PostScript Graphics

Description

postscript starts the graphics device driver for producing PostScript graphics.

Usage

postscript(file = if(onefile) "Rplots.ps" else "Rplot%03d.ps",
           onefile, family, title, fonts, encoding, bg, fg,
           width, height, horizontal, pointsize,
           paper, pagecentre, print.it, command,
           colormodel, useKerning, fillOddEven)

Arguments

Details

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

postscript opens the file file and the PostScript commands needed to plot any graphics requested are written to that file. This file can then be printed on a suitable device to obtain hard copy.

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.ps’, ..., ‘Rplot999.ps’, ‘Rplot1000.ps’, ....

The postscript produced for a single R plot is EPS (Encapsulated PostScript) compatible, and can be included into other documents, e.g., into LaTeX, using \includegraphics{<filename>}. For use in this way you will probably want to use setEPS() to set the defaults as horizontal = FALSE, onefile = FALSE, paper = "special". Note that the bounding box is for the device region: if you find the white space around the plot region excessive, reduce the margins of the figure region via par(mar = ).

Most of the PostScript prologue used is taken from the R character vector .ps.prolog. This is marked in the output, and can be changed by changing that vector. (This is only advisable for PostScript experts: the standard version is in namespace:grDevices.)

A PostScript device has a default family, which can be set by the user via family. If other font families are to be used when drawing to the PostScript device, these must be declared when the device is created via fonts; the font family names for this argument are R graphics font family names (see the documentation for postscriptFonts).

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".

When the background colour is fully transparent (as is the initial default value), the PostScript produced does not paint the background. Almost all PostScript 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.

Families

Font families are collections of fonts covering the five font faces, (conventionally plain, bold, italic, bold-italic and symbol) selected by the graphics parameter par(font = ) or the grid parameter gpar(fontface = ). Font families can be specified either as an an initial/default font family for the device via the family argument or after the device is opened by the graphics parameter par(family = ) or the grid parameter gpar(fontfamily = ). Families which will be used in addition to the initial family must be specified in the fonts argument when the device is opened.

Font families are declared via a call to postscriptFonts.

The argument family specifies the initial/default font family to be used. In normal use it is one of "AvantGarde", "Bookman", "Courier", "Helvetica", "Helvetica-Narrow", "NewCenturySchoolbook", "Palatino" or "Times", and refers to the standard Adobe PostScript fonts families of those names which are included (or cloned) in all common PostScript devices.

Many PostScript emulators (including those based on ghostscript) use the URW equivalents of these fonts, which are "URWGothic", "URWBookman", "NimbusMon", "NimbusSan", "NimbusSanCond", "CenturySch", "URWPalladio" and "NimbusRom" respectively. If your PostScript device is using URW fonts, you will obtain access to more characters and more appropriate metrics by using these names. To make these easier to remember, "URWHelvetica" == "NimbusSan" and "URWTimes" == "NimbusRom" are also supported.

Another type of family makes use of CID-keyed fonts for East Asian languages – see postscriptFonts.

The family argument is normally a character string naming a font family, but family objects generated by Type1Font and CIDFont are also accepted. For compatibility with earlier versions of R, the initial family can also be specified as a vector of four or five afm files.

Note that R does not embed the font(s) used in the PostScript output: see embedFonts for a utility to help do so.

Viewers and embedding applications frequently substitute fonts for those specified in the family, and the substitute will often have slightly different font metrics. useKerning = TRUE spaces the letters in the string using kerning corrections for the intended family: this may look uglier than useKerning = FALSE.

Encodings

Encodings describe which glyphs are used to display the character codes (in the range 0–255). Most commonly R uses ISOLatin1 encoding, and the examples for text are in that encoding. However, the encoding used on machines running R may well be different, and by using the encoding argument the glyphs can be matched to encoding in use. This suffices for European and Cyrillic languages, but not for East Asian languages. For the latter, composite CID fonts are used. These fonts are useful for other languages: for example they may contain Greek glyphs. (The rest of this section applies only when CID fonts are not used.)

None of this will matter if only ASCII characters (codes 32–126) are used as all the encodings (except "TeXtext") agree over that range. Some encodings are supersets of ISOLatin1, too. However, if accented and special characters do not come out as you expect, you may need to change the encoding. Some other encodings are supplied with R: "WinAnsi.enc" and "MacRoman.enc" correspond to the encodings normally used on Windows and Classic Mac OS (at least by Adobe), and "PDFDoc.enc" is the first 256 characters of the Unicode encoding, the standard for PDF. There are also encodings "ISOLatin2.enc", "CP1250.enc", "ISOLatin7.enc" (ISO 8859-13), "CP1257.enc", and "ISOLatin9.enc" (ISO 8859-15), "Cyrillic.enc" (ISO 8859-5), "KOI8-R.enc", "KOI8-U.enc", "CP1251.enc", "Greek.enc" (ISO 8859-7) and "CP1253.enc". Note that many glyphs in these encodings are not in the fonts corresponding to the standard families. (The Adobe ones for all but Courier, Helvetica and Times cover little more than Latin-1, whereas the URW ones also cover Latin-2, Latin-7, Latin-9 and Cyrillic but no Greek. The Adobe exceptions cover the Latin character sets, but not the Euro.)

