Separate out binarize into a package, and start adding tests for it

1 files changed, 88 insertions, 0 deletions

diff --git a/binarize/sauvola_test.go b/binarize/sauvola_test.go
new file mode 100644
index 0000000..12a040a
--- /dev/null
+++ b/binarize/sauvola_test.go
@@ -0,0 +1,88 @@
+package binarize
+
+import (
+	"fmt"
+	"image"
+	"image/draw"
+	"image/png"
+	"os"
+	"testing"
+)
+
+func decode(s string) (*image.Gray, error) {
+	f, err := os.Open(s)
+	defer f.Close()
+	if err != nil {
+		return nil, err
+	}
+	img, err := png.Decode(f)
+	if err != nil {
+		return nil, err
+	}
+	b := img.Bounds()
+	gray := image.NewGray(image.Rect(0, 0, b.Dx(), b.Dy()))
+	draw.Draw(gray, b, img, b.Min, draw.Src)
+	return gray, nil
+}
+
+func imgsequal(img1 *image.Gray, img2 *image.Gray) bool {
+	b := img1.Bounds()
+	if ! b.Eq(img2.Bounds())  {
+		return false
+	}
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x++ {
+			r0, g0, b0, a0 := img1.At(x, y).RGBA()
+			r1, g1, b1, a1 := img2.At(x, y).RGBA()
+			if r0 != r1 {
+				return false
+			}
+			if g0 != g1 {
+				return false
+			}
+			if b0 != b1 {
+				return false
+			}
+			if a0 != a1 {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+func TestBinarization(t *testing.T) {
+	// TODO: test non-integral sauvola method too
+	cases := []struct {
+		name string
+		orig string
+		done string
+		ksize float64
+		wsize int
+	}{
+		{"integralsauvola", "testdata/pg1.png", "testdata/pg1_integralsauvola_k0.5_w41.png", 0.5, 41},
+		{"integralsauvola", "testdata/pg1.png", "testdata/pg1_integralsauvola_k0.5_w19.png", 0.5, 19},
+		{"integralsauvola", "testdata/pg1.png", "testdata/pg1_integralsauvola_k0.3_w19.png", 0.3, 19},
+	}
+
+	for _, c := range cases {
+		t.Run(fmt.Sprintf("%s_%0.1f_%d", c.name, c.ksize, c.wsize), func(t *testing.T) {
+			orig, err := decode(c.orig)
+			if err != nil {
+				t.Errorf("Could not open file %s: %v\n", c.orig, err)
+			}
+			done, err := decode(c.done)
+			if err != nil {
+				t.Errorf("Could not open file %s: %v\n", c.done, err)
+			}
+			new := IntegralSauvola(orig, c.ksize, c.wsize)
+			if ! imgsequal(done, new) {
+				t.Errorf("Binarized %s differs to %s\n", c.orig, c.done)
+			}
+		})
+	}
+}
+
+func TestIntegralImg(t *testing.T) {
+	// TODO: compare mean and stddev between integral and basic methods
+}