diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4315289..14e8d36 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -4,12 +4,12 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.6.x, 1.7.x, 1.8.x, 1.9.x, 1.10.x, 1.11.x, 1.12.x, 1.13.x, 1.14.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x]
+        go-version: [1.6.x, 1.7.x, 1.8.x, 1.9.x, 1.10.x, 1.11.x, 1.12.x, 1.13.x, 1.14.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x, 1.19.x, 1.20.x]
         platform: [ubuntu-latest]
     runs-on: ${{ matrix.platform }}
     steps:
     - name: Install Go
-      uses: actions/setup-go@v1
+      uses: actions/setup-go@v4
       with:
         go-version: ${{ matrix.go-version }}
     - name: Set GOPATH
diff --git a/.github/workflows/ci_gomodule.yml b/.github/workflows/ci_gomodule.yml
index 1bf31c5..8ff0aeb 100644
--- a/.github/workflows/ci_gomodule.yml
+++ b/.github/workflows/ci_gomodule.yml
@@ -4,12 +4,12 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.11.x, 1.12.x, 1.13.x, 1.14.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x]
+        go-version: [1.11.x, 1.12.x, 1.13.x, 1.14.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x, 1.19.x, 1.20.x]
         platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
     steps:
     - name: Install Go
-      uses: actions/setup-go@v1
+      uses: actions/setup-go@v4
       with:
         go-version: ${{ matrix.go-version }}
     - name: Checkout code
diff --git a/.gitignore b/.gitignore
index a1338d6..198fc00 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,7 @@
 
 # Output of the go coverage tool, specifically when used with LiteIDE
 *.out
+*.html
 
 # Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736
 .glide/
diff --git a/go.mod b/go.mod
index 681fdc2..94bd86e 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module github.com/corona10/goimagehash
 
+go 1.11
+
 require github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646
diff --git a/hashcompute.go b/hashcompute.go
index e1ac427..f964285 100644
--- a/hashcompute.go
+++ b/hashcompute.go
@@ -14,7 +14,7 @@ import (
 	"github.com/nfnt/resize"
 )
 
-// AverageHash fuction returns a hash computation of average hash.
+// AverageHash function returns a hash computation of average hash.
 // Implementation follows
 // http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html
 func AverageHash(img image.Image) (*ImageHash, error) {
diff --git a/hashcompute_test.go b/hashcompute_test.go
index 83711a9..6d77834 100644
--- a/hashcompute_test.go
+++ b/hashcompute_test.go
@@ -124,6 +124,34 @@ func TestNilHashCompute(t *testing.T) {
 	}
 }
 
+func TestExtendHashCompute(t *testing.T) {
+	file, err := os.Open("_examples/sample1.jpg")
+	if err != nil {
+		t.Errorf("%s", err)
+	}
+	defer file.Close()
+	img, err := jpeg.Decode(file)
+	if err != nil {
+		t.Errorf("%s", err)
+	}
+
+	hash, err := ExtPerceptionHash(img, 0, 8)
+	if err == nil {
+		t.Errorf("Error should be got.")
+	}
+	if hash != nil {
+		t.Errorf("Nil hash should be got. but got %v", hash)
+	}
+
+	hash, err = ExtPerceptionHash(img, 16, 2)
+	if err != nil {
+		t.Errorf("%s", err)
+	}
+	if hash == nil {
+		t.Errorf("Hash should be got.")
+	}
+}
+
 func TestNilExtendHashCompute(t *testing.T) {
 	hash, err := ExtAverageHash(nil, 8, 8)
 	if err == nil {
@@ -348,7 +376,7 @@ func BenchmarkAverageHash(b *testing.B) {
 	}
 }
 
-func BenchmarkDiffrenceHash(b *testing.B) {
+func BenchmarkDifferenceHash(b *testing.B) {
 	file1, err := os.Open("_examples/sample3.jpg")
 	if err != nil {
 		b.Errorf("%s", err)
diff --git a/imagehash_test.go b/imagehash_test.go
index da9dd5b..93ebf21 100644
--- a/imagehash_test.go
+++ b/imagehash_test.go
@@ -66,6 +66,9 @@ func TestSerialization(t *testing.T) {
 	methods := []func(img image.Image) (*ImageHash, error){
 		AverageHash, PerceptionHash, DifferenceHash,
 	}
+	extMethods := []func(img image.Image, width int, height int) (*ExtImageHash, error){
+		ExtAverageHash, ExtPerceptionHash, ExtDifferenceHash,
+	}
 	examples := []string{
 		"_examples/sample1.jpg", "_examples/sample2.jpg", "_examples/sample3.jpg", "_examples/sample4.jpg",
 	}
@@ -103,28 +106,50 @@ func TestSerialization(t *testing.T) {
 		}
 
 		// test for ExtIExtImageHash
-		sizeList := []int{8, 16}
-		for _, size := range sizeList {
-			hash, err := ExtPerceptionHash(img, size, size)
-			checkErr(err)
+		for _, extMethod := range extMethods {
+			extMethodStr := runtime.FuncForPC(reflect.ValueOf(extMethod).Pointer()).Name()
+			sizeList := []int{8, 16}
+			for _, size := range sizeList {
+				hash, err := extMethod(img, size, size)
+				checkErr(err)
 
