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Using NRGBA (alpha-premultiplied color)
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This avoids a few possible apha channel issues.
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@auyer
auyer committed Jul 28, 2021
1 parent 74a088c commit a39bbff
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Showing 2 changed files with 30 additions and 30 deletions.
50 changes: 25 additions & 25 deletions steganography.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -11,23 +11,23 @@ import (
"image/png"
)

// EncodeRGBA encodes a given string into the input image using least significant bit encryption (LSB steganography)
// EncodeNRGBA encodes a given string into the input image using least significant bit encryption (LSB steganography)
// The minnimum image size is 24 pixels for one byte. For each additional byte, it is necessary 3 more pixels.
/*
Input:
writeBuffer *bytes.Buffer : the destination of the encoded image bytes
pictureInputFile image.RGBA : image data used in encoding
pictureInputFile image.NRGBA : image data used in encoding
message []byte : byte slice of the message to be encoded
Output:
bytes buffer ( io.writter ) to create file, or send data.
*/
func EncodeRGBA(writeBuffer *bytes.Buffer, rgbImage *image.RGBA, message []byte) error {
func EncodeNRGBA(writeBuffer *bytes.Buffer, rgbImage *image.NRGBA, message []byte) error {

var messageLength = uint32(len(message))

var width = rgbImage.Bounds().Dx()
var height = rgbImage.Bounds().Dy()
var c color.RGBA
var c color.NRGBA
var bit byte
var ok bool
//var encodedImage image.Image
Expand All @@ -49,12 +49,12 @@ func EncodeRGBA(writeBuffer *bytes.Buffer, rgbImage *image.RGBA, message []byte)
for x := 0; x < width; x++ {
for y := 0; y < height; y++ {

c = rgbImage.RGBAAt(x, y) // get the color at this pixel
c = rgbImage.NRGBAAt(x, y) // get the color at this pixel

/* RED */
bit, ok = <-ch
if !ok { // if we don't have any more bits left in our message
rgbImage.SetRGBA(x, y, c)
rgbImage.SetNRGBA(x, y, c)
png.Encode(writeBuffer, rgbImage)
// return *writeBuffer, nil
}
Expand All @@ -63,7 +63,7 @@ func EncodeRGBA(writeBuffer *bytes.Buffer, rgbImage *image.RGBA, message []byte)
/* GREEN */
bit, ok = <-ch
if !ok {
rgbImage.SetRGBA(x, y, c)
rgbImage.SetNRGBA(x, y, c)
png.Encode(writeBuffer, rgbImage)
return nil
}
Expand All @@ -72,13 +72,13 @@ func EncodeRGBA(writeBuffer *bytes.Buffer, rgbImage *image.RGBA, message []byte)
/* BLUE */
bit, ok = <-ch
if !ok {
rgbImage.SetRGBA(x, y, c)
rgbImage.SetNRGBA(x, y, c)
png.Encode(writeBuffer, rgbImage)
return nil
}
setLSB(&c.B, bit)

rgbImage.SetRGBA(x, y, c)
rgbImage.SetNRGBA(x, y, c)
}
}

Expand All @@ -89,7 +89,7 @@ func EncodeRGBA(writeBuffer *bytes.Buffer, rgbImage *image.RGBA, message []byte)

// Encode encodes a given string into the input image using least significant bit encryption (LSB steganography)
// The minnimum image size is 23 pixels
// It wraps EncodeRGBA making the conversion from image.Image to image.RGBA
// It wraps EncodeNRGBA making the conversion from image.Image to image.NRGBA
/*
Input:
writeBuffer *bytes.Buffer : the destination of the encoded image bytes
Expand All @@ -100,30 +100,30 @@ func EncodeRGBA(writeBuffer *bytes.Buffer, rgbImage *image.RGBA, message []byte)
*/
func Encode(writeBuffer *bytes.Buffer, pictureInputFile image.Image, message []byte) error {

rgbImage := imageToRGBA(pictureInputFile)
rgbImage := imageToNRGBA(pictureInputFile)

return EncodeRGBA(writeBuffer, rgbImage, message)
return EncodeNRGBA(writeBuffer, rgbImage, message)

}

// decodeRGBA gets messages from pictures using LSB steganography, decode the message from the picture and return it as a sequence of bytes
// decodeNRGBA gets messages from pictures using LSB steganography, decode the message from the picture and return it as a sequence of bytes
/*
Input:
startOffset uint32 : number of bytes used to declare size of message
msgLen uint32 : size of the message to be decoded
pictureInputFile image.RGBA : image data used in decoding
pictureInputFile image.NRGBA : image data used in decoding
Output:
message []byte decoded from image
*/
func decodeRGBA(startOffset uint32, msgLen uint32, rgbImage *image.RGBA) (message []byte) {
func decodeNRGBA(startOffset uint32, msgLen uint32, rgbImage *image.NRGBA) (message []byte) {

var byteIndex uint32
var bitIndex uint32

width := rgbImage.Bounds().Dx()
height := rgbImage.Bounds().Dy()

var c color.RGBA
var c color.NRGBA
var lsb byte

message = append(message, 0)
Expand All @@ -132,7 +132,7 @@ func decodeRGBA(startOffset uint32, msgLen uint32, rgbImage *image.RGBA) (messag
for x := 0; x < width; x++ {
for y := 0; y < height; y++ {

c = rgbImage.RGBAAt(x, y) // get the color of the pixel
c = rgbImage.NRGBAAt(x, y) // get the color of the pixel

