## 3 Experiments and Analyses
### Image Quality Comparison  
To show the efficiency of the proposed method, the quality comparison of fused images is demonstrated. Four pairs of multi-focused images of a hot-air balloon, leopard, lab, and bottle are employed for quality comparison. It compares the quality of fused image based on visual effect, the accuracy of focused region detection, and the objective evaluations. The different images are used to show the differences between fused images and corresponding source images. This paper increases the contrast and brightness of difference images for printable purposes. All difference images are adjusted by using the same parameters. In the first comparison experiment, the \"hot-air balloon\" images are a pair of multi-focused images. The source multi-focused images are shown in Figure 4a,b. In Figure 4a, the biggest hot-air balloon on the bottom left is out of focus, the rest of the hot-air balloons are in focus. In contrast, in Figure 4b, the biggest hot-air balloon is in focus, but the rest of balloons are out of focus. LE, DWT, DT-CWT, CVT, NSCT, SR-DCT, SR-KSVD and the proposed method are employed to merge two multi-focused images into a clear one, respectively. The corresponding fusion results are shown in Figure 4c-j respectively. The difference images of LE, DWT, DT-CWT, CVT, NSCT, SR-DCT, SR-KSVD and the proposed method do the matrix subtraction with the source images shown in Figure 4a,b. The corresponding subtracted results are shown in Figure 5a-h,i-p respectively. Figure 5a-h are the difference images between Figure 4a and Figure 4c-j, and Figure 5i-p are the difference images between Figure 4b and Figure 4c-j. The difference images of LE, DWT, DT-CWT, CVT, NSCT, SR-DCT, SR-KSVD and the proposed method are the matrix subtraction results of the corresponding fused images and source images shown in Figure 4a,b. There are a lot of noises in Figure 4h, which are acquired by SR-DCT. The rest of integrated images in Figure 4 are similar. Difference images, that show hot-air balloons of LE, DWT, and DT-CWT on the left side respectively, do not get all the edge information in Figure 5a-c. Similarly, Figure 5i-k shows that the biggest hot-air balloons of LE, DWT, and DT-CWT on the bottom left, respectively, are not totally focused. Due to the misjudgement of focused areas, the fused \"hot-air balloon\" images of LE, DWT, DT-CWT, and SR-DCT have shortcomings. Compared with source images, the rest of the methods do great job in identifying the focused area. To further compare the quality of fused images, objective metrics are used. Table 1 shows the objective evaluations. Compared with the rest of the image fusion methods, the proposed method SR-SCC gets the largest value in MI and VIF. LE and DT-CWT get the largest value in EI and \(Q^{AB/F}\) respectively, but they provide an inaccurate decision in detecting the focused region. The proposed method has the best overall performance of multi-focus image fusion in the \"hot-air balloon\" scene among all eight methods, according to the quality of fused image, accuracy of locating focused region, and objective evaluations. Figure 4: Fused Images of “Hot-air Balloon” by Different Methods, (**a,b**) are source images, (**c**–j) are fused images of LE, DWT, DT-CWT, CVT, NSCT, SR-DCT, SR-KSVD, and proposed SR-SCC respectively. Figure 5: Difference Images of “Hot-air Balloon” by Different Methods, (**a**–**h**) are differences images between source image in Figure 4a and fused images of LE, DWT, DT-CWT, CVT, NSCT, SR-DCT, SR-KSVD, and proposed SR-SCC in Figure 4c–j respectively, (**i**–**p**) are differences images between source image in Figure 4b and corresponding fused images in Figure 4c–j respectively. Figure 8: Fused Images of “Bottle” by Different Methods, (**a**,**b**) are source images; (**c**–**j**) are fused images of LE, DWT, DT-CWT, CVT, NSCT, SR-DCT, SR-KSVD, and proposed SR-SCC respectively.