# A Topology Based Automatic Registration Method for Infrared and Polarized Coupled Imaging
## 3 Results and Discussion
### Real World Image Experiment  
The infrared image was taken by Bobcat-320-Star uncooled smart InGaAs camera from Xenics, the output resolution is 320 \(\times\) 256, and the spectral waveband is between 0.9-1.7 \(\upmu\)m. The polarization parameter image was taken by polarized microarray camera TRI050S-PC from Lucid Vision and the output resolution is 1224 \(\times\) 1024. The output of both cameras is in png format. We took 30 pairs of real-world images and some of them failed in all registration algorithms, as with other registration algorithms, SSR could not register a completely uniform scene. We took a fallen leaf on the lawn as an example scene to illustrate the comparative performance of each algorithm when a target appears in a uniform background. The polarization image is mainly composed of contours and textures. The veins on the leaves can be seen clearly from the image. By comparison, the infrared image is composed of gray level information, and near-infrared can image the lawn through the leaf. The data acquisition and processing flow are shown in Figure 6. This image pair can be found in [[https://drive.google.com/drive/folders/1](https://drive.google.com/drive/folders/1) zKAjsZole27 GT9 UHugWfQO6 Zm2 ULmYQ?usp=share_link]([https://drive.google.com/drive/folders/1](https://drive.google.com/drive/folders/1) zKAjsZole27 GT9 UHugWfQO6 Zm2 ULmYQ?usp=share_link), accessed on 11 October 2022. The registration accuracy rate of SSR reached 91.02% in the original image pair experiment. In contrast, SURF, MSER Brisk, FAST, Harris, and MinEigen did not work out the result due to the huge differences in features. It was unable for the nonlinear pixel value in  
Figure 5: A comparison of each algorithm, (**a**) Initial image pair; (**b**) Registered origin pair by SSR (**b1**) and registered segmented pair by SSR (**b2**); (**c**) Results of other algorithms, (**c1**) Mean Squares, (**c2**) Mattes MI, (**c3**) Phase-correlation, (**c4**) Powell and (**c5**) PSO. two images to derive gradient consistent regions for SURF and extreme value consistent regions for MSER. The complex texture of the lawn in the polarized parameter image could not provide available corner information for Brisk, FAST, MinEigen, and Harris. Infrared image and polarized parameter image share few common features. We segmented the region of interest in the image and test the feature-based algorithms again. However, the bright areas stray from the target of the infrared segmented image confusing them in getting the same features. Only SURF gave sufficient point pairs, but were mismatched. All rest algorithms tested in this experiment fail to register the segmented image pair. Table 2 shows the detected feature points of the algorithms, which were seldom matched either. The image segmentation helps SURF find out some match pairs, which are mismatched and helpless for achieving the correct registration. A state-of-the-art result of MIND is given in Figure 7, but it did not work. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Feature**} & \multicolumn{2}{c}{**Original Image Pair**} & \multicolumn{2}{c}{**Segmented Image Pair**} \\ \cline{2-5}  & **Detected Points** & **Matched Pairs** & **Detected Points** & **Matched Pairs** \\ \hline SURF & 0-55 & 0 & 80-366 & 13 \\ MSER & 14-122 & 0 & 2-6 & 0 \\ Brisk & 0-0 & 0 & 32-552 & 0 \\ FAST & 0-0 & 0 & 9-259 & 0 \\ Harris & 17-12 & 0 & 2-30 & 0 \\ MinEigen & 45-40 & 0 & 2-49 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Feature-based real world images registration experiment. Figure 6: SSR application in real world imaging. Figure 7: The real world image pair registered result by MIND. Compared with the registration algorithms BSO, GA, Powell, and PSO, based on the segmented image, the results are shown in the figure below, and the experimental result of manual registration is added. It can be read from Figure 8 that intensity-based algorithms in d, e, f, and g fail to register the infrared image and polarized parameter image.