plot.im.Rd
\name{plot.im}
\alias{plot.im}
\alias{image.im}
\title{Plot a Pixel Image}
\description{
Plot a pixel image.
}
\usage{
\method{plot}{im}(x, \dots, col=NULL,
ribbon=TRUE, ribsep=0.15, ribwid=0.05, ribn=1024)
}
\arguments{
\item{x}{
The pixel image to be plotted.
An object of class \code{"im"} (see \code{\link{im.object}}).
}
\item{\dots}{
Extra arguments passed to \code{\link{image}} to control the plot.
}
\item{col}{
Colours for the pixel values. Either a character vector of colours,
or an object of class \code{\link{colourmap}}.
}
\item{ribbon}{
Logical flag indicating whether to display a ribbon
showing the colour map.
}
\item{ribsep}{
Factor controlling the space between the ribbon and the image.
}
\item{ribwid}{
Factor controlling the width of the ribbon.
}
\item{ribn}{
Number of different values to display in the ribbon.
}
}
\value{
none.
}
\details{
This is the \code{plot} method for the class \code{"im"}.
[It is also the \code{image} method for \code{"im"}.]
The pixel image \code{x} is displayed on the current plot device,
using equal scales on the \code{x} and \code{y} axes.
If \code{ribbon=TRUE}, a legend will be plotted at the right of the
image. The legend consists of a colour ribbon and an axis with tick-marks,
showing the correspondence between the pixel values and the colour map.
Arguments \code{ribsep, ribwid, ribn} control the appearance of the
ribbon.
The width of the ribbon is \code{ribwid} times the size of the pixel
image, where `size' means the larger of the width and the height.
The distance separating the ribbon and the image is \code{ribsep} times
the size of the pixel image. The ribbon contains \code{ribn}
different numerical values, evenly spaced between the minimum and
maximum pixel values in the image \code{x}, rendered according to
the chosen colour map.
The pixel values are displayed using the colours given in the
argument \code{col}. This may be either an explicit colour map
(an object of class \code{"colourmap"}, created by the function
\code{\link{colourmap}}) or a character vector or integer vector
that specifies a set of colours.
If \code{col} is an explicit colour map
(an object of class \code{"colourmap"}) then the same colour
always represents the same numeric value. For example this ensures
that when we plot different images, the colour maps are consistent.
If \code{col} is a character vector or integer vector that specifies
colours, then the colour mapping will be stretched to match the range of
pixel values in the image \code{x}. In this case, the mapping of pixel values
to colours is determined as follows.
\describe{
\item{logical-valued images:}{the values \code{FALSE} and
\code{TRUE} are mapped to the colours \code{col[1]} and
\code{col[2]} respectively.
The vector \code{col} should have length 2.
}
\item{factor-valued images:}{the factor levels \code{levels(x)}
are mapped to the entries of \code{col} in order. The vector
\code{col} should have the same length as \code{levels(x)}.
}
\item{numeric-valued images:}{
By default, the range of pixel values in \code{x}
is divided into \code{n = length(col)}
equal subintervals, which are mapped to the colours in \code{col}.
(If \code{col} was not specified, it defaults to a vector of 255
colours.)
Alternatively if the argument \code{zlim} is given, it should be
a vector of length 2 specifying an interval of real numbers.
This interval will be used instead of the range of pixel
values. The interval from \code{zlim[1]} to \code{zlim[2]} will be
mapped to the colours in \code{col}. This facility enables the user to
plot several images using a consistent colour map.
Alternatively if the argument \code{breaks} is given, then this specifies
the endpoints of the subintervals that are mapped to each colour.
This is incompatible with \code{zlim}.
The arguments \code{col} and \code{zlim} or \code{breaks}
are passed to the function \code{\link{image.default}}.
For examples of the use of these arguments,
see \code{\link{image.default}}.
}
}
Other graphical parameters controlling the display of both the pixel image
and the ribbon are passed through the \code{...} arguments
directly to the function \code{\link{image.default}}.
To suppress the axis tick marks and labels, set \code{axes=FALSE}.
}
\seealso{
\code{\link{im.object}},
\code{\link{colourmap}},
\code{\link{contour.im}},
\code{\link{persp.im}},
\code{\link{image.default}},
\code{\link{spatstat.options}}
}
\examples{
# an image
Z <- setcov(owin())
plot(Z)
# stretchable colour map
plot(Z, col=terrain.colors(128), axes=FALSE)
# fixed colour map
tc <- colourmap(rainbow(128), breaks=seq(-1,2,length=129))
plot(Z, col=tc)
}
\author{Adrian Baddeley
\email{adrian@maths.uwa.edu.au}
\url{http://www.maths.uwa.edu.au/~adrian/}
and Rolf Turner
\email{r.turner@auckland.ac.nz}
}
\keyword{spatial}
\keyword{hplot}