is available. If gs_quality != "none" and gs_cmd is "", an attempt will be made to find a GhostScript executable.

qpdf and/or gs_cmd are run on all PDF files found, and those which are reduced in size by at least 10% and 10Kb are replaced.

The strategy of our use of qpdf is to (losslessly) compress both PDF streams and objects. GhostScript compresses streams and more (including downsampling and compressing embedded images) and consequently is much slower and may lose quality (but can also produce much smaller PDF files). However, quality "ebook" is perfectly adequate for screen viewing and printing on laser printers.

Where PDF files are changed they will become PDF version 1.5 files: these have been supported by Acrobat Reader since version 6 in 2003, so this is very unlikely to cause difficulties.

Stream compression is what most often has large gains. Most PDF documents are generated with object compression, but this does not seem to be the default for MiKTeX's pdflatex. For some PDF files (and especially package vignettes), using GhostScript can dramatically reduce the space taken by embedded images (often screenshots).

Where both GhostScript and qpdf are selected (when gs_quality != "none" and both executables are found), they are run in that order and the size reductions apply to the total compression achieved.

See Also

resaveRdaFiles.

Many other (and sometimes more effective) tools to compact PDF files are available, including Adobe Acrobat (not Reader). See the Writing R Extensions manual.