From 5f56e8609c1304c9019888e3716109654d00b80c Mon Sep 17 00:00:00 2001
From: Dong-hee Na <donghee.na92@gmail.com>
Date: Sat, 16 Mar 2019 00:47:57 +0900
Subject: [PATCH] DifferenceHashExtend: Implement DifferenceHashExtend (#21)

---
 hashcompute.go      | 28 ++++++++++++++++++++++++++++
 hashcompute_test.go | 13 +++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/hashcompute.go b/hashcompute.go
index abf2aae..4fcd405 100644
--- a/hashcompute.go
+++ b/hashcompute.go
@@ -135,3 +135,31 @@ func AverageHashExtend(img image.Image, hashSize int) (*ExtImageHash, error) {
 	}
 	return NewExtImageHash(ahash, AHash), nil
 }
+
+// DifferenceHashExtend function returns dhash of which the size can be set larger than uint64
+// Support 64bits dhash (hashSize=8) and 256bits dhash (hashSize=16)
+func DifferenceHashExtend(img image.Image, hashSize int) (*ExtImageHash, error) {
+	if img == nil {
+		return nil, errors.New("Image object can not be nil")
+	}
+
+	imgSize := hashSize * hashSize
+
+	resized := resize.Resize(uint(hashSize)+1, uint(hashSize), img, resize.Bilinear)
+	pixels := transforms.Rgb2Gray(resized)
+
+	lenOfUnit := 64
+	dhash := make([]uint64, imgSize/lenOfUnit)
+	idx := 0
+	for i := 0; i < len(pixels); i++ {
+		for j := 0; j < len(pixels[i])-1; j++ {
+			indexOfArray := (imgSize - 1 - idx) / lenOfUnit
+			indexOfBit := idx % lenOfUnit
+			if pixels[i][j] < pixels[i][j+1] {
+				dhash[indexOfArray] |= 1 << uint(indexOfBit)
+			}
+			idx++
+		}
+	}
+	return NewExtImageHash(dhash, DHash), nil
+}
diff --git a/hashcompute_test.go b/hashcompute_test.go
index b058fb2..e77f8df 100644
--- a/hashcompute_test.go
+++ b/hashcompute_test.go
@@ -177,6 +177,19 @@ func TestExtImageHashCompute(t *testing.T) {
 		{"_examples/sample2.jpg", "_examples/sample2.jpg", 16, PerceptionHashExtend, "PerceptionHashExtend", 0},
 		{"_examples/sample3.jpg", "_examples/sample3.jpg", 16, PerceptionHashExtend, "PerceptionHashExtend", 0},
 		{"_examples/sample4.jpg", "_examples/sample4.jpg", 16, PerceptionHashExtend, "PerceptionHashExtend", 0},
+		{"_examples/sample1.jpg", "_examples/sample1.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample2.jpg", "_examples/sample2.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample3.jpg", "_examples/sample3.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample4.jpg", "_examples/sample4.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample1.jpg", "_examples/sample2.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 43},
+		{"_examples/sample1.jpg", "_examples/sample3.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample1.jpg", "_examples/sample4.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 37},
+		{"_examples/sample2.jpg", "_examples/sample3.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 43},
+		{"_examples/sample2.jpg", "_examples/sample4.jpg", 8, DifferenceHashExtend, "DifferenceHashExtend", 16},
+		{"_examples/sample1.jpg", "_examples/sample1.jpg", 16, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample2.jpg", "_examples/sample2.jpg", 16, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample3.jpg", "_examples/sample3.jpg", 16, DifferenceHashExtend, "DifferenceHashExtend", 0},
+		{"_examples/sample4.jpg", "_examples/sample4.jpg", 16, DifferenceHashExtend, "DifferenceHashExtend", 0},
 	} {
 		file1, err := os.Open(tt.img1)
 		if err != nil {