tristanwietsma · October 1, 2014 03:58 · Oct 1, 2014
diff --git a/hist.go b/hist.go
@@ -0,0 +1,49 @@
+package main
+
+import (
+        "flag"
+        "fmt"
+        "image"
+        _ "image/gif"
+        _ "image/jpeg"
+        _ "image/png"
+        "log"
+        "os"
+)
+
+var infile = flag.String("infile", "img.png", "path to image (gif, jpeg, png)")
+
+func main() {
+
+        flag.Parse()
+        reader, err := os.Open(*infile)
+        if err != nil {
+                log.Fatal(err)
+        }
+        defer reader.Close()
+
+        m, _, err := image.Decode(reader)
+        if err != nil {
+                log.Fatal(err)
+        }
+        bounds := m.Bounds()
+
+        var histogram [16][4]int
+        for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+                for x := bounds.Min.X; x < bounds.Max.X; x++ {
+                        r, g, b, a := m.At(x, y).RGBA()
+                        // A color's RGBA method returns values in the range [0, 65535].
+                        // Shifting by 12 reduces this to the range [0, 15].
+                        histogram[r>>12][0]++
+                        histogram[g>>12][1]++
+                        histogram[b>>12][2]++
+                        histogram[a>>12][3]++
+                }
+        }
+
+        // Print the results.
+        fmt.Printf("%-14s %6s %6s %6s %6s\n", "bin", "red", "green", "blue", "alpha")
+        for i, x := range histogram {
+                fmt.Printf("0x%04x-0x%04x: %6d %6d %6d %6d\n", i<<12, (i+1)<<12-1, x[0], x[1], x[2], x[3])
+        }
+}