

_D_i_s_p_l_a_y _a _c_o_l_o_r _i_m_a_g_e

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

_A_r_g_u_m_e_n_t_s:

     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.
          If the list has component `z' this is used for
          `z'.

       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 `rain-
          bow', `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.

_D_e_s_c_r_i_p_t_i_o_n:

     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.

_N_o_t_e:

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

_S_e_e _A_l_s_o:

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

_E_x_a_m_p_l_e_s:

     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)

