I want to calculate the affine transformation matrix (rotation, translation and scaling) for the binary image

I want to calculate this matrix consisting of rotation, translation and scaling of binary image, how can I calculate this matrix using Matlab in one loop

Thanks in advance

Answer 1

[Umeshraja]

Hi @Haytham Ali,

I understand that you wanted to perform an affine transformation on a binary image. You can achieve this using the 'affinetform2d' and 'imwarp' functions of MATLAB's Image Processing Toolbox..

Below is a demonstration of how you can calculate the transformation matrix that includes rotation, scaling, and translation, and then apply it to your binary image.

close all;

% Load a grayscale image
img = imread('cameraman.tif');

% Convert the image to binary using a threshold
% Here, we use a threshold of 128 for demonstration
I = img > 128;

% Define transformation parameters
Theta = 90; % angle of rotation
Scale = 1.5;
a = 2; % translation along x-axis
b = 4; % translation along y-axis

% Calculate the transformation matrix
%Rotation
Thrad = Theta * pi / 180;
R = [ cos(Thrad) -sin(Thrad)  0;
      sin(Thrad)  cos(Thrad)  0;
            0          0      1   ];

%Scaling
S = [Scale 0    0;
       0  Scale 0;
       0   0    1  ];

%Transform
T = [ 1  0 a;
      0  1 b;
      0  0  1   ];

% Combine the transformations
RST = R * S * T;

% Create affine transformation object
t_aff = affinetform2d(RST);

% Apply transformation to the binary image
binaryImage_affine = imwarp(I, t_aff);

figure;
imshow(I)
title("Original")

% Display the transformed binary image
figure;
imshow(binaryImage_affine);
title("Transformed Binary Image");

For more information, refer to the following documentation:

• affinetform2d : https://www.mathworks.com/help/images/ref/affinetform2d.html
• imwrap: https://www.mathworks.com/help/images/ref/imwarp.html

I hope it helps!