1 files changed, 122 insertions, 0 deletions
diff --git a/preproc/wipesides.go b/preproc/wipesides.go
new file mode 100644
index 0000000..2afe1d2
--- /dev/null
+++ b/preproc/wipesides.go
@@ -0,0 +1,122 @@
+package preproc
+
+// TODO: add minimum size variable (default ~30%?)
+// TODO: have the integral image specific stuff done by interface functions
+
+import (
+	"image"
+	"image/color"
+)
+
+type windowslice struct {
+	topleft     uint64
+	topright    uint64
+	bottomleft  uint64
+	bottomright uint64
+}
+
+func getwindowslice(i [][]uint64, x int, size int) windowslice {
+	maxy := len(i) - 1
+	maxx := x + size
+	if maxx > len(i[0])-1 {
+		maxx = len(i[0]) - 1
+	}
+
+	return windowslice{i[0][x], i[0][maxx], i[maxy][x], i[maxy][maxx]}
+}
+
+// checkwindow checks the window from x to see whether more than
+// thresh proportion of the pixels are white, if so it returns true.
+func checkwindow(integral [][]uint64, x int, size int, thresh float64) bool {
+	height := len(integral)
+	window := getwindowslice(integral, x, size)
+	// divide by 255 as each on pixel has the value of 255
+	sum := (window.bottomright + window.topleft - window.topright - window.bottomleft) / 255
+	area := size * height
+	proportion := float64(area)/float64(sum) - 1
+	return proportion <= thresh
+}
+
+// returns the proportion of the given window that is black pixels
+func proportion(integral [][]uint64, x int, size int) float64 {
+	height := len(integral)
+	window := getwindowslice(integral, x, size)
+	// divide by 255 as each on pixel has the value of 255
+	sum := (window.bottomright + window.topleft - window.topright - window.bottomleft) / 255
+	area := size * height
+	return float64(area)/float64(sum) - 1
+}
+
+// findbestedge goes through every vertical line from x to x+w to
+// find the one with the lowest proportion of black pixels.
+func findbestedge(integral [][]uint64, x int, w int) int {
+	var bestx int
+	var best float64
+
+	if w == 1 {
+		return x
+	}
+
+	right := x + w
+	for ; x < right; x++ {
+		prop := proportion(integral, x, 1)
+		if prop > best {
+			best = prop
+			bestx = x
+		}
+	}
+
+	return bestx
+}
+
+// Findedges finds the edges of the main content, by moving a window of wsize
+// from the middle of the image to the left and right, stopping when it reaches
+// a point at which there is a lower proportion of black pixels than thresh.
+func Findedges(integral [][]uint64, wsize int, thresh float64) (int, int) {
+	maxx := len(integral[0]) - 1
+	var lowedge, highedge int = 0, maxx
+
+	for x := maxx / 2; x < maxx-wsize; x++ {
+		if checkwindow(integral, x, wsize, thresh) {
+			highedge = findbestedge(integral, x, wsize)
+			break
+		}
+	}
+
+	for x := maxx / 2; x > 0; x-- {
+		if checkwindow(integral, x, wsize, thresh) {
+			lowedge = findbestedge(integral, x, wsize)
+			break
+		}
+	}
+
+	return lowedge, highedge
+}
+
+// Wipesides fills the sections of image not within the boundaries
+// of lowedge and highedge with white
+func Wipesides(img *image.Gray, lowedge int, highedge int) *image.Gray {
+	b := img.Bounds()
+	new := image.NewGray(b)
+
+	// set left edge white
+	for x := b.Min.X; x < lowedge; x++ {
+		for y := b.Min.Y; y < b.Max.Y; y++ {
+			new.SetGray(x, y, color.Gray{255})
+		}
+	}
+	// copy middle
+	for x := lowedge; x < highedge; x++ {
+		for y := b.Min.Y; y < b.Max.Y; y++ {
+			new.SetGray(x, y, img.GrayAt(x, y))
+		}
+	}
+	// set right edge white
+	for x := highedge; x < b.Max.X; x++ {
+		for y := b.Min.Y; y < b.Max.Y; y++ {
+			new.SetGray(x, y, color.Gray{255})
+		}
+	}
+
+	return new
+}