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cameraParameters class

Object for storing camera parameters

Description

This object contains the intrinsic, extrinsic, and lens distortion parameters of a camera.

Syntax

cameraParams = cameraParameters
cameraParams = cameraParameters(Name,Value)

Construction

cameraParams = cameraParameters returns an object that contains the intrinsic, extrinsic, and lens distortion parameters of a camera.

cameraParams = cameraParameters(Name,Value) configures the camera parameters object properties, specified as one or more Name,Value pair arguments. Unspecified properties use default values.

Input Arguments

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The object contains intrinsic, extrinsic, lens distortion, and estimation properties.

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside single quotes (' '). You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'RadialDistortion',[0 0 0] sets the 'RadialDistortion' to [0 0 0].

'IntrinsicMatrix' — Projection matrix3-by-3 identity matrix

Projection matrix, specified as the comma-separated pair consisting of 'IntrinsicMatrix' and a 3-by-3 identity matrix. For the matrix format, the object uses the following format:

The coordinates [cx cy] represent the optical center (the principal point), in pixels. When the x and y axis are exactly perpendicular, the skew parameter, s, equals 0.

fx = F*sx
fy = F*sy
F, is the focal length in world units, typically expressed in millimeters.
[sx, sy] are the number of pixels per world unit in the x and y direction respectively.
fx and fy are expressed in pixels.

'RadialDistortion' — Radial distortion coefficients[0 0 0] (default) | 2-element vector | 3-element vector

Radial distortion coefficients, specified as the comma-separated pair consisting of 'RadialDistortion' and either a 2- or 3-element vector. If you specify a 2-element vector, the object sets the third element to 0.

Radial distortion occurs when light rays bend more near the edges of a lens than they do at its optical center. The smaller the lens, the greater the distortion.

The camera parameters object calculates the radial distorted location of a point. You can denote the distorted points as (xdistorted, ydistorted), as follows:

xdistorted = x(1 + k1*r2 + k2*r4 + k3*r6)

ydistorted= y(1 + k1*r2 + k2*r4 + k3*r6)

x, y = undistorted pixel locations
k1, k2, and k3 = radial distortion coefficients of the lens
r2 = x2 + y2

Typically, two coefficients are sufficient. For severe distortion, you can include k3. The undistorted pixel locations appear in normalized image coordinates, with the origin at the optical center. The coordinates are expressed in world units.

'TangentialDistortion' — Tangential distortion coefficients[0 0]' (default) | 2-element vector

Tangential distortion coefficients, specified as the comma-separated pair consisting of 'TangentialDistortion' and a 2-element vector. Tangential distortion occurs when the lens and the image plane are not parallel.

The camera parameters object calculates the tangential distorted location of a point. You can denote the distorted points as (xdistorted, ydistorted), as follows:

xdistorted = x + [2 * p1 * x * y + p2 * (r2 + 2 * x2)]

ydistorted = y + [p1 * (r2 + 2*y2) + 2 * p2 * x * y]

x, y = undistorted pixel locations
p1 and p2 = tangential distortion coefficients of the lens
r2 = x2 + y2

The undistorted pixel locations appear in normalized image coordinates, with the origin at the optical center. The coordinates are expressed in world units.

'RotationVectors' — Camera rotationsM-by-3 matrix | []

Camera rotations, specified as the comma-separated pair consisting of 'RotationVectors' and an M-by-3 matrix. The matrix contains rotation vectors for M images, which contain the calibration pattern that estimates the calibration parameters. Each row of the matrix contains a vector that describes the 3-D rotation of the camera relative to the corresponding pattern.

Each vector specifies the 3-D axis about which the camera is rotated. The magnitude of the vector represents the angle of rotation in medians. You can convert any rotation vector to a 3-by-3 rotation matrix using the Rodrigues formula.

You must set the RotationVectors and TranslationVectors properties together in the constructor to ensure that the number of rotation vectors equals the number of translation vectors. Setting only one property but not the other results in an error.

'TranslationVectors' — Camera translationsM-by-3 matrix | []

Camera translations, specified as the comma-separated pair consisting of 'RotationVectors' and an M-by-3 matrix. This matrix contains translation vectors for M images. The vectors contain the calibration pattern that estimates the calibration parameters. Each row of the matrix contains a vector that describes the translation of the camera relative to the corresponding pattern, expressed in world units.

