Extract pixels inside the area between 2 edge lines

Hello,

I would like to detect all the pixels of an BW image which are enclosed into the area of a polybuffer. About the polybuffer, I have got the x and y coordinates of the 2 edge lines whcih constitute the polybuffer itself. How can I do it?

Thank you so much for your help!

[Matt J]

What is a polybuffer? Please show us the image and the input variables that you have, so we can better demonstrate solutions..

[Riccardo Rossi]

Hi Matt,

I have uploaded the image I and the POLYOUT (with x and y coordinates). Basically I would like to select all the pixels of I which are enclosed inside the area of polyout., as you can easily see by running the following code:

imshow(I)
hold on;
plot(POLYOUT.Vertices(:,2),POLYOUT.Vertices(:,1),'g','LineWidth',3);

Answer 1

[Matt J]

[m,n]=size(I);
 
 mask=poly2mask(POLYOUT.Vertices(:,2),POLYOUT.Vertices(:,1), m,n); 

pixels=I(mask)

[Riccardo Rossi]

It is run, and how can i get the x y coordinates of "pixels" variable? Thank you so much again

[Matt J]

[y,x]=find(mask);

Once you have the mask, you can also get both together with,

stats = regionprops(mask,I, 'PixelList','PixelValues')

Answer 2

[Diwakar Diwakar]

% Create a black and white image
image = zeros(500, 500);
image(200:300, 200:300) = 1;  % Add a square shape

% Display the original image
subplot(1, 2, 1);
imshow(image);
title('Original Image');

% Coordinates of the edge lines
edge_line1 = [100, 100; 200, 100; 200, 200; 100, 200];
edge_line2 = [150, 150; 250, 150; 250, 250; 150, 250];

% Detect enclosed pixels
enclosed_pixels = detect_enclosed_pixels(image, edge_line1, edge_line2);

% Display the enclosed pixels
subplot(1, 2, 2);
imshow(enclosed_pixels);
title('Enclosed Pixels');

function enclosed_pixels = detect_enclosed_pixels(image, edge_line1, edge_line2)
    % Create binary mask
    mask = false(size(image));

    % Define the polygon points using edge lines
    polygon_points = [edge_line1; flip(edge_line2, 1)];

    % Get the minimum and maximum coordinates for the polygon
    min_x = min(polygon_points(:, 1));
    max_x = max(polygon_points(:, 1));
    min_y = min(polygon_points(:, 2));
    max_y = max(polygon_points(:, 2));

    % Create a binary mask for the polygon region
    polygon_mask = poly2mask(polygon_points(:, 1), polygon_points(:, 2), size(image, 1), size(image, 2));

    % Extract the region of interest using the polygon mask
    roi = image(min_y:max_y, min_x:max_x);

    % Apply the polygon mask to the region of interest
    roi_masked = roi & polygon_mask(min_y:max_y, min_x:max_x);

    % Create a new binary mask with the enclosed region
    enclosed_pixels = false(size(image));
    enclosed_pixels(min_y:max_y, min_x:max_x) = roi_masked;
end