R: BMP, JPEG, PNG and TIFF graphics devices

png {grDevices} | R Documentation

## BMP, JPEG, PNG and TIFF graphics devices

### Description

Graphics devices for BMP, JPEG, PNG and 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", "cairo-png", "Xlib", "quartz"), antialias)

    tiff(filename = "Rplot%03d.tiff",
         width = 480, height = 480, units = "px", pointsize = 12,
         compression = c("none", "rle", "lzw", "jpeg", "zip", "lzw+p", "zip+p"),
         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` ppi.
`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. Ignored for `type = "quartz"`.
`res` | The nominal resolution in ppi 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 `fonts` or `family`. For types `"cairo"` and `"quartz"`, the `family` argument can be supplied. See the ‘Cairo fonts’ section in the help for `X11`.
`type` | character string, one of `"Xlib"` or `"quartz"` (some 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 for fonts and lines (but not fills). See `X11`. The default is set by `X11.options`. Also for `type = "quartz"`, where antialiasing is used unless `antialias = "none"`.

### 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 appears as transparent if used in the plot. This allows opaque white to be used, as in the example. The `type = "cairo"`, `type = "cairo-png"` and `type = "quartz"` variants allow semi-transparent colours, including on a transparent or semi-transparent background.

`tiff` with types `"cairo"` and `"quartz"` supports semi-transparent colours, including on a transparent or semi-transparent background. Compression type `"zip"` is ‘deflate (Adobe-style)’. Compression types `"lzw+p"` and `"zip+p"` use horizontal differencing (‘differencing predictor’, section 14 of the TIFF specification) in combination with the compression method, which is effective for continuous-tone images, especially colour ones.

R can be compiled without support for some or all of the types 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 OS X builds: see `capabilities("aqua")`).

By default no resolution is recorded in the file, except for BMP. Viewers will often assume a nominal resolution of 72 ppi when none is recorded. As resolutions in PNG files are recorded in pixels/metre, the reported ppi 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 72 ppi if unset).

`png` will normally 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 ARGB file if `type = "cairo"` and non-opaque colours are used). However, `type = "cairo-png"` uses cairographics' PNG backend which will never use a palette and normally creates a larger 32-bit ARGB file—this may work better for specialist uses with semi-transparent colours.

Quartz-produced PNG and TIFF plots with a transparent background are recorded with a dark grey matte which will show up in some viewers, including `Preview` on OS X.

Prior to R 3.0.3 unknown resolutions in BMP files were sometimes recorded incorrectly: they are now recorded as 72 ppi.

### Value

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

### Warnings

Note that by default the `width` and `height` values 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.

### Differences between OSes

These functions are interfaces to three or more different underlying devices.

- On Windows, devices based on plotting to a hidden screen using Windows' GDI calls.

- On platforms with support for X11, plotting to a hidden X11 display.

- On OS X when working at the console and when R is compiled with suitable support, using Apple's Quartz plotting system.

- Where support has been compiled in for cairographics, plotting on cairo surfaces. This may use the native platform support for fonts, or it may use `fontconfig` to support a wide range of font formats. (This was first available on Windows in R 2.14.0.)

Inevitably there will be differences between the options supported and output produced. Perhaps the most important are support for antialiased fonts and semi-transparent colours: the best results are likely to be obtained with the cairo- or Quartz-based devices where available.

The default extensions are ‘.jpg’ and ‘.tif’ on Windows, and ‘.jpeg’ and ‘.tiff’ elsewhere.

### 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` ppi.

- The default font family is Helvetica.

- Line widths in 1/96 inch (interpreted at `res` ppi), 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

### References

The PNG specification, http://www.w3.org/TR/PNG/.

The TIFF specification, including extensions, at http://partners.adobe.com/public/developer/tiff/.

### 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 plots in many bitmap formats that does not depend on accessing the X11 display but does depend on having GhostScript installed.

### Examples

    ## these examples will work only if the devices are available
    ## and cairo or an X11 display or an 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)

    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 3.1.2 Index]