imregcorr

Estimate geometric transformation that aligns two 2-D images using phase correlation

Syntax

tform = imregcorr(moving,fixed)

tform = imregcorr(moving,Rmoving,fixed,Rfixed)

tform = imregcorr(___,tformType)

tform = imregcorr(___,"Window",window)

[tform,peakcorr] = imregcorr(___)

Description

tform = imregcorr(moving,fixed) estimates the geometric transformation that aligns an image, moving, with a reference image, fixed. The function returns a geometric transformation object, tform, that maps pixels in moving to pixels in fixed.

tform = imregcorr(moving,Rmoving,fixed,Rfixed) estimates the geometric transformation that aligns an image, moving, with a reference image, fixed. Rmoving and Rfixed are spatial referencing objects that contain spatial information about the moving and fixed images, respectively. The transformation object returned, tform, defines the point mapping in the world coordinate system.

tform = imregcorr(___,tformType) also specifies the type of transformation, tformType.

tform = imregcorr(___,"Window",window) also specifies whether to perform windowing in the frequency domain. To increase the stability of registration results, specify window as true. However, if the common features in your images are oriented along the edges, then setting window to false can sometimes provide superior registration results.

[tform,peakcorr] = imregcorr(___) also returns the peak correlation, peakcorr, of the phase difference between the two images.

Examples

Register Images Using Phase Correlation

Read a reference image into the workspace.

fixed  = imread("cameraman.tif");

Create a synthetic moving image by scaling and rotating the fixed image.

scaleFactor = 2.3;
theta = 20;
translation = [0 0];
tform = simtform2d(scaleFactor,theta,translation);
moving = imwarp(fixed,tform);

Add synthetic noise to the moving image.

moving = moving + uint8(10*rand(size(moving)));

Display the fixed and the moving image alongside each other.

imshowpair(fixed,moving,"montage")

Estimate the transformation needed to align the images using imregcorr.

tformEstimate = imregcorr(moving,fixed);

Apply the estimated geometric transform to the moving image. Specify the "OutputView" name-value argument to obtain a registered image the same size and with the same world limits as the reference image.

Rfixed = imref2d(size(fixed));
movingReg = imwarp(moving,tformEstimate,"OutputView",Rfixed);

View the original image and the registered image side-by-side to check the registration. Then view the registered image overlaid on the original using the "falsecolor" option to highlight any areas where the images differ.

imshowpair(fixed,movingReg,"montage")

imshowpair(fixed,movingReg,"falsecolor");

Input Arguments

moving — Image to be registered

grayscale image | binary image | RGB image

Image to be registered, specified as a grayscale, binary, or RGB image. If you specify an RGB image, imregcorr converts it to a grayscale image using rgb2gray before processing.

Note

The aspect ratio of moving affects the output transform tform. For best results, use a square image.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | logical

fixed — Reference image

grayscale image | binary image | RGB image

Reference image in the target orientation, specified as a grayscale, binary, or RGB image. imregcorr converts RGB images to grayscale using rgb2gray before processing.

Note

The aspect ratio of fixed affects the output transform tform. For best results, use a square image.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | logical

tformType — Type of transformation to estimate

"similarity" (default) | "rigid" | "translation"

Type of transformation to estimate, specified as one of these values.

Value	Description
"translation"	Translation transformation
"rigid"	Rigid transformation: translation and rotation
"similarity"	Similarity transformation: translation, rotation, and isotropic scaling When using the "similarity" option, the phase correlation algorithm is only scale invariant within some range of scale difference between the fixed and moving images. imregcorr limits the search space to scale differences within the range [1/4, 4]. imregcorr does not detect scale differences less than 1/4 or greater than 4.

Data Types: char | string

Rmoving — Spatial referencing information associated moving image

imref2d object

Spatial referencing information associated with the image to be registered, specified as an imref2d object.

Rfixed — Spatial referencing information associated with fixed image

imref2d object

Spatial referencing information associated with the fixed image, specified as an imref2d object.

window — Use windowing to suppress spectral leakage effects

true or 1 (default) | false or 0

Use windowing to suppress spectral leakage effects in the frequency domain, specified as a numeric or logical 1 (true) or 0 (false). When true, the imregcorr function performs windowing using a Blackman filter.

Output Arguments

tform — Geometric transformation

transltform2d object | rigidtform2d object | simtform2d object

Geometric transformation, returned as a geometric transformation object according to the type of transformation, tformType.

tformType	Geometric Transformation Object
"translation"	transltform2d
"rigid"	rigidtform2d
"similarity"	simtform2d

peakcorr — Peak correlation of phase difference

numeric scalar

Peak correlation value of the phase difference between the two images, returned as a numeric scalar.

Tips

• If your image is of type double, you can achieve performance improvements by casting the image to single with im2single before registration. Input images of type double cause the algorithm to compute FFTs in double.

References

[1] Reddy, B. S. and Chatterji, B. N., An FFT-Based Technique for Translation, Rotation, and Scale-Invariant Image Registration, IEEE Transactions on Image Processing, Vol. 5, No. 8, August 1996

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

imregcorr supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced in R2014a

R2022b: Returns new geometric transformation objects

Starting in R2022b, most Image Processing Toolbox™ functions create and perform geometric transformations using the premultiply convention. Accordingly, the imregcorr function now returns the output argument tform as an transltform2d, rigidtform2d, or simtform2d object, which support the premultiply convention. Before, the function returned tform as an affine2d object, which supports the postmultiply convention. For more information, see Migrate Geometric Transformations to Premultiply Convention.

R2021b: Support for thread-based environments

imregcorr now supports thread-based environments.