-			hex := hash.ToString()
-			// len(kind) == 1, len(":") == 1
-			if len(hex) != size*size/4+2 {
-				t.Errorf("Got invalid hex string '%v'; %v of '%v'", hex, "ExtPerceptionHash", ex)
-			}
+				hex := hash.ToString()
+				// len(kind) == 1, len(":") == 1
+				if len(hex) != size*size/4+2 {
+					t.Errorf("Got invalid hex string '%v'; %v of '%v'", hex, extMethodStr, ex)
+				}
 
-			reHash, err := ExtImageHashFromString(hex)
-			checkErr(err)
+				reHash, err := ExtImageHashFromString(hex)
+				checkErr(err)
 
-			distance, err := hash.Distance(reHash)
-			checkErr(err)
+				distance, err := hash.Distance(reHash)
+				checkErr(err)
 
-			if distance != 0 {
-				t.Errorf("Original and unserialized objects should be identical, got distance=%v; %v of '%v'", distance, "ExtPerceptionHash", ex)
+				if distance != 0 {
+					t.Errorf("Original and unserialized objects should be identical, got distance=%v; %v of '%v'", distance, "ExtPerceptionHash", ex)
+				}
 			}
 		}
 	}
+
+	// test for hashing empty string
+	imageHash, err := ImageHashFromString("")
+	if imageHash != nil {
+		t.Errorf("Expected reHash to be nil, got %v", imageHash)
+	}
+	if err == nil {
+		t.Errorf("Should got error for empty string")
+	}
+	extImageHash, err := ExtImageHashFromString("")
+	if extImageHash != nil {
+		t.Errorf("Expected reHash to be nil, got %v", extImageHash)
+	}
+	if err == nil {
+		t.Errorf("Should got error for empty string")
+	}
+
+	// test for hashing invalid (non-hexadecimal) string
+	extImageHash, err = ExtImageHashFromString("k:g")
 }
 
 func TestDifferentBitSizeHash(t *testing.T) {
@@ -231,4 +256,16 @@ func TestDumpAndLoad(t *testing.T) {
 			}
 		}
 	}
+
+	// test for loading empty bytes buffer
+	var b bytes.Buffer
+	bar := bufio.NewReader(&b)
+	_, err := LoadImageHash(bar)
+	if err == nil {
+		t.Errorf("Should got error for empty bytes buffer")
+	}
+	_, err = LoadExtImageHash(bar)
+	if err == nil {
+		t.Errorf("Should got error for empty bytes buffer")
+	}
 }
diff --git a/transforms/dct.go b/transforms/dct.go
index 1cc9645..9916467 100644
--- a/transforms/dct.go
+++ b/transforms/dct.go
@@ -37,7 +37,7 @@ func forwardTransform(input, temp []float64, Len int) {
 	input[Len-2], input[Len-1] = temp[halfLen-1], temp[Len-1]
 }
 
-// DCT2D function returns a  result of DCT2D by using the seperable property.
+// DCT2D function returns a  result of DCT2D by using the separable property.
 func DCT2D(input [][]float64, w int, h int) [][]float64 {
 	output := make([][]float64, h)
 	for i := range output {
@@ -74,7 +74,7 @@ func DCT2D(input [][]float64, w int, h int) [][]float64 {
 	return output
 }
 
-// DCT2DFast64 function returns a result of DCT2D by using the seperable property.
+// DCT2DFast64 function returns a result of DCT2D by using the separable property.
 // Fast uses static DCT tables for improved performance. Returns flattened pixels.
 func DCT2DFast64(input *[]float64) (flattens [64]float64) {
 	if len(*input) != 64*64 {
@@ -98,7 +98,7 @@ func DCT2DFast64(input *[]float64) (flattens [64]float64) {
 	return
 }
 
-// DCT2DFast256 function returns a result of DCT2D by using the seperable property.
+// DCT2DFast256 function returns a result of DCT2D by using the separable property.
 // DCT type II, unscaled. Algorithm by Byeong Gi Lee, 1984.
 // Fast uses static DCT tables for improved performance. Returns flattened pixels.
 func DCT2DFast256(input *[]float64) (flattens [256]float64) {
diff --git a/transforms/pixels.go b/transforms/pixels.go
index be82b86..82bdb0d 100644
--- a/transforms/pixels.go
+++ b/transforms/pixels.go
@@ -58,7 +58,7 @@ func rgb2GrayDefault(colorImg image.Image, pixels []float64, s int) {
 	}
 }
 
-// rgb2GrayYCbCR uses *image.YCbCr which is signifiantly faster than the image.Image interface.
+// rgb2GrayYCbCR uses *image.YCbCr which is significantly faster than the image.Image interface.
 func rgb2GrayYCbCR(colorImg *image.YCbCr, pixels []float64, s int) {
 	for i := 0; i < s; i++ {
 		for j := 0; j < s; j++ {
@@ -67,7 +67,7 @@ func rgb2GrayYCbCR(colorImg *image.YCbCr, pixels []float64, s int) {
 	}
 }
 
-// rgb2GrayYCbCR uses *image.RGBA which is signifiantly faster than the image.Image interface.
+// rgb2GrayRGBA uses *image.RGBA which is significantly faster than the image.Image interface.
 func rgb2GrayRGBA(colorImg *image.RGBA, pixels []float64, s int) {
 	for i := 0; i < s; i++ {
 		for j := 0; j < s; j++ {