Light field geometry of a standard plenoptic camera

Abstract

The Standard Plenoptic Camera (SPC) is an innovation in photography, allowing for acquiring two-dimensional images focused at different depths, from a single exposure. Contrary to conventional cameras, the SPC consists of a micro lens array and a main lens projecting virtual lenses into object space. For the first time, the present research provides an approach to estimate the distance and depth of refocused images extracted from captures obtained by an SPC. Furthermore, estimates for the position and baseline of virtual lenses which correspond to an equivalent camera array are derived. On the basis of paraxial approximation, a ray tracing model employing linear equations has been developed and implemented using Matlab. The optics simulation tool Zemax is utilized for validation purposes. By designing a realistic SPC, experiments demonstrate that a predicted image refocusing distance at 3.5 m deviates by less than 11% from the simulation in Zemax, whereas baseline estimations indicate no significant difference. Applying the proposed methodology will enable an alternative to the traditional depth map acquisition by disparity analysis.

Refocusing distance of a standard plenoptic camera

“…It is of particular importance to detect MICs correctly since they are taken as reference origins in the image synthesis process. Contrary to previous approaches [11,12], all chief rays impinging on the MIC positions originate from the exit pupil center which, for simplicity, coincides with the main lens optical center in Fig. 2.…”

“…In our previous model [11], it is assumed that each MIC lies on the optical axis of its corresponding micro lens. It was mentioned that this hypothesis would only be true where the main lens is at an infinite distance from the MLA [14].…”

“…In previous studies [11,12], the refocusing distance has been found by geometrically tracing light rays through the lenses and finding their intersection in object space. Alternatively, rays can be seen as intersecting behind the sensor which is illustrated in Fig.…”

“…While the SPC has made its way to the consumer photography market, our research group proposed ray models aiming to estimate distances which have been computationally brought to focus [11,12]. These articles laid the groundwork for estimating the refocusing distance by regarding specific light rays as a system of linear functions.…”

“…The experimental results supplied in recent work showed matching estimates for far distances, but incorrect approximations for objects close to the SPC [12]. A benchmark comparison of the previous distance estimator [11] with a real ray simulation software [13] has revealed errors of up to 11 %. This was due to an approach inaccurate at locating micro image center positions.…”