| image {graphics} | R Documentation |
Creates a grid of colored or gray-scale rectangles with colors
corresponding to the values in z. This can be used to display
three-dimensional or spatial data aka “images”.
This is a generic function.
The functions heat.colors, terrain.colors
and topo.colors create heat-spectrum (red to white) and
topographical color schemes suitable for displaying ordered data, with
n giving the number of colors desired.
image(x, ...)
## Default S3 method:
image(x, y, z, zlim, xlim, ylim, col = heat.colors(12),
add = FALSE, xaxs = "i", yaxs = "i", xlab, ylab,
breaks, oldstyle = FALSE, ...)
x,y |
locations of grid lines at which the values in z are
measured. These must be finite, non-missing and in (strictly)
ascending order. By default, equally
spaced values from 0 to 1 are used. If x is a list,
its components x$x and x$y are used for x
and y, respectively. If the list has component z this
is used for z. |
z |
a matrix containing the values to be plotted (NAs are
allowed). Note that x can be used instead of z for
convenience. |
zlim |
the minimum and maximum z values for which colors
should be plotted, defaulting to the range of the finite values of
z. Each of the given colors will be used to color an
equispaced interval of this range. The midpoints of the
intervals cover the range, so that values just outside the range
will be plotted. |
xlim, ylim |
ranges for the plotted x and y values,
defaulting to the range of the finite values of x and y. |
col |
a list of colors such as that generated by
rainbow, heat.colors,
topo.colors, terrain.colors or similar
functions. |
add |
logical; if TRUE, add to current plot (and disregard
the following arguments). This is rarely useful because
image “paints” over existing graphics. |
xaxs, yaxs |
style of x and y axis. The default "i" is
appropriate for images. See par. |
xlab, ylab |
each a character string giving the labels for the x and
y axis. Default to the ‘call names’ of x or y, or to
"" if these where unspecified. |
breaks |
a set of breakpoints for the colours: must give one more breakpoint than colour. |
oldstyle |
logical. If true the midpoints of the colour intervals
are equally spaced, and zlim[1] and zlim[2] were taken
to be midpoints. (This was the default prior to R 1.1.0.)
The current default is to have colour intervals of equal lengths
between the limits. |
... |
graphical parameters for plot may also be
passed as arguments to this function, as can the plot aspect ratio
asp (see plot.window). |
The length of x should be equal to the nrow(z)+1 or
nrow(z). In the first case x specifies the boundaries
between the cells: in the second case x specifies the midpoints
of the cells. Similar reasoning applies to y. It probably
only makes sense to specify the midpoints of an equally-spaced
grid. If you specify just one row or column and a length-one x
or y, the whole user area in the corresponding direction is
filled.
Rectangles corresponding to missing values are not plotted (and so are
transparent and (unless add=TRUE) the default background painted
in par("bg") will show though and if that is transparent, the
canvas colour will be seen).
If breaks is specified then zlim is unused and the
algorithm used follows cut, so intervals are closed on
the right and open on the left except for the lowest interval.
Notice that image interprets the z matrix as a table of
f(x[i], y[j]) values, so that the x axis corresponds to row
number and the y axis to column number, with column 1 at the bottom,
i.e. a 90 degree counter-clockwise rotation of the conventional
printed layout of a matrix.
Based on a function by Thomas Lumley tlumley@u.washington.edu.
filled.contour or heatmap which can
look nicer (but are less modular),
contour;
heat.colors, topo.colors,
terrain.colors, rainbow,
hsv, par.
x <- y <- seq(-4*pi, 4*pi, len=27)
r <- sqrt(outer(x^2, y^2, "+"))
image(z = z <- cos(r^2)*exp(-r/6), col=gray((0:32)/32))
image(z, axes = FALSE, main = "Math can be beautiful ...",
xlab = expression(cos(r^2) * e^{-r/6}))
contour(z, add = TRUE, drawlabels = FALSE)
# Volcano data visualized as matrix. Need to transpose and flip
# matrix horizontally.
image(t(volcano)[ncol(volcano):1,])
# A prettier display of the volcano
x <- 10*(1:nrow(volcano))
y <- 10*(1:ncol(volcano))
image(x, y, volcano, col = terrain.colors(100), axes = FALSE)
contour(x, y, volcano, levels = seq(90, 200, by = 5),
add = TRUE, col = "peru")
axis(1, at = seq(100, 800, by = 100))
axis(2, at = seq(100, 600, by = 100))
box()
title(main = "Maunga Whau Volcano", font.main = 4)