Read a PNG as a grayscale single-channel image. Converts from RGB to G (single channel color array of bytes 0-255).

image-grayscale.png

readPNG.R

library('png')

# Load a png image as a grayscale single-channel byte array (0-255).
loadImage <- function(filename) {
  data <- readPNG(filename)

  result <- c()
  
  # Convert to single-channel grayscale RGBA -> G, using the average method.
  for (i in 1:nrow(data)) {
    for (j in 1:ncol(data)) {
      rgba <- data[i,j,] # Row i column j
      g <- round(256 * mean(rgba[1:3]) / 3)
      
      result <- c(g, result)
    }
  }
  
  list(bytes=result, nrow=nrow(data), ncol=ncol(data))
}

d <- loadImage('shirt2-28x28.png')
dd <- matrix(d$bytes, d$nrow, d$ncol)
image(dd, col=gray(seq(0, 1, length=256)))

readPNG2.R

# This version is compatible with the readMNIST.R example. The only difference is the orientation of the resulting byte array.
# c(result, g) versus c(g, result)

library('png')

show_digit <- function(arr784, col=gray(12:1/12), ...) {
  image(matrix(arr784, nrow=28)[,28:1], col=col, ...)
}

# Load a png image as a grayscale single-channel byte array (0-255).
loadImage <- function(filename) {
  data <- readPNG(filename)

  result <- c()
  
  # Convert to single-channel grayscale RGBA -> G, using the average method.
  for (i in 1:nrow(data)) {
    for (j in 1:ncol(data)) {
      rgba <- data[i,j,] # Row i column j
      g <- round(256 * mean(rgba[1:3]) / 3)
      
      result <- c(result, g)
    }
  }
  
  list(bytes=result, nrow=nrow(data), ncol=ncol(data))
}

d <- loadImage('shirt3-28x28.png')
show_digit(d$bytes)