The following equation provides the transformation that relates a world coordinate [X Y Z] and the corresponding image point [x y]:

R is the 3-D rotation matrix.
t is the translation vector.
K is the IntrinsicMatrix.
s is a scalar.

This equation does not take distortion into consideration. Distortion is removed by the undistortImage function.

You must set the RotationVectors and TranslationVectors properties together in the constructor to ensure that the number of rotation vectors equals the number of translation vectors. Setting only one property results in an error.

'WorldPoints' — World coordinatesM-by-2 array | []

World coordinates of key points on calibration pattern, specified as the comma-separated pair consisting of 'WorldPoints' and an M-by-2 array. M represents the number of key points in the pattern.

'WorldUnits' — World points units'mm' (default) | string

World points units, specified as the comma-separated pair consisting of 'WorldUnits' and a string. The string describes the units of measure.

'EstimateSkew' — Estimate skew flagfalse (default) | logical scalar

Estimate skew flag, specified as the comma-separated pair consisting of 'EstimateSkew' and a logical scalar. When you set the logical to true, the object estimates the image axes skew. When you set the logical to false, the image axes are exactly perpendicular.

'NumRadialDistortionCoefficients' — Number of radial distortion coefficients2 (default) | 3

Number of radial distortion coefficients, specified as the comma-separated pair consisting of 'NumRadialDistortionCoefficients' and the number '2' or '3'.

'NumRadialDistortionCoefficients' — Number of radial distortion coefficients2 (default) | 3

Number of radial distortion coefficients, specified as the comma-separated pair consisting of 'NumRadialDistortionCoefficients' and the number '2' or '3'.

'EstimateTangentialDistortion' — Estimate tangential distortion flagfalse (default) | logical scalar

Estimate tangential distortion flag, specified as the comma-separated pair of consisting of 'EstimateTangentialDistortion' and the logical scalar true or false. When you set the logical to true, the object estimates the tangential distortion. When you set the logical to false, the tangential distortion is negligible.

Properties

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Intrinsic camera parameters:

IntrinsicMatrix — Projection matrix3-by-3 identity matrix

Projection matrix, specified as a 3-by-3 identity matrix. The object uses the following format for the matrix format:

The coordinates [cx cy] represent the optical center (the principal point), in pixels. When the x and y axis are exactly perpendicular, the skew parameter, s, equals 0.

fx = F*sx
fy = F*sy
F, is the focal length in world units, typically expressed in millimeters.
[sx, sy] are the number of pixels per world unit in the x and y direction respectively.
fx and fy are expressed in pixels.


Camera lens distortion:

RadialDistortion — Radial distortion coefficients[0 0 0] (default) | 2-element vector | 3-element vector

Radial distortion coefficients, specified as either a 2- or 3-element vector. When you specify a 2-element vector, the object sets the third element to 0. Radial distortion occurs when light rays bend more near the edges of a lens than they do at its optical center. The smaller the lens, the greater the distortion. The camera parameters object calculates the radial distorted location of a point. You can denote the distorted points as (xdistorted, ydistorted), as follows:

xdistorted = x(1 + k1*r2 + k2*r4 + k3*r6)

ydistorted= y(1 + k1*r2 + k2*r4 + k3*r6)

x, y = undistorted pixel locations
k1, k2, and k3 = radial distortion coefficients of the lens
r2 = x2 + y2

Typically, two coefficients are sufficient. For severe distortion, you can include k3. The undistorted pixel locations appear in normalized image coordinates, with the origin at the optical center. The coordinates are expressed in world units.

TangentialDistortion — Tangential distortion coefficients[0 0]' (default) | 2-element vector

Tangential distortion coefficients, specified as a 2-element vector. Tangential distortion occurs when the lens and the image plane are not parallel. The camera parameters object calculates the tangential distorted location of a point. You can denote the distorted points as (xdistorted, ydistorted), as follows:

xdistorted = x + [2 * p1 * y + p2 * (r2 + 2 * x2)]

ydistorted = y + [p1 * (r2 + 2*y2) + 2 * p2 * x]

x, y = undistorted pixel locations
p1 and p2 = tangential distortion coefficients of the lens
r2 = x2 + y2

The undistorted pixel locations appear in normalized image coordinates, with the origin at the optical center. The coordinates are expressed in world units.


Extrinsic camera parameters:

RotationMatrices — 3-D rotation matrix3-by-3-by-P matrix (read-only)

3-D rotation matrix, specified as a 3-by-3-by-P, with P number of pattern images. Each 3-by-3 matrix represents the same 3-D rotation as the corresponding vector.

