png {grDevices} | R Documentation

## BMP, JPEG, PNG and TIFF graphics devices

### 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", "cairo1", "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"` (the only type prior to R 2.7.0) or `"quartz"` (some Mac OS X builds) or `"cairo"` or `"cairo1"`. The latter two 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. It is at present experimental.

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).

`png(type = "cairo1")` uses cairo directly to output the file – the resolution is not recorded and the PNG format used is chosen by cairo (and undocumented – it is currently 32-bit RGBA, that is with an alpha channel whether used or not). It is included for use on platforms with cairo 1.0 (where `type = "cairo"` is not available).

### Value

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).

### Author(s)

Guido Masarotto and Brian Ripley

### 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 either cairo or an X11 display is available.

    ## copy current plot to a (large) PNG file
    ## Not run: dev.print(png, file="myplot.png", width=1024, height=768)

    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()

[Package grDevices version 2.8.1 Index]