写入JPEG文件
我在JPEG图片上执行隐写。我使用DCT系数来隐藏数据。我执行以下步骤：
- 将输入图像读入
BufferedImage - 从
BufferedImage获取8 x 8块
- 应用前向DCT以获得DCT系数
- 在DCT系数中嵌入消息位
- 应用反DCT并将块写回
BufferedImage
重复步骤2-5，直到没有剩余消息位，此时我将BufferedImage写入名为output.jpg的JPEG文件。值得一提的是，我不对整个图像应用DCT，而只对我嵌入消息位的块应用ouput.jpg。我正在使用this来源进行DCT，使用this来进行隐写术
问题：我最终得到static int[][] DCT_coefficients = new int[8][8];
static double[][] DCT_matrix = new double[8][8];
static int[][] Dequantized_m = new int[8][8];
static int[][] YBlock = new int[8][8];
static double[][] resultant = new double[8][8];
static int[][] red = new int[8][8];
static int[][] green = new int[8][8];
static int[][] blue = new int[8][8];
static int[][] Y = new int[8][8];
static int[][] Cb = new int[8][8];
static int[][] Cr = new int[8][8];
static int x = 0, y = 0;
public static void main(String args[]) {
//I retrieve a pixel block from **BufferedImage** and convert it to YCbCr
double temp1, temp2, temp3, temp4;
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
Color c = new Color(input_image.getRGB(y, x));
red = c.getRed();
green = c.getGreen();
blue = c.getBlue();
YCbCr = YCrCb_conversion(red, green, blue);
YBlock[i][j] = YCbCr[0];
Cb[i][j] = YCbCr[1];
Cr[i][j] = YCbCr[2];
y++;
}
x++;
}
//calculating DCT matrix
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
if (i == 0) {
DCT_matrix[i][j] = 1 / Math.sqrt(8.0);
}
if (i > 0) {
temp1 = 0.5;
Apfloat Atemp1 = new Apfloat(temp1, 15);
temp3 = ((2 * j) + 1) * i * java.lang.Math.PI;
temp2 = temp3 / 16;
Apfloat Atemp2 = new Apfloat(temp2, 15);
temp4 = Math.cos(java.lang.Math.toRadians(temp2));
Apfloat Atemp4 = ApfloatMath.cos(Atemp2);
Apfloat Atemp = Atemp4.multiply(Atemp1);
DCT_matrix[i][j] = Atemp.doubleValue();
}
}
}
//Leveling off Yblock
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
leveledoff[i][j] = pixel_block[i][j] - 128;
}
}
// multiplying DCT matrix and leveled off YBlock
resultant = matrix_multiply(DCT_matrix, leveledoff);
// taking transpose of DCT matrix
transpose = obj.transpose(DCT_matrix);
//multiplying transpose with resultant to get DCT coefficient block
DCT_Coefficients = matrix_multiply(resultant, trans);
//quantizing DCT coefficients using 50 % quantization matrix
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
quantized_matrix[i][j] = (int) Math.round(DCT_Coefficients[i][j] / quantzation_matrix[i][j]);
}
}
//Applying zigzag encoding
ZigZag_encoded = zigzag.ZigzagEncode(quantised_m);
//Encode data
ZigZag_encoded = embed_data(ZigZag_encoded, data_buffer);
//start IDCT
IDCT(ZigZag_Encoded);
//end main
}
//Method definitions
//Method to change LSB of integer value
public static int changeBit(int pixel, char bit) {
String s = Integer.toBinaryString(pixel);
char[] c = s.toCharArray();
c[c.length - 1] = bit;
// converting binary to integer
String n = "";
for (int y = 0; y < c.length; y++) {
n += "" + c[y];
}
int j = 0;
for (int i = 0; i < n.length(); i++) {
if (n.charAt(i) == '1') {
j = j + pow(2, n.length() - 1 - i);
}
}
return j;
}
// method to embed data
public static int[] embed_data(int encoded[], char buffer[]) {
for (int i = 0; i < buffer.length; i++) {
int newVal = changeBit(encoded[i], buffer[i]);
encoded[i] = newVal;
}
return encoded;
}
