Adjust color scale of image plot in R

Question

The image.plot function automatically generate the color scale for the inputs. For example,

library(fields)
x <- 1:10
y <- 1:15
z <- outer(x, y, "+")
image.plot(x, y, z)

will generate a figure like this Now I want to adjust the color scale to the range from 0 to 20, and any values above 20 need to be colored the same as 20. So I added zlim=c(0,20) in the function parameters, and I get, The problem is, although zlim adjusted the color scale range, the values above the limit were not assigned a color. How can I fix this? In this case, I want the up-right corner to be colored dark red i.e. to have the color assigned from the end of the color range.

Answer 1

You could use z[z > 20] <- 20 to achieve that with image.plot.

library(fields)
x <- 1:10
y <- 1:15
z <- outer(x, y, "+")
z[z > 20] <- 20
image.plot(x, y, z)