# Calibration of fisheye camera using entrance pupil

## TL;DR

This paper introduces a calibration method for fisheye cameras that accounts for entrance pupil variations to improve intrinsic parameter accuracy, using a new model and optimization techniques.

## Contribution

It proposes a novel formation model that relaxes the single viewpoint assumption for fisheye lenses by modeling the entrance pupil, enhancing calibration accuracy.

## Key findings

- Achieved slightly better re-projection error than traditional methods
- Obtained more accurate camera parameters
- Calibration procedure is simple and adaptable

## Abstract

Most conventional camera calibration algorithms assume that the imaging device has a Single Viewpoint (SVP). This is not necessarily true for special imaging device such as fisheye lenses. As a consequence, the intrinsic camera calibration result is not always reliable. In this paper, we propose a new formation model that tends to relax this assumption so that a Non-Single Viewpoint (NSVP) system is corrected to always maintain a SVP, by taking into account the variation of the Entrance Pupil (EP) using thin lens modeling. In addition, we present a calibration procedure for the image formation to estimate these EP parameters using non linear optimization procedure with bundle adjustment. From experiments, we are able to obtain slightly better re-projection error than traditional methods, and the camera parameters are better estimated. The proposed calibration procedure is simple and can easily be integrated to any other thin lens image formation model.