## 4 Experimental Results
Figure 13a.2 is a stego-image, which is generated by embedding confidential data into a Lena image using the APD, APDLS(0), and ARDHA-(0) techniques. As explained on the next page, the APD, APDLS(0), and ARDHA-(0) techniques worked the same way. Therefore, as shown in Figure 13a.2, the stego-images generated by embedding confidential data in the cover image using APD, APDLS(0), and ARDHA-(0) techniques are identical. Figure 13b.2,c.2,d.2 are stego-images generated by embedding confidential data in blackb, Portofino, and ship using the APD, APDLS(0), and ARDHA-(0) techniques. Figure 13a.3-a.6 are stego-images generated by embedding confidential data into a Lena image using APDLS technique, where \(\beta\) is 5, 10, 15, and 20, respectively. Figure 13a.7-a.11 includes stego-images generated by embedding confidential data in Lena image using the ARDHA technique, where \(\beta\) is 0, 5, 10, 15, and 20, respectively. As shown in Figure 13, the visual quality of stego-image generated by applying ARDHA technique is very high. The cover image and the stego-image are visually identical. Thus, it is not possible to visually discern whether confidential data are embedded in the stego-image. Table 1 shows the quantitative values that measured the performance of the proposed technique via experimentation. Table 1 consists of two parts. The performance test results obtained by performing experiments on each of the techniques for calculating the seven predicted pixel values (i.e., V\({}_{1}\), V\({}_{2}\), V\({}_{3\rm V}\), V\({}_{3\rm C}\), V\({}_{4\rm S}\), V\({}_{4\rm N}\), and V\({}_{4\rm W}\)) used in the ARDHA technique are shown on the right side of the table. The overall performance test results of the ARDHA technique using all seven predicted pixel values are shown on the left side. The second to eighth columns of Table 1 show the overall results of experiments applying the ARDHA technique to embed confidential data in each cover image. The items of the experimental results from the second to eighth columns in Table 1 are number of hidden bits, PSNR (dB), prediction hit ratio (%), mean of prediction errors, number of predictions, and increase rate of hidden bits (%), respectively. Number of hidden bits represents the number of confidential data bits hidden in the cover image. PSNR (dB) is a measured value that represents the quality of a stego-image. Prediction hit ratio (%) is the number of accurate predictions divided by the total number of predictions, and subsequently multiplied by 100. Mean of the prediction errors represents the sum of the absolute values of the prediction errors divided by the total number of predictions. Number of predictions represents the total number of times the prediction was executed. Increase rate of hidden bits (%) represents the rate of increase in the number of hidden bits expressed as a percentage in the ARDHA and APDLS techniques compared to the APD technique. Compared with the APDLS technique, the increase rate of hidden bits in the ARDHA technique is shown in parentheses. The last seven columns in Table 1 contain the experimental results of the prediction hit ratio, the mean of prediction errors, and the number of predictions measured when predicting V\({}_{1}\), V\({}_{2}\), V\({}_{3\rm V}\), V\({}_{3\rm C}\), V\({}_{4\rm S}\), V\({}_{4\rm N}\), and V\({}_{4\rm W}\). P.H.R (%) represents the prediction hit ratio, M.P.E represents the mean of the prediction errors, and N. P represents the number of predictions.