demo/JSSdemo1.R

### Demo presenting the code to replicate the first example from the
### 2017 JSS publication on the kohonen package v. 3.0, the image
### segmentation of the pepper plant. Training the SOM for the pepper
### image takes some time, on my laptop approx 40 seconds.

require("kohonen")
require("RColorBrewer")

## function to plot the pepper picture
plot.picture <- function(dmat, what = c("col", "truth"),
                         image.dims = c(600, 800), mycols, ...) {
  what <- match.arg(what)

  if (what == "truth") { # dmat is a factor
    require(lattice)    
    if (missing(mycols)) {
      mycols <- brewer.pal(nlevels(dmat), "Set1")
    }
    myat <- 0:nlevels(dmat) + .5
    immat <- matrix(as.numeric(dmat), image.dims[1], image.dims[2])
    print(levelplot(t(immat)[,nrow(immat):1], at = myat,
                    colorkey = list(at = myat,
                                    space = "top",
                                    col = mycols,
                                    labels = list(at = myat[-1] - .5,
                                                  labels = levels(dmat))),
                    col.regions = mycols, xlab = "", ylab = "", ...))
   } else { # dmat is a matrix with columns "red", "green" and "blue"
    require("grid")
    immat <- rgb(dmat[,"red"], dmat[,"green"], dmat[,"blue"],
                 maxColorValue = 255)
    dim(immat) <- image.dims
    grid.raster(immat, interpolate = FALSE, ...)
  }
}

### ####################################################################
### Image segmentation example

## Prepare input data
data(peppaPic)
X <- peppaPic[,c("red", "green", "blue")]
Y <- factor(peppaPic[,"truth"])
classes <- c("background", "leaves", "peppers", "peduncles", "stems",
             "sideshoots", "wires", "cuts")
levels(Y) <- classes
coords <- cbind(rep(1:800, each = 600), rep(1:600, 800))
colnames(coords) <- c("x", "y")

imdata <- list("rgb" = X, "truth" = Y, "coords" = coords)

## do segmentation
mygrid <- somgrid(4, 8, "hexagonal")
set.seed(15)
system.time(somsegm1 <- supersom(imdata, whatmap = c("rgb", "coords"),
                                 user.weights = c(1, 9),
                                 grid = mygrid))
## reconstruct the original image
reconstrIm <- predict(somsegm1, newdata = imdata)
X32 <- reconstrIm$predictions[["rgb"]]

plot.picture(X, x = unit(.025, "npc"),
             just = "left", width = unit(.45, "npc"))
plot.picture(X32, x = unit(.525, "npc"), 
             just = "left", width = unit(.45, "npc"))

## find class predictions for map units, concentrate only on peppers
## and leaves
truthpredictions <-
  classmat2classvec(reconstrIm$unit.predictions$truth)
trclasses <- levels(truthpredictions)
trclasses[!(trclasses %in% c("leaves", "peppers"))] <- "other"
levels(truthpredictions) <- trclasses
pepperunits <- which(truthpredictions == "peppers")

## visualize the rgb part of the map, using unit class labels as
## background colors
rgbpalette <- function(n) {
  if (n != 3) stop("Hey! Count again!")
  c("red", "green", "blue")
}
cluscolors <- brewer.pal(nlevels(truthpredictions), "Set3")
unitcols <- cluscolors[as.integer(truthpredictions)]
plot(somsegm1, "codes", whatmap = "rgb", bgcol = unitcols, 
     palette.name = rgbpalette, main = "")
## add unit numbers and a legend on top
idx <- (0:7)*4 + 1
text(somsegm1$grid$pts[idx,1] - .5, somsegm1$grid$pts[idx,2], 
     labels = idx, pos = 2)
add.cluster.boundaries(somsegm1, truthpredictions)
legend("top", legend = rev(levels(truthpredictions)), bty="n",
       pch = rep(21, 3), pt.bg = rev(cluscolors), ncol = 3)

## visualize the pixel location part of the map
dev.new()
plot(somsegm1$codes[["coords"]][,1], 
     max(somsegm1$codes[["coords"]][,2]) - somsegm1$codes[["coords"]][,2],
     pch = 21, cex = 3, axes = FALSE, xlab = "", ylab = "",
     bg = rgb(somsegm1$codes[["rgb"]][,1],
                          somsegm1$codes[["rgb"]][,2],
                          somsegm1$codes[["rgb"]][,3], maxColorValue = 255))
## numbers of pepper units are printed in red
text(somsegm1$codes[["coords"]][,1],
     max(somsegm1$codes[["coords"]][,2]) - 
     somsegm1$codes[["coords"]][,2],
     col = (1:nrow(somsegm1$codes[["coords"]]) %in% pepperunits) + 1,
     labels = 1:nrow(somsegm1$codes[["coords"]]), pos = 1, offset = .8)
box()

## visualize the pixels that are projected to the pepper units
dev.new()
oneclass <- rep("background", 480000)
for (ii in seq(along = pepperunits))
  oneclass[reconstrIm$unit.classif == pepperunits[ii]] <-
    paste("unit", pepperunits[ii])
oneclass <- factor(oneclass)
nregions <- nlevels(oneclass)
classcols <- c("lightgray", brewer.pal(max(3, nregions), "Set1"))
plot.picture(oneclass, what = "truth",
             mycols = classcols[1:(nregions + 1)],
             scales = list(draw = FALSE))

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kohonen documentation built on Aug. 29, 2017, 1:07 a.m.