1 files changed, 160 insertions, 0 deletions
diff --git a/wipesides.go b/wipesides.go
new file mode 100644
index 0000000..8cd2060
--- /dev/null
+++ b/wipesides.go
@@ -0,0 +1,160 @@
+package preproc
+
+// TODO: add minimum size variable (default ~30%?)
+// TODO: switch to an interface rather than integralimg.I
+
+import (
+	"errors"
+	"fmt"
+	"image"
+	"image/color"
+	"image/draw"
+	_ "image/jpeg"
+	"image/png"
+	"os"
+
+	"rescribe.xyz/preproc/integralimg"
+)
+
+// returns the proportion of the given window that is black pixels
+func proportion(i integralimg.I, x int, size int) float64 {
+	w := i.GetVerticalWindow(x, size)
+	return w.Proportion()
+}
+
+// findbestedge goes through every vertical line from x to x+w to
+// find the one with the lowest proportion of black pixels.
+func findbestedge(img integralimg.I, 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(img, 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 near 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(img integralimg.I, wsize int, thresh float64) (int, int) {
+	maxx := len(img[0]) - 1
+	var lowedge, highedge int = 0, maxx
+
+	// don't start at the middle, as this will fail for 2 column layouts,
+	// start 10% left or right of the middle
+	notcentre := maxx / 10
+
+	for x := maxx/2 + notcentre; x < maxx-wsize; x++ {
+		if proportion(img, x, wsize) <= thresh {
+			highedge = findbestedge(img, x, wsize)
+			break
+		}
+	}
+
+	for x := maxx/2 - notcentre; x > 0; x-- {
+		if proportion(img, x, wsize) <= thresh {
+			lowedge = findbestedge(img, 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
+}
+
+// toonarrow checks whether the area between lowedge and highedge is
+// less than min % of the total image width
+func toonarrow(img *image.Gray, lowedge int, highedge int, min int) bool {
+	b := img.Bounds()
+	imgw := b.Max.X - b.Min.X
+	wipew := highedge - lowedge
+	if float64(wipew)/float64(imgw)*100 < float64(min) {
+		return true
+	}
+	return false
+}
+
+// Wipe fills the sections of image which fall outside the content
+// area with white, providing the content area is above min %
+func Wipe(img *image.Gray, wsize int, thresh float64, min int) *image.Gray {
+	integral := integralimg.ToIntegralImg(img)
+	lowedge, highedge := findedges(integral, wsize, thresh)
+	if toonarrow(img, lowedge, highedge, min) {
+		return img
+	}
+	return wipesides(img, lowedge, highedge)
+}
+
+// WipeFile wipes an image file, filling the sections of the image
+// which fall outside the content area with white, providing the
+// content area is above min %.
+// inPath: path of the input image.
+// outPath: path to save the output image.
+// wsize: window size for wipe algorithm.
+// thresh: threshold for wipe algorithm.
+// min: minimum % of content area width to consider valid.
+func WipeFile(inPath string, outPath string, wsize int, thresh float64, min int) error {
+	f, err := os.Open(inPath)
+	defer f.Close()
+	if err != nil {
+		return errors.New(fmt.Sprintf("Could not open file %s: %v", inPath, err))
+	}
+	img, _, err := image.Decode(f)
+	if err != nil {
+		return errors.New(fmt.Sprintf("Could not decode image: %v", err))
+	}
+	b := img.Bounds()
+	gray := image.NewGray(image.Rect(0, 0, b.Dx(), b.Dy()))
+	draw.Draw(gray, b, img, b.Min, draw.Src)
+
+	clean := Wipe(gray, wsize, thresh, min)
+
+	f, err = os.Create(outPath)
+	if err != nil {
+		return errors.New(fmt.Sprintf("Could not create file %s: %v", outPath, err))
+	}
+	defer f.Close()
+	err = png.Encode(f, clean)
+	if err != nil {
+		return errors.New(fmt.Sprintf("Could not encode image: %v", err))
+	}
+	return nil
+}