// Method to perform IDCT
public static void IDCT(ZigZag_encoded) {
//converting 1D zigzag array to 2D array
quantised_matrix = Zigzag_Decode(ZigZag_encoded);
//Dequantizing
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
Dequantized[i][j] = quantised_matrix[i][j] * quantzation_matrix[i][j];
}
}
// multiplying transpose of DCT matrix with Dequantized matrix
resultant = matrix_multiply(transpose, Dequantized);
//multiplying resultant with DCT matrix
resultant = matrix_multiply(resultant, dct_mat);
//adding 128 to each resultant entry and rounding off
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
block[i][j] = (int) Math.round(resultant[i][j] + 128);
}
}
//Converting Yblock to RGB block
YCrCbToRGB(block, Cb, Cr);
//writing RGB block to BufferedImage
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
newcolor = new Color(red[i][j], green[i][j], blue[i][j]);
input_image.setRGB(y, x, newcolor.getRGB());
y++;
}
x++;
}
}
//method to convert RGB block to YCbCr
public int[] YCrCb_conversion(int red, int green, int blue) {
int[] YCbCr = new int[3];
//Y = 0.257R+ 0.504G + 0.098B + 16
YCbCr[0] = (int)(0.257 * red + 0.504 * green + 0.098 * blue) + 16;
//Cb=–0.148R – 0.291G+ 0.439B + 128
YCbCr[1] = (int)((-0.148 * red - 0.291 * green + 0.439 * blue) + 128);
//Cr = 0.439R – 0.368G – 0.071B + 128
YCbCr[2] = (int)((0.539 * red - 0.368 * green - 0.071 * blue) + 128);
return value
// index 0 holds values of Y 1 holds Cb values and 2 holds Cr vlaues
return YCbCr;
}
//Method to convert YCbCr block to RGB block
public static void YCrCbToRGB(int y[][], int Cb[][], int Cr[][]) {
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
//R = 1.164(Y – 16) + 1.596(Cr – 128)
red[i][j] = (int)(1.164 * (y[i][j] - 16) + (1.596 * (Cr[i][j] - 128)));
//G = 1.164(Y – 16) – 0.813(Cr – 128) – 0.391(Cb – 128)
green[i][j] = (int)(1.164 * (y[i][j] - 16) - (0.813 * (Cr[i][j] - 128)) - (0.391 * (Cb[i][j] - 128)));
//B = 1.164(Y – 16) + 2.018(Cb – 128)
blue[i][j] = (int)(1.164 * (y[i][j] - 16) + (2.018 * (Cb[i][j] - 128)));
}
}
}
上的随机行，表示像素数据发生了显着变化。以下是图像写入代码：
pixel block in Y space as input to DCT
223 224 226 227 229 229 230 230
226 227 227 227 228 229 229 230
228 228 228 228 228 229 230 231
228 228 228 228 229 231 233 234
227 228 229 230 231 233 234 234
226 227 229 230 232 233 233 233
227 228 230 232 232 231 229 228
228 230 232 234 232 229 226 223
示例输入和输出：
51 -1 0 0 0 0 0 0
-1 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
量化后和嵌入数据之前的DCT系数矩阵：
50 -1 0 1 0 0 0 0
-1 0 1 0 0 0 0 0
1 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
嵌入数据后的量化DCT系数：
232 227 223 223 227 231 232 231
230 226 222 223 226 230 230 229
228 224 221 222 226 229 229 227
226 223 221 223 227 229 228 225
226 224 223 225 229 230 228 225
227 225 225 228 232 233 230 226
228 227 228 231 235 236 232 228
230 229 230 234 237 238 233 229
在嵌入数据并应用IDCT后，像素在Y空间中阻塞：
#huge_it_portfolio_content_1 #huge_it_portfolio_container_1 {
max-width: 100%;
width: 88% !important;
opacity: 0;
margin: auto;
}
![input.jpg]](https://i.stack.imgur.com/njhxF.png)
![output.jpg]](https://i.stack.imgur.com/4uZz5.jpg)
我认为这是由于JPEG的有损性质所以我尝试了PNG但仍然遇到了同样的问题。
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