## 3 The Proposed Method  
In this section, we will present the proposed LSB-based steganography method that aimed at enhancing embedding capacity, achieving good visual quality, and security against steganalysis detection attacks. The proposed method extends the concept of LSB substitution. This employed the mapping of secret data bits with cover pixel bits, where the record of mapping is maintained by the LSB substitution in cover pixels. For data security, the proposed method also applies the permutation on secret data bits using a shared key. In the embedding process, first, the secret data bits are grouped into two secret bits pairs, i.e., \(M_{1}(10)\), \(M_{2}(10)\), \(M_{3}(11)\),... as shown in Figure 1a. Similarly, all the cover pixels bits are also categorized as pairs, i.e., Left Pair (\(C_{\text{L,pixel}}\)) and Right Pair (\(C_{\text{R,pixel}}\)) depicted in Figure 1b. \(C_{\text{L,pixel}}\) denotes the 7 th and 8 th MSBs of the cover pixel, and similarly, \(C_{\text{R,pixel}}\) denotes the 5 th and 6 th MSBs \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Approaches**} & **Embedding** & **Visual Quality** & **Undetectability** & \multirow{2}{*}{**Maximum Used LSBs/byte**} \\  & **Capacity (bpp)** & **(PSNR)** & **Security** & \\ \hline [PERSON] et al. 2014 [8] & 3.16 & 33.40 & - & 4 bits LSB \\ \hline [PERSON] and [PERSON] 2015 [9] & 2.55 & 37.56 & - & 3 bits LSB \\ \hline [PERSON] and [PERSON] 2016 [10] & 3.19 & 38.87 & - & 4 bits LSB \\ \hline [PERSON] et al. 2016 [13] & 3.17 & 39.29 & RS analysis & 3 bits LSB \\ \hline [PERSON] et al. 2016 [15] & 3.13 & 38.42 & - & 4 bits LSB \\ \hline [PERSON] et al. 2018 [14] & 3.11 & 38.40 & RS analysis & 3 bits LSB \\ \hline [PERSON] et al. 2018 [17] & 4.05 & 30.10 & - & 1–5 bits LSB \\ \hline [PERSON] et al. 2018 [18] & 2.83 & 43.7 & - & All 4 bits LSB or Two 3 bits \\ \hline Wien. 2018 [22] & -1.0 & 32.27 & - & 1 bits \\ \hline [PERSON] and [PERSON]. 2018 [23] & 1.13 & 47.83 & - & 1 bits + 2 bits + 3 bits RGB LSB \\ \hline \hline \end{tabular}
\end{table} 
Table 1: General performance comparison of existing methods, PSNR: peak signal to noise ratio. of the cover pixel. Both \(C_{\text{L,pixel}}\) and \(C_{\text{R,pixel}}\) bits would be used for mapping with secret data bits pair. In the same way, the 1 st and 2 nd LSBs of cover pixel also denoted with Right Bit (\(B_{\text{R,pixel}}\)) and Left Bit (\(B_{\text{L,pixel}}\)) and used as an indicator for mapping of pixels pair. \(B_{\text{L,pixel}}\) and \(B_{\text{R,pixel}}\) are closely coupled with \(C_{\text{L,pixel}}\) and \(C_{\text{R,pixel}}\) in terms of indicator bits, respectively. However, the mapping strategies consist of the following cases. 1. If first secret bit pair (i.e., \(M_{1}\)) is matched with the \(C_{\text{L,pixel}}\) of a cover pixel then \(B_{\text{L,pixel}}\) is replaced with '1' otherwise replaced it with '0'. 2. Similarly, if the second secret bit pair (i.e., \(M_{2}\)) is matched with \(C_{\text{R,pixel}}\), it substitutes \(B_{\text{R,pixel}}\) with '1' otherwise replaces it with '0'. 3. If either \(B_{\text{L,pixel}}\) or \(B_{\text{R,pixel}}\) is '0', then the 2-LSBs of very next cover pixel would be replaced with the previous unmatched secret bit pair (i.e., \(M_{1}\) or \(M_{2}\)). 4. If both \(B_{\text{L,pixel}}\) and \(B_{\text{R,pixel}}\) are '0', it would indicate the skipped mapped block (which does not contain any mapping). For example, from Figure 1, the first pixel of cover image has the following values, \(C_{\text{L,1}}=01\), \(C_{\text{R,1}}=10\), \(B_{\text{L,1}}=1\), \(B_{\text{R,1}}=0\) and the secret bits pair are \(M_{1}=10\), \(M_{2}=10\). From case 1, \(C_{\text{L,1}}\
eq M_{1}\), i.e., \(01\
eq 10\), so it replaces the (\(B_{\text{L,1}}\)) 1 with 0. Similarly, from case 2, \(C_{\text{R,1}}=M_{2}\), so it substitutes the 1 in \(B_{\text{R,1}}\) location. Next, the case 3 conditioned would be satisfied, i.e., if \(B_{\text{L,1}}=0\) or \(B_{\text{R,1}}=0\), then embed the remaining unmatched secret pair that was \(M_{1}=10\).