Camera auto-calibration is the process of determining internal camera

Pinhole camera model

The pinhole camera model describes the mathematical relationship between the coordinates of a 3D point and its projection onto the image plane of an ideal pinhole camera, where the camera aperture is described as a point and no lenses are used to focus light...

 parameters directly from multiple uncalibrated images. In contrast to classic camera calibration

Camera resectioning

Camera resectioning is the process of finding the true parameters of the camera that produced a given photograph or video. Usually, the camera parameters are represented in a 3 × 4 matrix called the camera matrix....

, auto-calibration does not require any special calibration objects in the scene.

Problem statement

Given set of cameras and 3D points reconstructed up to projective ambiguity (using, for example, bundle adjustment

Bundle adjustment

Given a set of images depicting a number of 3D points from different viewpoints, bundle adjustment can be defined as the problem of simultaneously refining the 3D coordinates describing the scene geometry as well as the parameters of the relative motion and the optical characteristics of the camera...

 method) we wish to define rectifying homography such that is a metric reconstruction. After that internal camera parameters can be easily calculated using camera matrix

Camera matrix

In computer vision a camera matrix or projection matrix is a 3 \times 4 matrix which describes the mapping of a pinhole camera from 3D points in the world to 2D points in an image....

 factorization .

Algorithms of camera auto-calibration

• Using the Kruppa equations. Historically the first auto-calibration algorithms. It bases on the correspondence of epipolar lines tangent to the absolute conic on the plane at infinity.
• Using the absolute dual quadratic.
• The modulus constraint.