Model and calibration of underwater stereo vision based on the light field

Abstract

In an underwater imaging system, a refractive interface is introduced when a camera looks into the water-based environment, resulting in the usually linear rays of light bending and the commonly used pinhole camera model to be invalid. In this paper, a novel method to model and calibrate the underwater stereo system is proposed. Unlike most existing recent works that use vector operations to express light propagation, this paper remodels the underwater imaging system in the view of the light field, which is more organized and concise. Additionally, a forward projection error function, which is more accurate and efficient, is used for non-linear optimization to minimize the reprojection error. The proposed method allows improved accuracy compared with other methods and is evaluated in a set of experiments.

Forward projection multilayer refraction model for underwater camera calibration

“…As previously mentioned, for multiple sets of underwater camera calibration experiments conducted by nine cameras, the calibration identification results by our proposed refraction method are more stable (within 5.4%) than the calibration identification results by Agrawal's refraction model 20 (within 7.6%) and Zhang's refraction model 22 (within 12.2%).…”

“…It is worth noting that Li's refraction model 17 is unable to identify the above parameters. Using Agrawal's refraction model, 20 Zhang's refraction model, 22 and our refraction model, respectively, the above identified parameters are solved and listed in Table 2. Parameters 20 our refraction model has nearly the same reprojection error, shorter computation time, higher identification precision (e.g., d m , n 1 , and n 2 ), and more identification parameter (e.g., f).…”

“…Due to the complexity of the underwater environment, many scholars have carried out relevant research on how to weaken or eliminate the influence of the underwater environment on the measurement accuracy, which can be mainly divided into three categories: pinhole imaging method, 12 equivalent compensation method, 13 – 17 and theory compensation method 18 – 22 The pinhole imaging method is to directly apply the pinhole model in underwater imaging for camera calibration and corresponding reconstruction without considering the particularity of underwater imaging. The equivalent compensation method is to equate the effect brought by underwater refraction with the radial distortions of the lens or the change of the camera focal length.…”

“…Wu and Tang 21 proposed a binocular stereo underwater measurement method based on the physical process of underwater imaging, which is only for single-time refraction and has a limited scope of application due to its relatively simple model. Based on the light field, Zhang et al 22 . presented a backward projection method to model and calibrate the underwater stereo system, which has simple experimental validation, poor measurement robustness, and low measurement accuracy without convincing accuracy verification experiment.…”

Direct Estimation of the Relative Orientation in Underwater Environment

“…Furthermore, the model exhibited sensitivity to noise, especially when using thin glass interface or when the distance between the perspective center and the interface was small. A pose and calibration models for an underwater stereo imaging system was proposed by Zhang et al (2018) where the authors remodeled the underwater imaging system in the view of the light filed parametrization and proposed a forward projection error function which was minimized in a non-linear optimization fashion. The literature shows that because of refraction, underwater imaging suffers from depth-dependent, non-linear distortions and that the imaging system does not follow the standard SVP model.…”