# Visual Image Dehazing Using Polarimetric Atmospheric Light Estimation
## 4 Polarimetric Dark Channel Dehazing System  
### System Components and Workflow  
To achieve the real-time polarization dehazing of scenes, our engineers designed and manufactured a polarization dark channel dehazing system. The equipment we developed is a 150 mm aperture telescope system. Figure 5 shows the optical design and the photographs of the system.  
Our system consists of two detectors, including a black-and-white visible light polarization detector and a color visible light imaging detector. The polarization detector uses a CMOS sensor produced by Sony, specifically the IMX250 model. Compared to the imaging detector, this sensor offers higher detection capability and quantum efficiency. As a result, in our optical design, we split the incident light into polarization and imaging detectors in a ratio of 1:3 using a beamsplitter to ensure that the imaging detector receives a higher amount of incident light energy.  
To calculate the polarization degree of an image, four intensity images are required for the four polarization directions: 0\({}^{\circ}\), 45\({}^{\circ}\), 90\({}^{\circ}\), and 135\({}^{\circ}\). These four images need to be pixel-level registered. We manufactured the polarization detector using the Sony IMX250  
Figure 5: (**a**) Optical design of the system. (**b**) Appearance of the equipment. (**c**) Internal structure of the equipment.  
sensor, which is a pixel-level polarization sensor. Each pixel on the chip is equipped with a micro-polarizer in front. The detector has a resolution of \(2448\times 2048\). Each \(2\times 2\) pixel group contains polarization information in the four directions. Figure 6[23] shows the pixel arrangement of this detector. The camera's characteristics eliminate the need to find a suitable image registration algorithm to achieve pixel-level registration for the four images. In fact, on the IMX250 chip, each group that can be arranged in a \(2\times 2\) pattern contains energy from four polarization angles. Therefore, to preserve the original resolution as much as possible, we performed polarization state calculations on each group of four pixels in the \(2\times 2\) arrangement. This means that in the polarization state calculation process, each pixel, except for the edge pixels, is reused four times, corresponding to the four pixels in the final map of the degree of polarization (DOP). As a result, the final polarization image has a resolution of \(2447\times 2047\).  
Our color visible light camera has a resolution of \(2048\times 2048\) pixels. To achieve pixel-level alignment with the polarization camera, we used the ROI (region of interest) mode of the polarization camera for image acquisition. We set the ROI image center to be the center of the target surface and output images with the actual resolution of the color visible light camera. Through optical design, we ensured that the center pixels of both cameras overlap, thus obtaining images with the same field of view and resolution.  
Figure 7 shows the system workflow. During operation, the polarization detector is responsible for capturing polarization images and providing them to the polarization calculation module to generate polarization degree images. The acquisition detector receives a delayed trigger signal from the polarization detector, then exposes and captures color images. Subsequently, the polarization degree images and color images are passed to the dark channel dehazing module for haze removal processing. The final output is a color dehazed image.  
Figure 6: Distribution of the polarization detector’s pixels.  
Figure 7: Workflow of the system.