package o1.hofuncs

// This program is introduced in Chapter 5.5.

import o1._

object Task1 extends App {

  def toNaiveGray(color: Color) = {
    val luminance = (color.red + color.blue + color.green) / 3
    Color(luminance, luminance, luminance)
  }

  // The function toNaiveGray above takes in a color and returns a grayscale ("colorless")
  // version of it, that is, a shade of gray between white and black. As you can see from
  // the implementation, the R, G, and B components of a shade of gray are equal.
  //
  // toNaiveGray computes the shade of gray with a simple average: each of the three
  // components has an equal weight of 1/3. This works fairly okay, as you can tell by
  // running the program.
  //
  // However, the human eye is most sensitive to green light and much less sensitive to blue.
  // Therefore, to produce a grayscale image that humans perceive as equally luminous (bright)
  // as the original, we need to give different weights to the components of the original color:
  // the green component should have the greatest weight and the blue component the least.
  // Here is a common formula (see https://en.wikipedia.org/wiki/Grayscale):
  //   luminance = 0.2126*R + 0.7152*G + 0.0722*B
  // Such a grayscale filter that seeks to preserve perceived luminosity is called
  // "colorimetric".
  //
  // Your task is to modify this program by adding a function toColorimetricGray, which works
  // like toNaiveGray except that it uses the above formula to return a more realistic shade
  // of gray. Use the new function below (instead of toNaiveGray) to compute grayPic.
  //
  // Note: You can pass in Doubles as you construct a Color; they will be rounded to the
  // nearest Int.

  val originalPic = Pic("kid.png")
  val grayPic = originalPic.transformColors(toColorimetricGray)


  originalPic.leftOf(grayPic).show()

  def toColorimetricGray(color: Color) = {

    val luminance = ((color.red) * 0.2126 + (color.blue * 0.0722) + (color.green * 0.7152))
    Color(luminance, luminance, luminance)
  }

}