1 files changed, 116 insertions, 0 deletions
diff --git a/binarize/integralimg.go b/binarize/integralimg.go
new file mode 100644
index 0000000..c585d60
--- /dev/null
+++ b/binarize/integralimg.go
@@ -0,0 +1,116 @@
+package main
+
+import (
+	"image"
+	"math"
+)
+
+type integralwindow struct {
+	topleft uint64
+	topright uint64
+	bottomleft uint64
+	bottomright uint64
+	width int
+	height int
+}
+
+func integralimg(img *image.Gray) [][]uint64 {
+	b := img.Bounds()
+	var oldy, oldx, oldxy uint64
+	var integral [][]uint64
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		newrow := []uint64{}
+		for x := b.Min.X; x < b.Max.X; x++ {
+			oldx, oldy, oldxy = 0, 0, 0
+			if x > 0 {
+				oldx = newrow[x-1]
+			}
+			if y > 0 {
+				oldy = integral[y-1][x]
+			}
+			if x > 0 && y > 0 {
+				oldxy = integral[y-1][x-1]
+			}
+			pixel := uint64(img.GrayAt(x, y).Y)
+			i := pixel + oldx + oldy - oldxy
+			newrow = append(newrow, i)
+		}
+		integral = append(integral, newrow)
+	}
+	return integral
+}
+
+func integralimgsq(img *image.Gray) [][]uint64 {
+	b := img.Bounds()
+	var oldy, oldx, oldxy uint64
+	var integral [][]uint64
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		newrow := []uint64{}
+		for x := b.Min.X; x < b.Max.X; x++ {
+			oldx, oldy, oldxy = 0, 0, 0
+			if x > 0 {
+				oldx = newrow[x-1]
+			}
+			if y > 0 {
+				oldy = integral[y-1][x]
+			}
+			if x > 0 && y > 0 {
+				oldxy = integral[y-1][x-1]
+			}
+			pixel := uint64(img.GrayAt(x, y).Y)
+			i := pixel * pixel + oldx + oldy - oldxy
+			newrow = append(newrow, i)
+		}
+		integral = append(integral, newrow)
+	}
+	return integral
+}
+
+// this gets the values of the four corners of a window, which can
+// be used to quickly calculate the mean of the area
+func getintegralwindow(integral [][]uint64, x int, y int, size int) integralwindow {
+	step := size / 2
+
+	minx, miny := 0, 0
+	maxy := len(integral)-1
+	maxx := len(integral[0])-1
+
+	if y > (step+1) {
+		miny = y - step - 1
+	}
+	if x > (step+1) {
+		minx = x - step - 1
+	}
+
+	if maxy > (y + step) {
+		maxy = y + step
+	}
+	if maxx > (x + step) {
+		maxx = x + step
+	}
+
+	return integralwindow { integral[miny][minx], integral[miny][maxx], integral[maxy][minx], integral[maxy][maxx], maxx-minx, maxy-miny}
+}
+
+func integralmean(integral [][]uint64, x int, y int, size int) float64 {
+	i := getintegralwindow(integral, x, y, size)
+	total := float64(i.bottomright + i.topleft - i.topright - i.bottomleft)
+	sqsize := float64(i.width) * float64(i.height)
+	return total / sqsize
+}
+
+func integralmeanstddev(integral [][]uint64, integralsq [][]uint64, x int, y int, size int) (float64, float64) {
+	i := getintegralwindow(integral, x, y, size)
+	isq := getintegralwindow(integralsq, x, y, size)
+
+	var total, sqtotal, sqsize float64
+
+	sqsize = float64(i.width) * float64(i.height)
+
+	total = float64(i.bottomright + i.topleft - i.topright - i.bottomleft)
+	sqtotal = float64(isq.bottomright + isq.topleft - isq.topright - isq.bottomleft)
+
+	mean := total / sqsize
+	variance := (sqtotal / sqsize) - (mean * mean)
+	return mean, math.Sqrt(variance)
+}