If you specify the encoding, it is your responsibility to ensure that the PostScript font contains the glyphs used. One issue here is the Euro symbol which is in the WinAnsi and MacRoman encodings but may well not be in the PostScript fonts. (It is in the URW variants; it is not in the supplied Adobe Font Metric files.)

There is an exception. Character 45 ("-") is always set as minus (its value in Adobe ISOLatin1) even though it is hyphen in the other encodings. Hyphen is available as character 173 (octal 0255) in all the Latin encodings, Cyrillic and Greek. (This can be entered as "\uad" in a UTF-8 locale.) There are some discrepancies in accounts of glyphs 39 and 96: the supplied encodings (except CP1250 and CP1251) treat these as ‘quoteright’ and ‘quoteleft’ (rather than ‘quotesingle’/‘acute’ and ‘grave’ respectively), as they are in the Adobe documentation.

TeX fonts

TeX has traditionally made use of fonts such as Computer Modern which are encoded rather differently, in a 7-bit encoding. This encoding can be specified by encoding = "TeXtext.enc", taking care that the ASCII characters < > \ _ { } are not available in those fonts.

There are supplied families "ComputerModern" and "ComputerModernItalic" which use this encoding, and which are only supported for postscript (and not pdf). They are intended to use with the Type 1 versions of the TeX CM fonts. It will normally be possible to include such output in TeX or LaTeX provided it is processed with dvips -Ppfb -j0 or the equivalent on your system. (-j0 turns off font subsetting.) When family = "ComputerModern" is used, the italic/bold-italic fonts used are slanted fonts (cmsl10 and cmbxsl10). To use text italic fonts instead, set family = "ComputerModernItalic".

These families use the TeX math italic and symbol fonts for a comprehensive but incomplete coverage of the glyphs covered by the Adobe symbol font in other families. This is achieved by special-casing the postscript code generated from the supplied ‘CM_symbol_10.afm’.

Color models

The default color model ("srgb") is sRGB.

The alternative "srgb+gray" uses sRGB for colors, but with pure gray colors (including black and white) expressed as greyscales (which results in smaller files and can be advantageous with some printer drivers). Conversely, its files can be rendered much slower on some viewers, and there can be a noticeable discontinuity in color gradients involving gray or white.

Other possibilities are "gray" (or "grey") which used only greyscales (and converts other colours to a luminance), and "cmyk". 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.

Color models provided for backwards compatibility are "rgb") (which is RGB+gray) and "rgb-nogray" which use uncalibrated RGB (as used in R prior to 2.13.0). These result in slightly smaller files which may render faster, but do rely on the viewer being properly calibrated.

Printing

A postscript plot can be printed via postscript in two ways.

1. Setting print.it = TRUE causes the command given in argument command to be called with argument "file" when the device is closed. Note that the plot file is not deleted unless command arranges to delete it.

2. file = "" or file = "|cmd" can be used to print using a pipe. Failure to open the command will probably be reported to the terminal but not to R, in which case close the device by dev.off immediately.

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.

• Circle of any radius are allowed.

• Colours are by default specified as sRGB.

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

Raster images are currently limited to opaque colours.

Note

If you see problems with postscript 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.

Author(s)

Support for Computer Modern fonts is based on a contribution by Brian D'Urso durso@hussle.harvard.edu.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

postscriptFonts, Devices, and check.options which is called from both ps.options and postscript.

cairo_ps for another device that can produce PostScript.

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

require(graphics)
## Not run: 
# open the file "foo.ps" for graphics output
postscript("foo.ps")
# produce the desired graph(s)
dev.off()              # turn off the postscript device
postscript("|lp -dlw")
# produce the desired graph(s)
dev.off()              # plot will appear on printer

# for URW PostScript devices
postscript("foo.ps", family = "NimbusSan")

## for inclusion in Computer Modern TeX documents, perhaps
postscript("cm_test.eps", width = 4.0, height = 3.0,
           horizontal = FALSE, onefile = FALSE, paper = "special",
           family = "ComputerModern", encoding = "TeXtext.enc")
## The resultant postscript file can be used by dvips -Ppfb -j0.

## To test out encodings, you can use
TestChars <- function(encoding = "ISOLatin1", family = "URWHelvetica")
{
    postscript(encoding = encoding, family = family)
    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.  We use URW to get a complete enough
## set of font metrics.
TestChars()
TestChars("ISOLatin2")
TestChars("WinAnsi")

## End(Not run)