Investigation Into the Behaviour and Modelling of Chromatic Aberrations in Non-Metric Digital Cameras

Abstract

Abstract. Chromatic aberration in colour digital camera imagery can affect the accuracy of photogrammetric reconstruction. Both longitudinal and transverse chromatic aberrations can be effectively modelled by making separate measurements in each of the blue, green and red colour bands and performing a specialized self-calibrating bundle adjustment. This paper presents the results of an investigation with two aims. The first aim is to quantify the presence of chromatic aberration in two sets of cameras: the six individual cameras comprising a Ladybug5 system, calibrated simultaneously in air; and four GoPro Hero 5 cameras calibrated independently under water. The second aim is to investigate the impacts of imposing different constraints in the self-calibration adjustment. To this end, four different adjustment cases were performed for all ten cameras: independent adjustment of the observations from each colour band; combined adjustment of all colour bands’ observations with common object points; combined adjustment of all colour bands with common object points and common exterior orientation parameters for each colour band triplet; and combined adjustment with common object points and certain common interior orientation parameters. The results show that the Ladybug5 cameras exhibit a small (1-2 pixel) amount of transverse chromatic aberration but no longitudinal chromatic aberration. The GoPro Hero 5 cameras exhibit significant (25 pixel) transverse chromatic aberration as well as longitudinal chromatic aberration. The principal distance was essentially independent of the adjustment case for the Ladybug5, but it was not for the GoPro Hero 5. The principal point position and precision were both affected considerably by adjustment case. Radial lens distortion was invariant to the adjustment case. The impact of adjustment case on decentring distortion was minimal in both cases.

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

“…The final adjustment used the constraint of the second adjustment as well as the constraints to enforce the equivalence of the principal point coordinates of the cameras corresponding to the three spectral bands. The third adjustment used by [26] is comparable to the adjustment used by [25,26], who concluded that ether common object points or alternatively, common object points with EOP constraints are needed.…”

“…In this paper, a similar method to [25,26] is used. In this section, the functional model and the add adjustment constraints will be introduced.…”

“…One approach for modelling CA is based on the self-calibrating bundle adjustment [25]. In [26], the self-calibration approach is investigated using a bundle adjustment for cameras of a Ladybug system in-air as well as several GoPro cameras underwater. In contrast to previous works, the application of different constraints was specifically investigated.…”

“…The cameras were not stopped or paused when moving from the underwater calibration field to the in-air calibration field, aiming to keep the relative positions of the cameras to each other constant. Unfortunately, the frame mount was not as rigid as required for constraining the relative orientation stability of the cameras [26].…”

“…For the underwater images, the cameras mounted in the frame were submerged in a freshwater tank containing a target array. The calibration frame comprising 133 white targets (5 mm diameter) on a black background and is identically with the underwater calibration frame used by [26] (Figure 3, left). The distance between the camera stations and the frame was approximately 1.5 m. The field of view of the camera is reduced considerably underwater due to the introduction of the planar port.…”