Research on Information Hiding Technology Based on Color Digital Still Images(4)

3.3. Image Data In the 24-bit format, each pixel in the image is represented by a three-byte RGB sequence. Each scan line is complemented to 4 bits. The image is stored bottom-up, ie the first scan line is the last scan line in the image. The following figure shows the bitmap file's header (BITMAPHEADER) and bitmap information header (BITMAPINFOHEADER) and part of the image data:

Figure 3.1 Local Example Bitmap File

4. Information hiding algorithm based on color digital still images After analyzing the basic framework of the information hiding algorithm and the BMP file format of color images, this paper proposes an information hiding algorithm based on color still digital images, as shown in Figure 4.1 and This is shown in Figure 4.2.

Algorithm 4.1 (Information hiding embedded algorithm based on color digital still images)

Write the byte length of the information to be hidden (hereinafter referred to as the signature signal) in the reserved byte of the header part of the BMP file;
Convert the signature signal into a binary data stream;
The upper 7 bits of each byte of the image data portion of the BMP file are sequentially exclusive ORed and then the result of the exclusive OR of the above binary digital stream is written into the lowest bit;

Figure 4.1 Information hiding embedded process based on color digital still images

Algorithm 4.2 (Information hiding and extraction algorithm based on color still digital images)

Read the reserved byte value of the header part of the BMP file and set it to L. If 0, there is no hidden information and the algorithm is terminated. If it is not 0, the value is the byte length of the hidden information.
Eight bits of each byte of the image data portion of the BMP file are in turn exclusive-ORed, and the result thereof is saved;
Repeat step (2) so that every 8 BMP file image data bytes are processed to form a hidden information byte;
Repeat (2), (3) until the length of the hidden information byte is L.

Figure 4.2 The information hiding extraction process based on color still digital images can prove that the extracted information is the embedded signature signal. Taking a bit S of the signature signal as an example, a corresponding bitmap data byte is X7X6X5X4X3X2X1X0, and the bitmap data byte after the embedded signature signal is X7X6X5X4X3X2X1X0`, where:
X0` = X7⊕X6⊕X5⊕X4⊕X3⊕X2⊕X1⊕S

Let the extracted signature signal be S`, then,
S` =X7⊕X6⊕X5⊕X4⊕X3⊕X2⊕X1⊕X0`
= (X7⊕X6⊕X5⊕X4⊕X3⊕X2⊕X1⊕X7)⊕ (X6⊕X5⊕X4⊕X3⊕X2⊕X1⊕S)
= (X7⊕X6⊕X5⊕X4⊕X3⊕X2⊕X1⊕X7)⊕ (X6⊕X5⊕X4⊕X3⊕X2⊕X1)⊕S
=S

Completion.

Figure 4.3 Original Lena image