rectifyStereoImages Rotation Matrix output is coming out 3 x 4 instead of 3 x 3

Hi, i am using the Matlab function rectifyStereoImages to calculate the camera1 rotation matrix and camera 2 rotation matrix (R1 and R2) as suggested in the documentation.

Documentation Example :-

[___,camMatrix1,camMatrix2,R1,R2] = rectifyStereoImages(I1,I2,stereoParams) returns the 3-by-4 camera projection matrices camMatrix1 and camMatrix2 for the rectified cameras, and the corresponding rectification rotation matrices, R1 and R2.

R1 and R2 should be 3 x 3 as said in the documentation.

Here is what i am doing :-

load("CameraCalib.mat")
LeftImage = imread("Left.png");
RightImage = imread("Right.png");
[~, CamMatLeft, CamMatRight, R1, R2] = rectifyStereoImages(LeftImage, RightImage, CameraCalib);

according to the documentation R1 and R2 should be 3 x 3 but in my workspace i am getting R1 and R2 to be 3 x 4 projection matrices.

Any idea what am i doing wrong here ? If so how should i fix this to get the desired matrices ?

Answer 1

[chicken vector]

It looks like you are missing two output arguments, so what you call R1 is actually camMatrix1.

The default syntax of the function is:

[J1,J2,reprojectionMatrix] = rectifyStereoImages(I1,I2,stereoParams)

It means that when you use this:

[___,camMatrix1,camMatrix2,R1,R2] = rectifyStereoImages(I1,I2,stereoParams)

^This line takes into account the three output J1, J2 and reprojectionMatrix.

You need to do:

load("CameraCalib.mat")
LeftImage = imread("Left.png");
RightImage = imread("Right.png");
[~, ~, ~, CamMatLeft, CamMatRight, R1, R2] = rectifyStereoImages(LeftImage, RightImage, CameraCalib);

[Soumya Dubey]

Thanks a lot. Just a quick question.

Can i use these Matrices R1 (3 x 3) and R2 (3 x 3) along with the projection matrcies P1 (3 x 4) and P2 (3 x 4) to rectify any pair of images i get from the camera that i calibrated ?

Thanks.

[chicken vector]

I am not sure. If the stereo parameters remain the same, probably yes, but I don't know how much time you can save by doing that.

Anyway, you can try to use the function on different frames and see if the rotation matricees are the same.

[Soumya Dubey]

Yeah it worked. Thanks.