The following equation provides the transformation that relates a world coordinate [X Y Z] and the corresponding image point [x y]:

R is the 3-D rotation matrix.
t is the translation vector.
K is the IntrinsicMatrix.
s is a scalar.

This equation does not take distortion into consideration. Distortion is removed by the undistortImage function.

TranslationVectors — Camera translationsM-by-3 matrix | []

Camera translations, specified as an M-by-3 matrix. This matrix contains translation vectors for M images. The vectors contain the calibration pattern that estimates the calibration parameters. Each row of the matrix contains a vector that describes the translation of the camera relative to the corresponding pattern, expressed in world units.

The following equation provides the transformation that relates a world coordinate [X Y Z] and the corresponding image point [x y]:

R is the 3-D rotation matrix.
t is the translation vector.
K is the IntrinsicMatrix.
s is a scalar.

This equation does not take distortion into consideration. Distortion is removed by the undistortImage function.

You must set the RotationVectors and TranslationVectors properties in the constructor to ensure that the number of rotation vectors equals the number of translation vectors. Setting only one property but not the other results in an error.


Estimated camera parameter accuracy:

MeanReprojectionError — Average Euclidean distancenumeric value (read-only)

Average Euclidean distance between reprojected and detected points, specified as a numeric value in pixels.

ReprojectionErrors — Estimated camera parameters accuracyM-by-2-by-P array

Estimated camera parameters accuracy, specified as an M-by-2-by-P array of [x y] coordinates. The [x y] coordinates represent the translation in x and y between the reprojected pattern key points and the detected pattern key points. The values of this property represent the accuracy of the estimated camera parameters. P is the number of pattern images that estimates camera parameters. M is the number of keypoints in each image.


Estimate camera parameters settings:

NumPatterns — Number of calibrated patternsinteger

Number of calibration patterns that estimates camera extrinsics, specified as an integer. The number of calibration patterns equals the number of translation and rotation vectors.

WorldPoints — World coordinatesM-by-2 array | []

World coordinates of key points on calibration pattern, specified as an M-by-2 array. M represents the number of key points in the pattern.

WorldUnits — World points units'mm' (default) | string

World points units, specified as a string. The string describes the units of measure.

EstimateSkew — Estimate skew flagfalse (default) | logical scalar

Estimate skew flag, specified as a logical scalar. When you set the logical to true, the object estimates the image axes skew. When you set the logical to false, the image axes are exactly perpendicular.

NumRadialDistortionCoefficients — Number of radial distortion coefficients2 (default) | 3

Number of radial distortion coefficients, specified as the number '2' or '3'.

EstimateTangentialDistortion — Estimate tangential distortion flagfalse (default) | logical scalar

Estimate tangential distortion flag, specified as the logical scalar true or false. When you set the logical to true, the object estimates the tangential distortion. When you set the logical to false, the tangential distortion is negligible.

Output Arguments

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cameraParams — Camera parameterscameraParameters object

Camera parameters, returned as a cameraParameters object. The object contains the intrinsic, extrinsic, and lens distortion parameters of a camera.

Examples

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Remove Distortion from an Image Using the cameraParameters Object

This example shows you how to use the cameraParameters object in a workflow to remove distortion from an image. The example creates a cameraParameters object manually. In practice, use the estimateCameraParameters or the cameraCalibrator app to derive the object.

% Create a cameraParameters object manually.
    IntrinsicMatrix = [715.2699   0       0;
                          0     711.5281  0;
                     565.6995  355.3466  1];
    radialDistortion = [-0.3361 0.0921];
    cameraParams = cameraParameters('IntrinsicMatrix', IntrinsicMatrix, 'RadialDistortion', radialDistortion);

% Remove distortion from the image.
    I = imread(fullfile(matlabroot, 'toolbox', 'vision', 'visiondemos', 'calibration', 'fishEye', 'image01.jpg'));
    J = undistortImage(I, cameraParameters);

% Display the original and undistorted images.
    figure; imshowpair(imresize(I, 0.5), imresize(J, 0.5), 'montage');
    title('Original Image (left) vs. Corrected Image (right)');

References

[1] Zhang, Z. "A flexible new technique for camera calibration". IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 22, No. 11, pp. 1330–1334, 2000.

[2] Heikkila, J, and O. Silven. "A Four-step Camera Calibration Procedure with Implicit Image Correction", IEEE International Conference on Computer Vision and Pattern Recognition, 1997.

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