http://ice1000.org/2017/04/20/ImageToText/

Image2Ascii.kt

import java.awt.Color
import java.awt.image.BufferedImage
import java.net.URL
import javax.imageio.ImageIO

object Image2Ascii {
    private fun colorAverage(image: BufferedImage, x: Int, y: Int): Color {
        val sampleDiff = step - 1

        val lt = Color(image.getRGB(x, y + sampleDiff))
        val rt = Color(image.getRGB(x + sampleDiff, y + sampleDiff))
        val ld = Color(image.getRGB(x, y))
        val rd = Color(image.getRGB(x + sampleDiff, y))

        return Color(average(lt.red, rt.red, ld.red, rd.red),
                average(lt.green, rt.green, ld.green, rd.green),
                average(lt.blue, rt.blue, ld.blue, rd.blue))
    }

    private fun average(vararg args: Int): Int {
        val sum = args.reduce { acc, i -> acc + i }
        return sum / args.size
    }

    private fun image(args: Array<out String>): BufferedImage? = ImageIO.read(URL(args.firstOrNull()))

    private fun printAscii(r: Int, g: Int, b: Int) = print(if (average(r, g, b) <= boundary) white else black)

    private const val black = '■'
    private const val white = '□'

    private const val boundary: Int = 0x7f
    private const val step: Int = 1

    @JvmStatic
    fun main(vararg args: String) {
        val img = image(args)!!

        println(img)

        for (y in 0 until img.height step step) {
            for (x in 0 until img.width step step) {
                val ca = colorAverage(img, x, y)
                printAscii(ca.red, ca.green, ca.blue)
            }
            println()
        }

        println("black $black white $white boundary $boundary step $step")
    }
}