Add zeroinv option for binarize command

3 files changed, 32 insertions, 3 deletions

diff --git a/binarize/cmd/binarize/main.go b/binarize/cmd/binarize/main.go
index c4b9562..bda3d93 100644
--- a/binarize/cmd/binarize/main.go
+++ b/binarize/cmd/binarize/main.go
@@ -20,11 +20,12 @@ func autowsize(bounds image.Rectangle) int {
 
 func main() {
 	flag.Usage = func() {
-		fmt.Fprintf(os.Stderr, "Usage: sauvola [-w num] [-k num] inimg outimg\n")
+		fmt.Fprintf(os.Stderr, "Usage: binarize [-k num] [-t type] [-w num] inimg outimg\n")
 		flag.PrintDefaults()
 	}
 	wsize := flag.Int("w", 0, "Window size for sauvola algorithm. Set automatically based on resolution if not set.")
 	ksize := flag.Float64("k", 0.5, "K for sauvola algorithm. This controls the overall threshold level. Set it lower for very light text (try 0.1 or 0.2).")
+	btype := flag.String("t", "binary", "Type of threshold. binary or zeroinv are currently implemented.")
 	flag.Parse()
 	if flag.NArg() < 2 {
 		flag.Usage()
@@ -55,7 +56,15 @@ func main() {
 
 	// TODO: come up with a way to set a good ksize automatically
 
-	thresh := binarize.IntegralSauvola(gray, *ksize, *wsize)
+	var thresh image.Image
+	thresh = binarize.IntegralSauvola(gray, *ksize, *wsize)
+
+	if *btype == "zeroinv" {
+		thresh, err = binarize.BinToZeroInv(thresh.(*image.Gray), img.(*image.RGBA))
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
 
 	f, err = os.Create(flag.Arg(1))
 	if err != nil {
diff --git a/binarize/sauvola.go b/binarize/sauvola.go
index ca0acf0..ee773ba 100644
--- a/binarize/sauvola.go
+++ b/binarize/sauvola.go
@@ -28,7 +28,7 @@ func Sauvola(img *image.Gray, ksize float64, windowsize int) *image.Gray {
 }
 
 // Implements Sauvola's algorithm using Integral Images, see paper
-// "Effcient Implementation of Local Adaptive Thresholding Techniques Using Integral Images"
+// "Efficient Implementation of Local Adaptive Thresholding Techniques Using Integral Images"
 // and
 // https://stackoverflow.com/questions/13110733/computing-image-integral
 func IntegralSauvola(img *image.Gray, ksize float64, windowsize int) *image.Gray {
diff --git a/binarize/util.go b/binarize/util.go
index e7fcfe4..ad641c9 100644
--- a/binarize/util.go
+++ b/binarize/util.go
@@ -1,6 +1,7 @@
 package binarize
 
 import (
+	"errors"
 	"image"
 	"math"
 )
@@ -65,3 +66,22 @@ func surrounding(img *image.Gray, x int, y int, size int) []int {
 	}
 	return s
 }
+
+func BinToZeroInv(bin *image.Gray, orig *image.RGBA) (*image.RGBA, error) {
+	b := bin.Bounds()
+	if ! b.Eq(orig.Bounds()) {
+		return orig, errors.New("bin and orig images need to be the same dimensions")
+	}
+	newimg := image.NewRGBA(image.Rect(0, 0, b.Dx(), b.Dy()))
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x++ {
+			if bin.GrayAt(x, y).Y == 255 {
+				newimg.Set(x, y, bin.GrayAt(x, y))
+			} else {
+				newimg.Set(x, y, orig.At(x, y))
+			}
+		}
+	}
+
+	return newimg, nil
+}