# High-Fidelity Steganography: A Covert Parity Bit Model-Based Approach
## 4 Proposed Scheme
### Data Embedding
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Coefficient**} & \multicolumn{3}{c}{**Proposed**} \\ \cline{3-8}  & & \multicolumn{3}{c}{**Replacement**} & \multicolumn{3}{c}{**Proposed**} \\ \hline
**Block Size** & **Capacity** & **Cover** & **PSNR** & **SSIM** & **PSNR** & **SSIM** & **Cost** \\ \hline \multirow{4}{*}{400 \(\times\) 400} & \multirow{4}{*}{14.65} & Airplane & 41.80 & 0.9856 & 44.87 & 0.9858 & 4.00\% \\ \cline{3-8}  & & Animal & 25.40 & 0.9945 & 30.53 & 0.9974 & 4.00\% \\ \cline{3-8}  & & Vegetables & 31.45 & 0.9947 & 39.01 & 0.9964 & 4.00\% \\ \hline \multirow{4}{*}{425 \(\times\) 425} & \multirow{4}{*}{16.54} & Airplane & 40.02 & 0.9845 & 43.72 & 0.9856 & 3.76\% \\ \cline{3-8}  & & Animal & 24.82 & 0.9926 & 29.05 & 0.9965 & 3.76\% \\ \cline{3-8}  & & Vegetables & 29.24 & 0.9926 & 36.60 & 0.9962 & 3.76\% \\ \hline \multirow{4}{*}{450 \(\times\) 450} & \multirow{4}{*}{18.54} & Airplane & 38.91 & 0.9672 & 42.41 & 0.9839 & 3.56\% \\ \cline{3-8}  & & Animal & 23.85 & 0.9895 & 26.99 & 0.9955 & 3.56\% \\ \cline{3-8}  & & Vegetables & 27.22 & 0.9878 & 33.67 & 0.9944 & 3.56\% \\ \hline \multirow{4}{*}{475 \(\times\) 475} & \multirow{4}{*}{20.66} & Airplane & 29.93 & 0.9628 & 38.64 & 0.9742 & 3.37\% \\ \cline{3-8}  & & Animal & 20.74 & 0.9820 & 23.45 & 0.9928 & 3.37\% \\ \cline{3-8}  & & Vegetables & 25.16 & 0.9744 & 31.10 & 0.9909 & 3.37\% \\ \hline \multirow{4}{*}{500 \(\times\) 500} & \multirow{4}{*}{22.89} & Airplane & 23.36 & 0.7913 & 32.91 & 0.9532 & 3.20\% \\ \cline{3-8}  & & Animal & 17.32 & 0.9539 & 19.34 & 0.9841 & 3.20\% \\ \cline{3-8}  & & Vegetables & 18.91 & 0.9560 & 24.86 & 0.9789 & 3.20\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of the proposed hiding scheme with the coefficient replacement idea in terms of the capacity–transparency trade-off. The capacity is measured using bpp, while the transparency is evaluated using the PSNR values [22] when \(n=15\). Table 3 shows the zigzag version described earlier in Section 4. The main advantage of the zigzag version is its reduced communication cost, as only one column needs to be modeled. Because there are only (\(n+1\)) coefficients to be sent to the receiver, the reduced communication cost does not significantly affect the performance of the proposed scheme. Based on Table 3, the zigzag version outperforms the coefficient replacement hiding strategy in all cases. Comparing the results between the column-by-column version and the zigzag version (Tables 2 and 3), it can be seen that the reduced communication cost does not significantly affect the performance of the hiding scheme; indeed, in certain cases hiding with the zigzag version shows improved results over the column-by-column version. For example, hiding in the \"Airplane\" cover image achieves a PSNR value of 45.09 dB with the zigzag version compared to 44.87 dB with the column-by-column version for the same hiding capacity ratio of 14.65 bpp. ### Comparison with Recent Schemes

Tables 4 and 5 show the best results achieved by the different steganography schemes in terms of the hiding capacity and stego quality. Tables 4 and 5 clearly prove the effectiveness of the proposed scheme, which outperforms recent steganography schemes in terms of both bpp and PSNR values. The only scheme to achieve a higher PSNR value was that of [PERSON] and Tsai [45], which achieved a PSNR value of 48.84 dB. However, this result was obtained with a very low hiding capacity ratio of 9.6 bpp, much lower than the capacity ratio achieved by the proposed scheme, which was 18.54 bpp for a competitive PSNR value of 42.41 dB.