pdf: PDF Graphics Device

PDF Graphics Device

Description

pdf starts the graphics device driver for producing PDF graphics.

Usage

pdf(file = if(onefile) "Rplots.pdf" else "Rplot%03d.pdf",
    width, height, onefile, family, title, fonts, version,
    paper, encoding, bg, fg, pointsize, pagecentre, colormodel,
    useDingbats, useKerning, fillOddEven, compress)

Arguments

Details

All arguments except file default to values given by pdf.options(). The ultimate defaults are quoted in the arguments section.

pdf() opens the file file and the PDF commands needed to plot any graphics requested are sent to that file.

The file argument is interpreted as a C integer format as used by sprintf, with integer argument the page number. The default gives files ‘Rplot001.pdf’, ..., ‘Rplot999.pdf’, ‘Rplot1000.pdf’, ....

The family argument can be used to specify a PDF-specific font family as the initial/default font for the device. If additional font families are to be used they should be included in the fonts argument.

If a device-independent R graphics font family is specified (e.g., via par(family = ) in the graphics package), the PDF device makes use of the PostScript font mappings to convert the R graphics font family to a PDF-specific font family description. (See the documentation for pdfFonts.)

This device does not embed fonts in the PDF file, so it is only straightforward to use mappings to the font families that can be assumed to be available in any PDF viewer: "Times" (equivalently "serif"), "Helvetica" (equivalently "sans") and "Courier" (equivalently "mono"). Other families may be specified, but it is the user's responsibility to ensure that these fonts are available on the system and third-party software (e.g., Ghostscript) may be required to embed the fonts so that the PDF can be included in other documents (e.g., LaTeX): see embedFonts. The URW-based families described for postscript can be used with viewers, platform dependently:

on Unix-alikes

viewers set up to use URW fonts, which is usual with those based on xpdf or Ghostscript.

on Windows

viewers such as GSView which utilise URW fonts.

Since embedFonts makes use of Ghostscript, it should be able to embed the URW-based families for use with other viewers.

See postscript for details of encodings, as the internal code is shared between the drivers. The native PDF encoding is given in file ‘PDFDoc.enc’.

The PDF produced is fairly simple, with each page being represented as a single stream (by default compressed and possibly with references to raster images). The R graphics model does not distinguish graphics objects at the level of the driver interface.

The version argument declares the version of PDF that gets produced. The version must be at least 1.2 when compression is used, 1.4 for semi-transparent output to be understood, and at least 1.3 if CID fonts are to be used: if any of these features are used the version number will be increased (with a warning). (PDF 1.4 was first supported by Acrobat 5 in 2001; it is very unlikely not to be supported in a current viewer.)

Line widths as controlled by par(lwd = ) are in multiples of 1/96 inch. Multiples less than 1 are allowed. pch = "." with cex = 1 corresponds to a square of side 1/72 inch, which is also the ‘pixel’ size assumed for graphics parameters such as "cra".

The paper argument sets the /MediaBox entry in the file, which defaults to width by height. If it is set to something other than "special", a device region of the specified size is (by default) centred on the rectangle given by the paper size: if either width or height is less than 0.1 or too large to give a total margin of 0.5 inch, it is reset to the corresponding paper dimension minus 0.5. Thus if you want the default behaviour of postscript use pdf(paper = "a4r", width = 0, height = 0) to centre the device region on a landscape A4 page with 0.25 inch margins.

When the background colour is fully transparent (as is the initial default value), the PDF produced does not paint the background. Most PDF viewers will use a white canvas so the visual effect is if the background were white. This will not be the case when printing onto coloured paper, though.

Color models

The default color model ("srgb") is sRGB. Model "gray" (or "grey") maps sRGB colors to greyscale using perceived luminosity (biased towards green). "cmyk" outputs in CMYK colorspace. The simplest possible conversion from sRGB to CMYK is used (https://en.wikipedia.org/wiki/CMYK_color_model#Mapping_RGB_to_CMYK), and raster images are output in RGB.

Also available for backwards compatibility is model "rgb" which uses uncalibrated RGB and corresponds to the model used with that name in R prior to 2.13.0. Some viewers may render some plots in that colorspace faster than in sRGB, and the plot files will be smaller.

