June 2018 Update

Task/Bitmap-Histogram/Kotlin/bitmap-histogram.kotlin

@@ -0,0 +1,61 @@
+// version 1.2.10
+
+import java.io.File
+import java.awt.image.BufferedImage
+import javax.imageio.ImageIO
+
+const val BLACK = 0xff000000.toInt()
+const val WHITE = 0xffffffff.toInt()
+
+fun luminance(argb: Int): Int {
+    val red   = (argb shr 16) and 0xFF
+    val green = (argb shr  8) and 0xFF
+    val blue  =  argb and 0xFF
+    return (0.2126 * red + 0.7152 * green + 0.0722 * blue).toInt()
+}
+
+val BufferedImage.histogram: IntArray
+    get() {
+        val lumCount = IntArray(256)
+        for (x in 0 until width) {
+            for (y in 0 until height) {
+                var argb = getRGB(x, y)
+                lumCount[luminance(argb)]++
+            }
+        }
+        return lumCount
+    }
+
+fun findMedian(histogram: IntArray): Int {
+    var lSum  = 0
+    var rSum  = 0
+    var left  = 0
+    var right = 255
+    do {
+        if (lSum < rSum) lSum += histogram[left++]
+        else             rSum += histogram[right--]
+    }
+    while (left != right)
+    return left
+}
+
+fun BufferedImage.toBlackAndWhite(median: Int) {
+    for (x in 0 until width) {
+        for (y in 0 until height) {
+            val argb = getRGB(x, y)
+            val lum  = luminance(argb)
+            if (lum < median)
+                setRGB(x, y, BLACK)
+            else
+                setRGB(x, y, WHITE)
+        }
+    }
+}
+
+fun main(args: Array<String>) {
+    val image = ImageIO.read(File("Lenna100.jpg"))
+    val median = findMedian(image.histogram)
+    image.toBlackAndWhite(median)
+    val bwFile = File("Lenna_bw.jpg")
+    ImageIO.write(image, "jpg", bwFile)
+}