FavIcon Cake - maps from a png to another png with a smaller palette (and counts how many pixels there are of each colour)

favicon-cake.scala

/*
This scala script takes in a small png file and converts it to a grayscale image with a smaller
palette size; counting the number of each pixels in the original and resulting image.
 */
import java.awt.image.BufferedImage
import java.io.File
import javax.imageio.ImageIO
import scala.collection.JavaConversions._
import scala.math.floor

object Pixel {
  def luminance(lum: Int):Pixel = new Pixel((lum << 16) + (lum << 8) + lum)
}

case class Pixel(rgb: Int) extends Ordered[Pixel] {
  val red: Int = (rgb >> 16) & 0xff
  val green: Int = (rgb >> 8) & 0xff
  val blue: Int = rgb & 0xff
  val luminance: Int = floor((.3 * red) + (.59 * green) + (.11 * blue)).toInt
  override def toString = "RGBL(%d,%d,%d,%d)".format(red, green, blue, luminance)
  def compare(that: Pixel): Int = this.luminance.compare(that.luminance)
}

val paletteSize = 4
val faviconFileName = "/Users/shildrew/working/guardian-logo/src/favicon-blue.png"

val faviconURL = new File(faviconFileName)
val favicon = ImageIO.read(faviconURL)

val width = favicon.getWidth
val height = favicon.getHeight

val inputPixels = for ( x <- 0 until width;
                      y <- 0 until height )
    yield { Pixel(favicon.getRGB(x, y)) }

val sortedPixels = inputPixels.distinct.sorted

// this "- 20" makes the distribution better for me - similar to levels in photoshop
val darkest = sortedPixels.head.luminance - 20
val lightest = sortedPixels.last.luminance
val range = darkest to lightest by ((lightest - darkest) / (paletteSize - 1))

val colourPalette = range.map{ Pixel.luminance(_) }

val remappedPixels = inputPixels.map { pixel =>
  colourPalette.reduceLeft { (result, elem) =>
    if (result.compare(pixel) < elem.compare(pixel)) {
      result
    } else {
      elem
    }
  }
}

println("Distribution of remapped pixels (palette of "+paletteSize+"):")
println(remappedPixels.distinct.sorted.map{ pixel =>
  "Luminance: %4s   Count: %4s" format (pixel.luminance, remappedPixels.count( _ == pixel))
}.mkString("\n"))

val outputImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

for ( x <- 0 until width;
      y <- 0 until height) {
    val pixel = remappedPixels.get(x*16 + y)
    outputImage.setRGB(x,y,pixel.rgb)
}

val file = new File("output-new.png")
ImageIO.write(outputImage, "png", file);
println
println("Wrote to "+file.getAbsolutePath)

// Cake.write(outputImage)