Conventions

This section describes the implementation of the conventions for graphics devices set out in the ‘R Internals’ manual.

• The default device size is 7 inches square.

• Font sizes are in big points.

• The default font family is Helvetica.

• Line widths are as a multiple of 1/96 inch, with a minimum of 0.01 enforced.

• Circles of any radius are allowed. If useDingbats = TRUE, opaque circles of less than 10 big points radius are rendered using char 108 in the Dingbats font: all semi-transparent and larger circles using a Bézier curve for each quadrant.

• Colours are by default specified as sRGB.

At very small line widths, the line type may be forced to solid.

Printing

Except on Windows it is possible to print directly from pdf by something like (this is appropriate for a CUPS printing system):

    pdf("|lp -o landscape", paper = "a4r")

This forces onefile = TRUE.

Note

If you see problems with PDF output, do remember that the problem is much more likely to be in your viewer than in R. Try another viewer if possible. Symptoms for which the viewer has been at fault are apparent grids on image plots (turn off graphics anti-aliasing in your viewer if you can) and missing or incorrect glyphs in text (viewers silently doing font substitution).

Unfortunately the default viewers on most Linux and macOS systems have these problems, and no obvious way to turn off graphics anti-aliasing.

Acrobat Reader does not use the fonts specified but rather emulates them from multiple-master fonts. This can be seen in imprecise centering of characters, for example the multiply and divide signs in Helvetica. This can be circumvented by embedding fonts where possible. Most other viewers substitute fonts, e.g. URW fonts for the standard Helvetica and Times fonts, and these too often have different font metrics from the true fonts.

Acrobat Reader can be extended by ‘font packs’, and these will be needed for the full use of encodings other than Latin-1 (although they may be offered for download as needed).

On some Unix-alike systems:

If useDingbats = TRUE, the default plotting character pch = 1 was displayed in some PDF viewers incorrectly as a "q" character. (These seem to be viewers based on the poppler PDF rendering library). This may be due to incorrect or incomplete mapping of font names to those used by the system. Adding the following lines to ‘~/.fonts.conf’ or ‘/etc/fonts/local.conf’ may circumvent this problem, although this has largely been corrected on the affected systems.

<fontconfig>
<alias binding="same">
  <family>ZapfDingbats</family>
  <accept><family>Dingbats</family></accept>
</alias>
</fontconfig>

Some further workarounds for problems with symbol fonts on viewers using ‘fontconfig’ are given in the ‘Cairo Fonts’ section of the help for X11.

On Windows:

The TeXworks PDF viewer was one of those which has been seen to fail to display Dingbats (used by e.g. pch = 1) correctly. Whereas on other platforms the problems seen were incorrect output, on Windows points were silently omitted: however recent versions seem to manage to display Dingbats.

There was a different font bug in the pdf.js viewer included in Firefox: that mapped Dingbats to the Symbol font and so displayed symbols such pch = 1 as lambda.

See Also

pdfFonts, pdf.options, embedFonts, Devices, postscript.

cairo_pdf and (on macOS only) quartz for other devices that can produce PDF.

More details of font families and encodings and especially handling text in a non-Latin-1 encoding and embedding fonts can be found in

Paul Murrell and Brian Ripley (2006). “Non-standard fonts in PostScript and PDF graphics.” R News, 6(2), 41–47. https://www.r-project.org/doc/Rnews/Rnews_2006-2.pdf.

Examples

## Test function for encodings
TestChars <- function(encoding = "ISOLatin1", ...)
{
    pdf(encoding = encoding, ...)
    par(pty = "s")
    plot(c(-1,16), c(-1,16), type = "n", xlab = "", ylab = "",
         xaxs = "i", yaxs = "i")
         title(paste("Centred chars in encoding", encoding))
    grid(17, 17, lty = 1)
    for(i in c(32:255)) {
        x <- i %% 16
        y <- i %/% 16
        points(x, y, pch = i)
    }
    dev.off()
}
## there will be many warnings.
TestChars("ISOLatin2")
## this does not view properly in older viewers.
TestChars("ISOLatin2", family = "URWHelvetica")
## works well for viewing in gs-based viewers, and often in xpdf.