code snippet from The Art of R Programming: A Tour of Statistical Software Design

mtrush.R

# a code snippet from the book: 
# The Art of R Programming: A Tour of Statistical Software Design

# load library
library("pixmap")

# show mtrush
mtrush1 = read.pnm("path/to/mtrush1.pgm")
mtrush1
plot(mtrush1)

# blot out a specific area
mtrush2 = mtrush1
mtrush2@grey[84:163, 135:177] = 1
plot(mtrush2)

# add noise
blurpart = function(img, rows, cols, q) {
  lrows = length(rows)
  lcols = length(cols)
  newimg = img
  randomnoise = matrix(nrow=lrows, ncol=lcols, runif(lrows * lcols))
  newimg@grey[rows, cols] = (1 - q) * img@grey[rows, cols] + q * randomnoise
  return(newimg)
}

blurpart(mtrush1, 84:163, 135:177, 0.65)
mtrush3 = blurpart(mtrush2, 84:163, 135:177, 0.65)
plot(mtrush3)