diff --git a/README.md b/README.md
index 00662cc..bbb810c 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,6 @@
 [![Build Status](https://travis-ci.org/corona10/goimagehash.svg?branch=master)](https://travis-ci.org/corona10/goimagehash)
 [![GoDoc](https://godoc.org/github.com/corona10/goimagehash?status.svg)](https://godoc.org/github.com/corona10/goimagehash)
+[![Go Report Card](https://goreportcard.com/badge/github.com/corona10/goimagehash)](https://goreportcard.com/report/github.com/corona10/goimagehash)
 
 # goimagehash
 > Inspired by [imagehash](https://github.com/JohannesBuchner/imagehash)
diff --git a/etcs/utils.go b/etcs/utils.go
index 1c9249d..c75133d 100644
--- a/etcs/utils.go
+++ b/etcs/utils.go
@@ -4,7 +4,7 @@
 
 package etcs
 
-// Calculate mean of pixels.
+// MeanOfPixels function returns a mean of pixels.
 func MeanOfPixels(pixels []float64) float64 {
 	m := 0.0
 	lens := len(pixels)
@@ -19,8 +19,8 @@ func MeanOfPixels(pixels []float64) float64 {
 	return m / float64(lens)
 }
 
-// Get a median value of pixels.
-// Use quick selection algorithm.
+// MedianOfPixels function returns a median value of pixels.
+// It uses quick selection algorithm.
 func MedianOfPixels(pixels []float64) float64 {
 	tmp := make([]float64, len(pixels))
 	copy(tmp, pixels)
diff --git a/hashcompute.go b/hashcompute.go
index a528908..490a6bc 100644
--- a/hashcompute.go
+++ b/hashcompute.go
@@ -13,8 +13,7 @@ import (
 	"github.com/nfnt/resize"
 )
 
-// Average Hash computation.
-// Return 64bits hash.
+// AverageHash fuction 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) {
@@ -38,7 +37,7 @@ func AverageHash(img image.Image) (*ImageHash, error) {
 	return ahash, nil
 }
 
-// Difference Hash computation.
+// DifferenceHash function returns a hash computation of difference hash.
 // Implementation follows
 // http://www.hackerfactor.com/blog/?/archives/529-Kind-of-Like-That.html
 func DifferenceHash(img image.Image) (*ImageHash, error) {
@@ -62,7 +61,7 @@ func DifferenceHash(img image.Image) (*ImageHash, error) {
 	return dhash, nil
 }
 
-// Perceptual Hash computation.
+// PerceptionHash function returns a hash computation of phash.
 // Implementation follows
 // http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html
 func PerceptionHash(img image.Image) (*ImageHash, error) {
diff --git a/imagehash.go b/imagehash.go
index 1b02809..0db84c0 100644
--- a/imagehash.go
+++ b/imagehash.go
@@ -11,25 +11,26 @@ import (
 // hashKind describes the kinds of hash.
 type hashKind int
 
+// ImageHash is a struct of hash computation.
 type ImageHash struct {
 	hash uint64
 	kind hashKind
 }
 
 const (
-	Unknown hashKind = iota
-	AHash            // Average Hash
-	PHash            // Perceptual Hash
-	DHash            // Difference Hash
-	WHash            // Wavlet Hash
+	Unknown hashKind = iota // Unknown Hash
+	AHash                   // Average Hash
+	PHash                   // Perceptual Hash
+	DHash                   // Difference Hash
+	WHash                   // Wavlet Hash
 )
 
-// Create a new image hash.
+// NewImageHash function creates a new image hash.
 func NewImageHash(hash uint64, kind hashKind) *ImageHash {
 	return &ImageHash{hash: hash, kind: kind}
 }
 
-// Return distance between hashes.
+// Distance method returns a distance between two hashes.
 func (h *ImageHash) Distance(other *ImageHash) (int, error) {
 	if h.GetKind() != other.GetKind() {
 		return -1, errors.New("Image hashes's kind should be identical.")
@@ -48,17 +49,17 @@ func (h *ImageHash) Distance(other *ImageHash) (int, error) {
 	return diff, nil
 }
 
-// Return hash values.
+// GetHash method returns a 64bits hash value.
 func (h *ImageHash) GetHash() uint64 {
 	return h.hash
 }
 
-// Get kind of a hash.
+// GetKind method returns a kind of image hash.
 func (h *ImageHash) GetKind() hashKind {
 	return h.kind
 }
 
-// Set index of bits.
+// Set method sets a bit of index.
 func (h *ImageHash) Set(idx int) {
 	h.hash |= 1 << uint(idx)
 }
diff --git a/transforms/dct.go b/transforms/dct.go
index b7a00e6..e3de089 100644
--- a/transforms/dct.go
+++ b/transforms/dct.go
@@ -8,7 +8,7 @@ import (
 	"math"
 )
 
-// Get result of DCT-II.
+// DCT1D function returns result of DCT-II.
 // Follows Matlab dct().
 // Implementation reference:
 // https://unix4lyfe.org/dct-1d/
@@ -30,7 +30,7 @@ func DCT1D(input []float64) []float64 {
 	return out
 }
 
-// Get result of DCT2D by using the seperable property.
+// DCT2D function returns a  result of DCT2D by using the seperable property.
 func DCT2D(input [][]float64, w int, h int) [][]float64 {
 	output := make([][]float64, h)
 	for i := range output {
diff --git a/transforms/pixels.go b/transforms/pixels.go
index 1b93b60..744c4ac 100644
--- a/transforms/pixels.go
+++ b/transforms/pixels.go
@@ -8,7 +8,7 @@ import (
 	"image"
 )
 
-// Convert RGB to a gray scale flatten array.
+// Rgb2Gray function converts RGB to a gray scale array.
 func Rgb2Gray(colorImg image.Image) [][]float64 {
 	bounds := colorImg.Bounds()
 	w, h := bounds.Max.X, bounds.Max.Y
@@ -27,6 +27,7 @@ func Rgb2Gray(colorImg image.Image) [][]float64 {
 	return pixels
 }
 
+// FlattenPixels function flattens 2d array into 1d array.
 func FlattenPixels(pixels [][]float64, x int, y int) []float64 {
 	flattens := make([]float64, x*y)
 	for i := 0; i < y; i++ {