Reading and saving values of a matrix by circular shapes

Given a matrix of a greyscale image, I am trying to read this matrix using circular shapes (known centroid and radii). Then, is it possible to store those values of the greyscale matrix in a vertical matrix?

Thank you in advance for your help!

Answer 1

[Zinea]

Hi Juan Carlos Alvarez Fernandez,

It is possible to sample values from a greyscale image matrix using circular shapes with known centroids and radii, and then store those sampled values in a vertical matrix (i.e. a column vector).

You can follow the following steps:

1. Sample the greyscale image: Iterate over the pixels of the greyscale image and determine which pixels fall within the defined circular region. This involves checking if the distance between the pixel and the centroid of the circle is less than or equal to the radius of the circle.
2. Create a vertical matrix: As you find pixels that fall within the circular region, you an append their greyscale values to a vertical matrix.

Here is an example MATLAB script that uses a dummy greyscale image matrix, a predefined centroid and radius that create a vertical matrix with sampled greyscale values:

% Dummy greyscale image matrix (10x10) with values from 0 to 255 
image_matrix = uint8([ 
    255, 200, 200, 200, 200, 200, 200, 200, 200, 255; 
    200, 100, 100, 100, 100, 100, 100, 100, 100, 200; 
    200, 100, 50,  50,  50,  50,  50,  50,  100, 200; 
    200, 100, 50,  25,  25,  25,  25,  50,  100, 200; 
    200, 100, 50,  25,  0,   0,   25,  50,  100, 200; 
    200, 100, 50,  25,  0,   0,   25,  50,  100, 200; 
    200, 100, 50,  25,  25,  25,  25,  50,  100, 200; 
    200, 100, 50,  50,  50,  50,  50,  50,  100, 200; 
    200, 100, 100, 100, 100, 100, 100, 100, 100, 200; 
    255, 200, 200, 200, 200, 200, 200, 200, 200, 255; 
    ]); 

centroid = [5, 5];  
radius = 3;  
vertical_matrix = sample_circle(image_matrix, centroid, radius); 
disp(vertical_matrix); 

   100
    50
    50
    50
    50
    50
    50
    25
    25
    25
    25
   100
    50
    25
     0
     0
    25
    50
    50
    25
     0
     0
    25
    50
    25
    25
    25
    25
    50

function vertical_matrix = sample_circle(image_matrix, centroid, radius) 
% Initialize an empty array to store the pixel values 
vertical_matrix = []; 

% Calculate the size of the image 
[height, width] = size(image_matrix); 

% Loop over every pixel in the image 
for x = 1:width 
    for y = 1:height 
        % Check if the current pixel is within the circle 
        if is_within_circle(x, y, centroid, radius) 
            % If it is, add the pixel value to the vertical matrix 
            pixel_value = image_matrix(y, x); 
            vertical_matrix(end+1, 1) = pixel_value;  
        end 
    end 
end 
end 

function result = is_within_circle(x, y, centroid, radius) 
% Calculate the distance from the pixel to the centroid 
distance = sqrt((x - centroid(1))^2 + (y - centroid(2))^2); 
% Check if the distance is less than or equal to the radius 
result = distance <= radius; 
end