Data commit

Task/Bitmap-Histogram/Go/bitmap-histogram-1.go

@@ -0,0 +1,24 @@
+package raster
+
+import "math"
+
+func (g *Grmap) Histogram(bins int) []int {
+    if bins <= 0 {
+        bins = g.cols
+    }
+    h := make([]int, bins)
+    for _, p := range g.px {
+        h[int(p)*(bins-1)/math.MaxUint16]++
+    }
+    return h
+}
+
+func (g *Grmap) Threshold(t uint16) {
+    for i, p := range g.px {
+        if p < t {
+            g.px[i] = 0
+        } else {
+            g.px[i] = math.MaxUint16
+        }
+    }
+}

Task/Bitmap-Histogram/Go/bitmap-histogram-2.go

@@ -0,0 +1,45 @@
+package main
+
+// Files required to build supporting package raster are found in:
+// * This task (immediately above)
+// * Bitmap
+// * Grayscale image
+// * Read a PPM file
+// * Write a PPM file
+
+import (
+    "raster"
+    "fmt"
+    "math"
+)
+
+func main() {
+    // (A file with this name is output by the Go solution to the task
+    // "Bitmap/Read an image through a pipe," but of course any 8-bit
+    // P6 PPM file should work.)
+    b, err := raster.ReadPpmFile("pipein.ppm")
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    g := b.Grmap()
+    h := g.Histogram(0)
+    // compute median
+    lb, ub := 0, len(h)-1
+    var lSum, uSum int
+    for lb <= ub {
+        if lSum+h[lb] < uSum+h[ub] {
+            lSum += h[lb]
+            lb++
+        } else {
+            uSum += h[ub]
+            ub--
+        }
+    }
+    // apply threshold and write output file
+    g.Threshold(uint16(ub * math.MaxUint16 / len(h)))
+    err = g.Bitmap().WritePpmFile("threshold.ppm")
+    if err != nil {
+        fmt.Println(err)
+    }
+}