## Display a color image

## Usage

    image(x, y, z, zlim, col = heat.colors(12),
          add = FALSE, xaxs = "i", yaxs = "i", xlab, ylab, ...)

## Arguments

`x,y` | locations of grid lines at which the values in `z` are measured. These must be in 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.
`z` | a matrix containing the values to be plotted (`NA`s are allowed). Note that `x` can be used instead of `z` for convenience.
`zlim` | the minimum and maximum `z` values for which colors will be plotted. Each of the given colors will be used to color an equispaced interval of this range.
`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.
`...` | graphical parameters for `plot` may also be passed as arguments to this function.

## Description

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''. 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.

## Note

Based on a function by Thomas Lumley thomas@biostat.washington.edu.

## See Also

`contour`, `heat.colors`, `topo.colors`, `terrain.colors`, `rainbow`, `hsv`, `par`.

## Examples

    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=F, main="Math can be beautiful ...",
          xlab=expression(cos(r^2) * e^{-r/6}))
    contour(z, add=T)

    data(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)

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