Generates a color histogram of an image to compute image distance Raw

Histogram.scala

import java.awt.image.BufferedImage
import java.io.File
import javax.imageio.ImageIO

case class Histogram(
  resolution: Int,
  pixels: Int,
  histogram: Array[Array[Array[Int]]]
) {
  def distance(that: Histogram): Double = {
    require(this.resolution == that.resolution)
    var sumOfSquares: Double = 0.
    for (r <- 0 until resolution; g <- 0 until resolution; b <- 0 until resolution) {
      val diff: Double =
        this.histogram(r)(g)(b).toDouble / this.pixels - that.histogram(r)(g)(b).toDouble / that.pixels
      sumOfSquares += (diff * diff)
    }
    return Math.sqrt(sumOfSquares)
  }

  override def toString(): String = {
    val histogramString: String = histogram.map(_.map(_.toList).toList).toList.toString
    return s"Histogram($resolution,$pixels,$histogramString)"
  }
}

object Histogram {
  val BYTE: Int = 256

  def apply(file: String, resolution: Int): Histogram = {
    apply(ImageIO.read(new File(file)), resolution)
  }

  def apply(image: BufferedImage, resolution: Int): Histogram = {
    val bucketSize: Int = BYTE / resolution
    val numPixels: Int = image.getHeight * image.getWidth
    val pixels: Array[Int] = image.getRGB(
      0,
      0,
      image.getWidth,
      image.getHeight,
      null,
      0,
      image.getWidth
    )
    val histogram: Array[Array[Array[Int]]] = Array.ofDim[Int](resolution, resolution, resolution)
    for (i: Int <- pixels) {
      val (_, r: Int, g: Int, b: Int) = pixel(i)
      histogram(
        Math.min(resolution - 1, r / bucketSize)
      )(
        Math.min(resolution - 1, g / bucketSize)
      )(
        Math.min(resolution - 1, b / bucketSize)
      ) += 1
    }
    return Histogram(resolution, numPixels, histogram)
  }

  def pixel(pixel: Int): (Int, Int, Int, Int) = {
    return (
      (pixel >> 24) & 0xff,
      (pixel >> 16) & 0xff,
      (pixel >> 8) & 0xff,
      pixel & 0xff
    )
  }
}