/* RED */
lsb = getLSB(c.R) // get the least significant bit from the red component of this pixel
Expand Down Expand Up @@ -188,7 +188,7 @@ func decodeRGBA(startOffset uint32, msgLen uint32, rgbImage *image.RGBA) (messag
}

// decode gets messages from pictures using LSB steganography, decode the message from the picture and return it as a sequence of bytes
// It wraps EncodeRGBA making the conversion from image.Image to image.RGBA
// It wraps EncodeNRGBA making the conversion from image.Image to image.NRGBA
/*
Input:
startOffset uint32 : number of bytes used to declare size of message
Expand All @@ -199,13 +199,13 @@ func decodeRGBA(startOffset uint32, msgLen uint32, rgbImage *image.RGBA) (messag
*/
func decode(startOffset uint32, msgLen uint32, pictureInputFile image.Image) (message []byte) {

rgbImage := imageToRGBA(pictureInputFile)
return decodeRGBA(startOffset, msgLen, rgbImage)
rgbImage := imageToNRGBA(pictureInputFile)
return decodeNRGBA(startOffset, msgLen, rgbImage)

}

// Decode gets messages from pictures using LSB steganography, decode the message from the picture and return it as a sequence of bytes
// It wraps EncodeRGBA making the conversion from image.Image to image.RGBA
// It wraps EncodeNRGBA making the conversion from image.Image to image.NRGBA
/*
Input:
msgLen uint32 : size of the message to be decoded
Expand Down Expand Up @@ -334,17 +334,17 @@ func splitToBytes(x uint32) (one, two, three, four byte) {
return
}

// imageToRGBA converts image.Image to image.RGBA
func imageToRGBA(src image.Image) *image.RGBA {
// imageToNRGBA converts image.Image to image.NRGBA
func imageToNRGBA(src image.Image) *image.NRGBA {
bounds := src.Bounds()

var m *image.RGBA
var m *image.NRGBA
var width, height int

width = bounds.Dx()
height = bounds.Dy()

m = image.NewRGBA(image.Rect(0, 0, width, height))
m = image.NewNRGBA(image.Rect(0, 0, width, height))

draw.Draw(m, m.Bounds(), src, bounds.Min, draw.Src)
return m
Expand Down
10 changes: 5 additions & 5 deletions steganography_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -144,7 +144,7 @@ func TestEncodeDecodeGeneratedSmallImage(t *testing.T) {
upLeft := image.Point{0, 0}
lowRight := image.Point{width, height}

newimg := image.NewRGBA(image.Rectangle{upLeft, lowRight})
newimg := image.NewNRGBA(image.Rectangle{upLeft, lowRight})

// Set color for each pixel.
for x := 0; x < width; x++ {
Expand All @@ -154,7 +154,7 @@ func TestEncodeDecodeGeneratedSmallImage(t *testing.T) {
}

w := new(bytes.Buffer)
err := EncodeRGBA(w, newimg, []uint8{84, 84, 84}) // Encode the message into the image file
err := EncodeNRGBA(w, newimg, []uint8{84, 84, 84}) // Encode the message into the image file
if err != nil {
log.Printf("Error Encoding file %v", err)
t.FailNow()
Expand All @@ -180,14 +180,14 @@ func TestEncodeDecodeGeneratedSmallImage(t *testing.T) {
}
func TestSmalImage(t *testing.T) {

miniImage := image.Image(image.NewRGBA(image.Rectangle{image.Point{0, 0}, image.Point{18, 1}}))
miniImage := image.Image(image.NewNRGBA(image.Rectangle{image.Point{0, 0}, image.Point{18, 1}}))
log.Print(MaxEncodeSize(miniImage))
if MaxEncodeSize(miniImage) > 0 {
log.Printf("Uncaught small image size")
t.FailNow()
}

miniImage = image.Image(image.NewRGBA(image.Rectangle{image.Point{0, 0}, image.Point{23, 1}}))
miniImage = image.Image(image.NewNRGBA(image.Rectangle{image.Point{0, 0}, image.Point{23, 1}}))

if MaxEncodeSize(miniImage) != 4 {
log.Printf("Uncaught minimal image size")
Expand All @@ -197,7 +197,7 @@ func TestSmalImage(t *testing.T) {

func TestMessageTooLarge(t *testing.T) {

miniImage := image.Image(image.NewRGBA(image.Rectangle{image.Point{0, 0}, image.Point{24, 1}}))
miniImage := image.Image(image.NewNRGBA(image.Rectangle{image.Point{0, 0}, image.Point{24, 1}}))
w := new(bytes.Buffer)
err := Encode(w, miniImage, bitmessage) // Encode the message into the image file
if err == nil {
Expand Down

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