Finds the camera intrinsic and extrinsic parameters from several views of a calibration pattern

[cameraMatrix, distCoeffs, reprojErr] = cv.calibrateCamera(objectPoints, imagePts, imageSize)
[cameraMatrix, distCoeffs, reprojErr, rvecs, tvecs] = cv.calibrateCamera(...)
[...] = cv.calibrateCamera(..., 'OptionName', optionValue, ...)

Input

• objectPoints A cell array of cells of calibration pattern points in the calibration pattern coordinate space {{[x,y,z], ..}, ...}. The outer vector contains as many elements as the number of the pattern views. If the same calibration pattern is shown in each view and it is fully visible, all the vectors will be the same. Although, it is possible to use partially occluded patterns, or even different patterns in different views. Then, the vectors will be different. The points are 3D, but since they are in a pattern coordinate system, then, if the rig is planar, it may make sense to put the model to a XY coordinate plane so that Z-coordinate of each input object point is 0.
• imagePoints A cell array of cells of the projections of calibration pattern points {{[x,y], ..}, ...}. numel(imagePoints) and numel(objectPoints) must be equal, and numel(imagePoints{i}) must be equal to numel(objectPoints{i}) for each i.
• imageSize Size of the image used only to initialize the intrinsic camera matrix [w,h].

Output

• cameraMatrix Output 3x3 floating-point camera matrix A = [fx 0 cx; 0 fy cy; 0 0 1]
• distCoeffs Output vector of distortion coefficients [k1,k2,p1,p2,k3,k4,k5,k6,s1,s2,s3,s4,taux,tauy] of 4, 5, 8, 12 or 14 elements.
• reprojErr Output final re-projection error.
• rvecs Output cell array of rotation vectors (see cv.Rodrigues) estimated for each pattern view (cell array of 3-element vectors). That is, each k-th rotation vector together with the corresponding k-th translation vector (see the next output parameter description) brings the calibration pattern from the model coordinate space (in which object points are specified) to the world coordinate space, that is, a real position of the calibration pattern in the k-th pattern view (k=1:M)
• tvecs Output cell array of translation vectors estimated for each pattern view (cell array of 3-element vectors).

Options

• CameraMatrix Input 3x3 camera matrix used as initial value for cameraMatrix. If 'UseIntrinsicGuess' and/or 'FixAspectRatio' are specified, some or all of fx, fy, cx, cy must be initialized before calling the function. Not set by default (uses eye(3)).
• DistCoeffs Input 4, 5, 8, 12 or 14 elements vector used as an initial values of distCoeffs. Not set by default (uses zeros(1,14)).
• UseIntrinsicGuess Logical flag. When true, CameraMatrix contains valid initial values of fx, fy, cx, cy that are optimized further. Otherwise, (cx,cy) is initially set to the image center (imageSize is used), and focal distances are computed in a least-squares fashion. Note, that if intrinsic parameters are known, there is no need to use this function just to estimate extrinsic parameters. Use cv.solvePnP instead. default false.
• FixPrincipalPoint Logical flag. The principal point is not changed during the global optimization. It stays at the center or at a different location specified when 'UseIntrinsicGuess' is set too. default false.
• FixAspectRatio Logical flag. The functions considers only fy as a free parameter. The ratio fx/fy stays the same as in the input CameraMatrix. When 'UseIntrinsicGuess' is not set, the actual input values of fx and fy are ignored, only their ratio is computed and used further. default false.
• ZeroTangentDist Logical flag. Tangential distortion coefficients p1 and p2 are set to zeros and stay zero. default false.
• FixK1, ..., FixK6 Logical flag. The corresponding radial distortion coefficient is not changed during the optimization. If 'UseIntrinsicGuess' is set, the coefficient from the supplied DistCoeffs matrix is used. Otherwise, it is set to 0. default false.
• RationalModel Logical flag. Coefficients k4, k5, and k6 are enabled. To provide the backward compatibility, this extra flag should be explicitly specified to make the calibration function use the rational model and return 8 coefficients. If the flag is not set, the function computes and returns only 5 distortion coefficients. default false.
• ThinPrismModel Logical flag. Coefficients s1, s2, s3 and s4 are enabled. To provide the backward compatibility, this extra flag should be explicitly specified to make the calibration function use the thin prism model and return 12 coefficients. If the flag is not set, the function computes and returns only 5 distortion coefficients. default false.
• FixS1S2S3S4 Logical flag. The thin prism distortion coefficients are not changed during the optimization. If 'UseIntrinsicGuess' is set, the coefficient from the supplied DistCoeffs matrix is used. Otherwise, it is set to 0. default false.
• TiltedModel Coefficients tauX and tauY are enabled. To provide the backward compatibility, this extra flag should be explicitly specified to make the calibration function use the tilted sensor model and return 14 coefficients. If the flag is not set, the function computes and returns only 5 distortion coefficients. default false.
• FixTauXTauY The coefficients of the tilted sensor model are not changed during the optimization. If UseIntrinsicGuess is set, the coefficient from the supplied DistCoeffs matrix is used. Otherwise, it is set to 0. default false.
• UseLU Use LU instead of SVD decomposition for solving. Much faster but potentially less precise. default false.
• Criteria Termination criteria for the iterative optimization algorithm. default struct('type','Count+EPS', 'maxCount',30, 'epsilon',eps)

The function estimates the intrinsic camera parameters and extrinsic parameters for each of the views. The algorithm is based on [Zhang2000] and [BoughuetMCT]. The coordinates of 3D object points and their corresponding 2D projections in each view must be specified. That may be achieved by using an object with a known geometry and easily detectable feature points. Such an object is called a calibration rig or calibration pattern, and OpenCV has built-in support for a chessboard as a calibration rig (see cv.findChessboardCorners). Currently, initialization of intrinsic parameters (when 'UseIntrinsicGuess' is not set) is only implemented for planar calibration patterns (where Z-coordinates of the object points must be all zeros). 3D calibration rigs can also be used as long as initial CameraMatrix is provided.

The algorithm performs the following steps:

1. Compute the initial intrinsic parameters (the option only available for planar calibration patterns) or read them from the input parameters. The distortion coefficients are all set to zeros initially unless some of 'FixK?' are specified.
2. Estimate the initial camera pose as if the intrinsic parameters have been already known. This is done using cv.solvePnP.
3. Run the global Levenberg-Marquardt optimization algorithm to minimize the reprojection error, that is, the total sum of squared distances between the observed feature points imagePoints and the projected (using the current estimates for camera parameters and the poses) object points objectPoints. See cv.projectPoints for details.

Note

If you use a non-square (=non-NxN) grid and cv.findChessboardCorners for calibration, and cv.calibrateCamera returns bad values (zero distortion coefficients, an image center very far from (w/2-0.5,h/2-0.5), and/or large differences between fx and fy (ratios of 10:1 or more), then you have probably used patternSize=[rows,cols] instead of using patternSize=[cols,rows] in cv.findChessboardCorners.

References

[Zhang2000]:

Zhengyou Zhang. "A flexible new technique for camera calibration". Pattern Analysis and Machine Intelligence, IEEE Transactions on, 22(11):1330-1334, 2000.

[BoughuetMCT]:

Jean-Yves Bouguet. "Camera calibration toolbox for matlab" [eb/ol], 2004.