compactPDF
Compact PDF Files
Re-save PDF files (especially vignettes) more compactly.
Support function for R CMD build --compact-vignettes
.
- Keywords
- utilities
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 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
orgswin64c.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 bydiff
bytes.- …
Further arguments to be passed to or from other methods.
Details
This by default makes use of qpdf
, available from
http://qpdf.sourceforge.net/ (including as a Windows binary) and
included with the CRAN macOS 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.
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.
Note
The external tools used may change in future releases.
Versions of GhostScript 9.06 and later give several times better compression than 9.05 on some vignettes in CRAN packages.
See Also
Many other (and sometimes more effective) tools to compact PDF files are available, including Adobe Acrobat (not Reader). See the ‘Writing R Extensions’ manual.