Skip to Content

png {grDevices}

BMP, JPEG, PNG and TIFF graphics devices
Package: 
grDevices
Version: 
R 2.12.1

Description

Graphics devices for JPEG, PNG or TIFF format bitmap files.

Usage

bmp(filename = "Rplot%03d.bmp",
    width = 480, height = 480, units = "px",
    pointsize = 12, bg = "white", res = NA, ...,
    type = c("cairo", "Xlib", "quartz"), antialias)

jpeg(filename = "Rplot%03d.jpeg",
     width = 480, height = 480, units = "px",
     pointsize = 12, quality = 75, bg = "white", res = NA, ...,
     type = c("cairo", "Xlib", "quartz"), antialias)

png(filename = "Rplot%03d.png",
    width = 480, height = 480, units = "px",
    pointsize = 12, bg = "white",  res = NA, ...,
    type = c("cairo", "Xlib", "quartz"), antialias)

tiff(filename = "Rplot%03d.tiff",
     width = 480, height = 480, units = "px", pointsize = 12,
     compression = c("none", "rle", "lzw", "jpeg", "zip"),
     bg = "white", res = NA,  ...,
     type = c("cairo", "Xlib", "quartz"), antialias)

Arguments

filename
the name of the output file. The page number is substituted if a C integer format is included in the character string, as in the default. (The result must be less than PATH_MAX characters long, and may be truncated if not. See postscript for further details.) Tilde expansion is performed where supported by the platform.
width
the width of the device.
height
the height of the device.
units
The units in which height and width are given. Can be px (pixels, the default), in (inches), cm or mm.
pointsize
the default pointsize of plotted text, interpreted as big points (1/72 inch) at res dpi.
bg
the initial background colour: can be overridden by setting par("bg").
quality
the ‘quality’ of the JPEG image, as a percentage. Smaller values will give more compression but also more degradation of the image.
compression
the type of compression to be used.
res
The nominal resolution in dpi which will be recorded in the bitmap file, if a positive integer. Also used for units other than the default, and to convert points to pixels.
...
for type = "Xlib" only, additional arguments to the underlying X11 device, such as gamma and fonts.
type
character string, one of "Xlib" or "quartz" (some Mac OS X builds) or "cairo". The latter will only be available if the system was compiled with support for cairo -- otherwise "Xlib" will be used. The default is set by getOption("bitmapType") -- the ‘out of the box’ default is "quartz" or "cairo" where available, otherwise "Xlib".
antialias
for type = "cairo", giving the type of anti-aliasing (if any) to be used. See X11. The default is set by X11.options.

Details

Plots in PNG and JPEG format can easily be converted to many other bitmap formats, and both can be displayed in modern web browsers. The PNG format is lossless and is best for line diagrams and blocks of colour. The JPEG format is lossy, but may be useful for image plots, for example. BMP is a standard format on Windows. TIFF is a meta-format: the default format written by tiff is lossless and stores RGB (and alpha where appropriate) values uncompressed---such files are widely accepted, which is their main virtue over PNG.

png supports transparent backgrounds: use bg =   "transparent". Not all PNG viewers render files with transparency correctly. When transparency is in use in the type = "Xlib" variant a very light grey is used as the background and so appear as transparent if used in the plot. This allows opaque white to be used, as in the example. The type = "cairo" and type =   "cairo1" variants allows semi-transparent colours, including on a transparent or semi-transparent background.

tiff(type = "cairo") supports semi-transparent colours, including on a transparent or semi-transparent background.

R can be compiled without support for each of these devices: this will be reported if you attempt to use them on a system where they are not supported. For type = "Xlib" they may not be usable unless the X11 display is available to the owner of the R process. type = "cairo" requires cairo 1.2 or later. type =   "quartz" uses the quartz device and so is only available where that is (on some Mac OS X builds: see capabilities("aqua")).

By default no resolution is recorded in the file. Viewers will often assume a nominal resolution of 72dpi when none is recorded. As resolutions in PNG files are recorded in pixels/metre, the reported dpi value will be changed slightly.

For graphics parameters that make use of dimensions in inches (including font sizes in points) the resolution used is res (or 72dpi if unset).

png will use a palette if there are less than 256 colours on the page, and record a 24-bit RGB file otherwise (or a 32-bit RGBA file if type = "cairo" and non-opaque colours are used).

Values

A plot device is opened: nothing is returned to the R interpreter.

Warnings

Note that by default the width and height are in pixels not inches. A warning will be issued if both are less than 20.

If you plot more than one page on one of these devices and do not include something like %d for the sequence number in file, the file will contain the last page plotted.

Conventions

This section describes the implementation of the conventions for graphics devices set out in the “R Internals Manual”.

  • The default device size is in pixels.
  • Font sizes are in big points interpreted at res dpi.
  • The default font family is Helvetica.
  • Line widths in 1/96 inch, minimum one pixel for type =       "Xlib", 0.01 for type = "cairo".
  • For type = "Xlib" circle radii are in pixels with minimum one.
  • Colours are interpreted by the viewing application.

For type = "quartz" see the help for quartz.

Note

For type = "Xlib" these devices are based on the X11 device. The colour model used will be that set up by X11.options at the time the first Xlib-based devices was opened (or the first after all such devices have been closed).

See Also

Devices, dev.print

capabilities to see if these devices are supported by this build of R, and if type = "cairo" is supported.

bitmap provides an alternative way to generate PNG and JPEG plots that does not depend on accessing the X11 display but does depend on having GhostScript installed. (Devices GDD in CRAN package GDD and CairoJPEG / CairoPNG in CRAN package Cairo are further alternatives using several other additional pieces of software.)

Examples

## these examples will work only if the devices are available
## and cairo or an X11 display or a Mac OS X display is available.
 
## copy current plot to a (large) PNG file
 
## Not run:dev.print(png, file="myplot.png", width=1024, height=768)## End(Not run)
 
 
png(file="myplot.png", bg="transparent")
plot(1:10)
rect(1, 5, 3, 7, col="white")
dev.off()
 
## will make myplot1.jpeg and myplot2.jpeg
jpeg(file="myplot%d.jpeg")
example(rect)
dev.off()

Author(s)

Guido Masarotto and Brian Ripley

Documentation reproduced from R 2.12.1. License: GPL-2.