Adding a color legend to an image

Question

I have a matrix that I made an image of using image(matrix). Is there away to add a legend of the colors to my image like I do when adding a legend to plot?

Answer 1

Or the legend could be provided like this:

     legend(grconvertX(0.5, "device"), grconvertY(1, "device"), 
     c("0",".5","1"), fill = colMap[c(1, 10, 20)], xpd = NA)

where grconvertX() and grconvertY() and xpd makes sure the legend is outside the plotting region. A plausible example would be:

    nsamples <- 20
    mat <- rnorm(nsamples, .5, .15)
    dim(mat) <- c(4, 5)
    colMap <- colorRampPalette(c("red","white","blue" ))(nsamples)
    image(1:4, 1:5, mat, col = colMap, ylab="", xlab="")
    legend(grconvertX(0.5, "device"), grconvertY(1, "device"),
    c("0",".5","1"), fill = colMap[c(1, 10, 20)], xpd = NA)

p.s.: I know it is an old request and it is solved. However I was looking for a similar answer and I could not find it. Since I bother solving this issue I thought maybe someone else could also benefit from it.

Answer 2

image in R is a fairly basic plotting function. You might want to look at filled.contour if you want a function that will automatically allocate space for a legend. Or try this:

 library(lattice)
 levelplot(matrix)