\HeaderA{png}{BMP, JPEG, PNG and TIFF graphics devices}{png}
\aliasA{bmp}{png}{bmp}
\aliasA{jpeg}{png}{jpeg}
\aliasA{tiff}{png}{tiff}
\keyword{device}{png}
\begin{Description}\relax
Graphics devices for JPEG, PNG or TIFF format bitmap files.
\end{Description}
\begin{Usage}
\begin{verbatim}
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)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{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 \code{PATH\_MAX} characters long, and may be truncated if not.
See \code{\LinkA{postscript}{postscript}} for further details.)  Tilde expansion
is performed where supported by the platform.
\item[\code{width}] the width of the device.
\item[\code{height}] the height of the device.
\item[\code{units}] The units in which \code{height} and \code{width} are
given.  Can be \code{px} (pixels, the default), \code{in} (inches),
\code{cm} or \code{mm}.
\item[\code{pointsize}] the default pointsize of plotted text, interpreted as
big points (1/72 inch) at \code{res} dpi.
\item[\code{bg}] the initial background colour: can be overridden by setting
par("bg").
\item[\code{quality}] the \sQuote{quality} of the JPEG image, as a
percentage.  Smaller values will give more compression but also more
degradation of the image.
\item[\code{compression}] the type of compression to be used.
\item[\code{res}] The nominal resolution in dpi which will be recorded in the
bitmap file, if a positive integer.  Also used for \code{units}
other than the default, and to convert points to pixels.
\item[\code{...}] for \code{type = "Xlib"} only, additional arguments to
the underlying \code{\LinkA{X11}{X11}} device, such as \code{gamma} and
\code{fonts}.
\item[\code{type}] character string, one of \code{"Xlib"} (the only type
prior to \R{} 2.7.0) or \code{"quartz"} or \code{"cairo"} or
\code{"cairo1"}.  The latter two will only be available if the
system was compiled with support for cairo -- otherwise
\code{"Xlib"} will be used.  The default is set by
\code{\LinkA{getOption}{getOption}("bitmapType")} -- the \sQuote{out of thebox}
default is \code{"quartz"} or \code{"cairo"} where available,
otherwise \code{"Xlib"}.
\item[\code{antialias}] for \code{type = "cairo"}, giving the type of
anti-aliasing (if any) to be used.  See \code{\LinkA{X11}{X11}}.  The
default is set by \code{\LinkA{X11.options}{X11.options}}.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
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 \code{tiff} is lossless and stores RGB (and alpha where
appropriate) values uncompressed---such files are widely accepted,
which is their main virtue over PNG.   

\code{png} supports transparent backgrounds: use \code{bg =
  "transparent"}.  Not all PNG viewers render files with transparency
correctly.  When transparency is in use in the \code{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 \code{type = "cairo"} and \code{type =
  "cairo1"} variants allows semi-transparent colours, including on a
transparent or semi-transparent background.

\code{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 \code{type = "Xlib"} they may not be usable unless
the X11 display is available to the owner of the \R{} process.  
\code{type = "cairo"} requires cairo 1.2 or later.  \code{type =
  "quartz"} uses the \code{\LinkA{quartz}{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 \code{res} (or
72dpi if unset).

\code{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 \code{type = "cairo"} and non-opaque colours are used).

\code{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 \code{type = "cairo"} is not available).
\end{Details}
\begin{Value}
A plot device is opened: nothing is returned to the \R{} interpreter.
\end{Value}
\begin{Section}{Warnings}
Note that by default the \code{width} and \code{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 \code{\%d} for the sequence number in
\code{file}, the file will contain the last page plotted.
\end{Section}
\begin{Section}{Conventions}
This section describes the implementation of the conventions for
graphics devices set out in the \dQuote{R Internals Manual}.

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

For \code{type = "quartz"} see the help for \code{\LinkA{quartz}{quartz}}.
\end{Section}
\begin{Note}\relax
For \code{type = "Xlib"} these devices are based on the \code{\LinkA{X11}{X11}}
device.  The colour model used will be that set up by
\code{X11.options} at the time the first Xlib-based devices was opened
(or the first after all such devices have been closed).
\end{Note}
\begin{Author}\relax
Guido Masarotto and Brian Ripley
\end{Author}
\begin{SeeAlso}\relax
\code{\LinkA{Devices}{Devices}}, \code{\LinkA{dev.print}{dev.print}}

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

\code{\LinkA{bitmap}{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 \code{GDD} in
CRAN package \pkg{GDD} and \code{CairoJPEG} / \code{CairoPNG} in CRAN
package \pkg{Cairo} are further alternatives using several other
additional pieces of software.)
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
## 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()
\end{ExampleCode}
\end{Examples}

