US 9,438,897 B2 · Method and apparatus for automatic camera calibration using one or more images of a checkerboard pattern

Abstract

The present invention relates to a high precision method, model and apparatus for calibrating, determining the rotation of the lens scope around its symmetry axis, updating the projection model accordingly, and correcting the image radial distortion in real-time using parallel processing for best image quality. The solution provided herein relies on a complete geometric calibration of optical devices, such as cameras commonly used in medicine and in industry in general, and subsequent rendering of perspective correct image in real-time. The calibration consists on the determination of the parameters of a suitable mapping function that assigns each pixel to the 3D direction of the corresponding incident light. The practical implementation of such solution is very straightforward, requiring the camera to capture only a single view of a readily available calibration target, that may be assembled inside a specially designed calibration apparatus, and a computer implemented processing pipeline that runs in real time using the parallel execution capabilities of the computational platform.

Claims16

Dependent claims

An apparatus for camera calibration comprising the following:

(i) a calibration box (1) made of opaque materials for avoiding the entrance of light from the exterior, and having one or more openings (2) for allowing access to a lens probe, each opening being surrounded by a rubber membrane (3) that minimizes the entrance of light from the exterior;
the box is divided in two compartments by a separator (6) in transparent or translucent material, an open compartment that can be filled with a fluid for replicating the means where the visual inspection will be carried;
(ii) a planar grid (7) with a known pattern, made of transparent or translucent material, which is placed on the top of the separator;
(iii) a light source, installed in the lower box compartment (5), for diffuse back-illumination of the planar grid;
(iv) a computer unit, with sequential and parallel processing capabilities, comprising a Central Processing Unit and/or a Graphics Processing Unit, that is connected to a camera for image acquisition of a single image of the known pattern;
the acquired image used as an input to perform camera calibration;
(v) a display device connected to the computer unit;
(vi) and an interface device connected to the computer unit for entering user commands.

5 more elements

A method for automatic camera calibration such as in medical or industrial devices like endoscopic cameras, a projection model updating according to the lens probe rotation, and a real-time image distortion correction that carries out the following operations:

(i) user command acquisition of one or more calibration images of a checkerboard pattern using a calibration box;
(ii) detection of the grid corners in the calibration images and establishment of image-plane correspondences;
(iii) determination of a camera's intrinsic parameters such as focal length, principal point, skew and aspect ratio and the lens distortion, using the image-plane correspondences in at least one of the calibration images;
(iv) continuous image/video acquisition;
(v) detection, when applicable, of a boundary contour between circular and frame image regions, and image coordinates of a triangular mark, this operation being carried out at each frame time instant;
(vi) robust determination, when applicable, of an angular displacement undergone by a lens probe with respect to camera head using output of (v);
(vii) updating intrinsic calibration information given an initial camera calibration of (iii) and, when applicable, a relative rotation information of (vi), making use of a new projection model for describing oblique viewing endoscopes or other camera device where a lens probe rotates with respect to a camera-head;
and
(viii) performing real-time image rectification for correction of radial distortion using the current camera calibration of (vii).

6 more elements

Dependencies are inferred from the claim text.

Method and apparatus for automatic camera calibration using one or more images of a checkerboard pattern

Life of this patent

Method and apparatus for automatic camera calibration using one or more images of a checkerboard pattern

Life of this patent

Abstract

Claims16