Investigation of Chromatic Aberration and Its Influence on the Processing of Underwater Imagery

Abstract

The number of researchers utilising imagery for the 3D reconstruction of underwater natural (e.g., reefs) and man-made structures (e.g., shipwrecks) is increasing. Often, the same procedures and software solutions are used for processing the images as in-air without considering additional aberrations that can be caused by the change of the medium from air to water. For instance, several publications mention the presence of chromatic aberration (CA). The aim of this paper is to investigate CA effects in low-cost camera systems (several GoPro cameras) operated in an underwater environment. We found that underwater and in-air distortion profiles differed by more than 1000 times in terms of maximum displacement and in terms of curvature. Moreover, significant CA effects were found in the underwater profiles that did not exist in-air. Furthermore, the paper investigates the effect of adjustment constraints imposed on the underwater self-calibration and the reliability of the interior orientation parameters. The analysis of the precision shows that in-air RMS values are just due to random errors. In contrast, the underwater calibration RMS values are 3x-6x higher than the exterior orientation parameter (EOP) precision, so these values contain both random error and the systematic effects from the CA. The accuracy assessment shows significant differences.

Good Vibrations? How Image Stabilisation Influences Photogrammetry

“…For example, Menna et al (2017) analysed the accuracy potential lost in underwater photogrammetry due to optical aberrations introduced by the underwater port. Chromatic aberrations have been addressed for high precision photogrammetry (Luhmann et al, 2006) and in underwater photogrammetry as well (Neyer et al, 2019;Helmholz and Lichti, 2020). An automatic detection and removal approach of blurred UAV images was developed by Sieberth et al (2016) to improve analysis and interpretation of the data, as well as the accuracy of the photogrammetric processing.…”

Modelling extreme wide‐angle lens cameras

“…This is perhaps natural due to the high degree of barrel distortion found in EWA imagery that is associated with the fisheye effect. Large radial lens distortion, in excess of 100 % of the distance between principal point and image format corner, has been reported for EWA cameras (Helmholz and Lichti, 2020; Lichti et al., 2020). However, as pointed out by Miyamoto (1964), a fisheye lens is not “an extension of a wide‐angle lens”.…”

“…A selection of action cameras, panoramic systems and mobile phones are examined. In recent years, a number of authors have reported on the calibration of action cameras – GoPro cameras in particular – due to their increased ubiquity, compact and lightweight design as well as robustness (Balletti et al., 2014; Ballarin et al., 2015; Teo, 2015; Hastedt et al., 2016; Bernardina et al., 2017; Wierzbicki, 2018b; Helmholz and Lichti, 2020). Similarly, panoramic camera systems featuring multiple, integrated sensors have also received attention in terms of the geometric calibration, notably Ladybug systems (Bosch et al., 2015; Rau et al., 2016; Lichti et al., 2020) and the Panono system (Khoramshahi and Honkavaara, 2018).…”

“…The successful use of the central perspective model with a five‐term radial lens distortion curve for EWA systems has been demonstrated for GoPro cameras (Helmholz and Lichti, 2020) and the Ladybug system (Lichti et al., 2020). As shown in the latter work, inclusion of the extra terms was needed to completely describe the barrel distortion and to maximise 3D reconstruction accuracy.…”

Editorial for Underwater 3D Recording & Modelling

“…As authors report in [8], underwater chromatic aberration is more dominant in the underwater environment, and therefore significantly affects accuracy. Experiments using low-cost cameras, in water and in air show that accuracy varies considerably.…”