curveDepth (version 0.1.0.16)

images2curves: Convert images to curves

Description

Converts images to curves with points sorted in traversing order.

Usage

images2curves(images)

Value

A list of curves where each element is a function being a list containing a matrix coords (curve's values, d columns).

Arguments

images

A 3-dimensional array with each slice (matrix in first two dimensions) corresponding to an image. Each (eps-strictly) positive entry is regarded as an occupied pixel (one), otherwise it is regarded as an empty pixel, of an image.

References

Lafaye De Micheaux, P., Mozharovskyi, P. and Vimond, M. (2018). Depth for curve data and applications.

Examples

library(curveDepth)
# Pixel-grid filling function for an image
plotGridImage <- function(dims){
  redDims1 <- dims[1] - 1
  redDims2 <- dims[2] - 1
  for (i in 1:(dims[1] - 1)){
    lines(c(i / redDims1 - 0.5 / redDims1,
            i / redDims1 - 0.5 / redDims1),
            c(0 - 0.5 / redDims2, 1 + 0.5 / redDims2),
            lwd = 1, lty = 3, col = "lightgray")
    lines(c(0 - 0.5 / redDims1, 1 + 0.5 / redDims1),
          c(i / redDims2 - 0.5 / redDims2,
            i / redDims2 - 0.5 / redDims2),
            lwd = 1, lty = 3, col = "lightgray")
  }
  rect(0 - 0.5 / redDims1, 0 - 0.5 / redDims2,
       1 + 0.5 / redDims1, 1 + 0.5 / redDims2)
}
# Pixel-grid filling function for a curve
plotGridCurve <- function(dims){
  for (i in 1:(dims[1] - 1)){
    lines(c(i / dims[1], i / dims[1]), c(0, 1),
          lwd = 1, lty = 3, col = "lightgray")
    lines(c(0, 1), c(i / dims[2], i / dims[2]),
          lwd = 1, lty = 3, col = "lightgray")
  }
  rect(0, 0, 1, 1)
}
# Load a digit and plot it
data("mnistShort017")
  aSevenDigit <- mnistShort017$`7`[, , 5]
image(as.matrix(rev(as.data.frame(aSevenDigit))),
      col = gray((255:0) / 256), asp = 1,
      xlim = c(0 - 1 / 27, 1 + 1 / 27),
      ylim = c(0 - 1 / 27, 1 + 1 / 27))
plotGridImage(dim(aSevenDigit)[1:2])
# Convert the digit to a curve and plot it
aSevenCurve <- images2curves(array(
  aSevenDigit, dim = c(28, 28, 1)))[[1]]
plot(cbind(aSevenCurve$coords[, 1],
           1 - aSevenCurve$coords[, 2]),
           type = "l", lwd = 3, asp = 1,
           xlim = c(0, 1), ylim = c(0, 1),
           xlab = "x", ylab = "y")
  plotGridCurve(dim(aSevenDigit)[1:2])