dev2bitmap: Graphics Device for Bitmap Files via Ghostscript

Description

bitmap generates a graphics file. dev2bitmap copies the current graphics device to a file in a graphics format.

Usage

bitmap(file, type = "png16m", height = 7, width = 7, res = 72, units = "in", pointsize, taa = NA, gaa = NA, ...)
dev2bitmap(file, type = "png16m", height = 7, width = 7, res = 72, units = "in", pointsize, ..., method = c("postscript", "pdf"), taa = NA, gaa = NA)

Arguments

file

The output file name, with an appropriate extension.

type

The type of bitmap.

width, height

Dimensions of the display region.

res

Resolution, in dots per inch.

units

The units in which height and width are given. Can be in (inches), px (pixels), cm or mm.

pointsize

The pointsize to be used for text: defaults to something reasonable given the width and height

...

Other parameters passed to postscript or pdf.

method

Should the plot be done by postscript or pdf?

taa, gaa

Number of bits of antialiasing for text and for graphics respectively. Usually 4 (for best effect) or 2. Not supported on all types.

Value

None.

Conventions

This section describes the implementation of the conventions for graphics devices set out in the “R Internals Manual”. These devices follow the underlying device, so when viewed at the stated res:

The default device size is 7 inches square.
Font sizes are in big points.
The default font family is (for the standard Ghostscript setup) URW Nimbus Sans.
Line widths are as a multiple of 1/96 inch, with no minimum.
Circle of any radius are allowed.
Colours are interpreted by the viewing/printing application.

Details

dev2bitmap works by copying the current device to a postscript or pdf device, and post-processing the output file using ghostscript. bitmap works in the same way using a postscript device and post-processing the output as ‘printing’.

You will need ghostscript: the full path to the executable can be set by the environment variable R_GSCMD. If this is unset, a GhostScript executable will be looked for by name on your path: on a Unix alike "gs" is used, and on Windows the setting of the environment variable GSC is used, otherwise commands "gswi64c.exe" then "gswin32c.exe" are tried.

The types available will depend on the version of ghostscript, but are likely to include "jpeg", "jpegcmyk", "jpeggray", "tiffcrle", "tiffg3", "tiffg32d", "tiffg4", "tiffgray", "tifflzw", "tiffpack", "tiff12nc", "tiff24nc", "tiff32nc" "png16", "png16m", "png256", "png48", "pngmono", "pnggray", "pngalpha", "bmp16", "bmp16m" "bmp256", "bmp32b", "bmpgray", "bmpmono".

The default type, "png16m", supports 24-bit colour and anti-aliasing. Type "png256" uses a palette of 256 colours and could give a more compact representation. Monochrome graphs can use "pngmono", or "pnggray" if anti-aliasing is desired. Plots with a transparent background and varying degrees of transparency should use "pngalpha".

Note that for a colour TIFF image you probably want "tiff24nc", which is 8-bit per channel RGB (the most common TIFF format). None of the listed TIFF types support transparency. "tiff32nc" uses 8-bit per channel CMYK, which printers might require.

For formats which contain a single image, a file specification like Rplots%03d.png can be used: this is interpreted by Ghostscript.

For dev2bitmap if just one of width and height is specified, the other is chosen to preserve the aspect ratio of the device being copied. The main reason to prefer method = "pdf" over the default would be to allow semi-transparent colours to be used.

For graphics parameters such as "cra" that need to work in pixels, the default resolution of 72dpi is always used.

windows Paths for file and R_GSCMD which contain spaces are mapped to short names via shortPathName.