How to divide a rectangle into 4 regions?

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joynob ahmed 2020-4-5

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https://ww2.mathworks.cn/matlabcentral/answers/515513-how-to-divide-a-rectangle-into-4-regions

评论： joynob ahmed 2020-4-25

I want to find the boundary pixels lying on the lines connecting the center of the mass with the vertices. These four points make it possible to divide the boundary rectangle into four parts which are not the same length. In the next step i want to calculate the distance between the border rectangle and the image edge for each part of the borderline. I have attached the images on which I am working and what I want to do.

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Image Analyst 2020-4-5

编辑：Image Analyst 2020-4-5

在 MATLAB Online 中打开

But what about the fact that the centroid of the binary blob does not lie where the bounding box diagonals cross? Which of those two locations do you want to take as the center?

% Initialization steps.
clc;    % Clear the command window.
fprintf('Beginning to run %s.m ...\n', mfilename);
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
mask = imread('image.bmp');
imshow(mask);
[rows, columns, numberOfColorChannels] = size(mask)
% Binarize the RGB image
if numberOfColorChannels > 1
	mask = mask(:,:,1) > 128;
	numberOfColorChannels = 1;
end
% Get rid of white rectangular frame surrounding the blob.
mask = imclearborder(mask);
% Fill holes and take the largest blob.
mask = bwareafilt(imfill(mask, 'holes'), 1);
% Fill holes and take the largest blob.
mask = bwareafilt(imfill(mask, 'holes'), 1);
% Show updated mask.
imshow(mask);
props = regionprops(mask, 'BoundingBox', 'Centroid');
% Now get the boundary
boundaries = bwboundaries(mask);
boundaries = boundaries{1};
xBoundary = boundaries(:, 2);
yBoundary = boundaries(:, 1);
hold on;
% Plot red x at the centroid.
plot(props.Centroid(1), props.Centroid(2), 'rx', 'MarkerSize', 400, 'LineWidth', 2);
% Plot bounding box as a yellow rectangle.
rectangle('Position', props.BoundingBox, 'EdgeColor', 'y');
% Plot boundary in red.
plot(xBoundary, yBoundary, 'r-', 'LineWidth', 2);
% Draw lines across diagonals of bounding box.
x1 = props.BoundingBox(1)
y1 = props.BoundingBox(2)
x2 = props.BoundingBox(1) + props.BoundingBox(3)
y2 = props.BoundingBox(2) + props.BoundingBox(4)
line([x1, x2], [y1, y2], 'Color', 'y', 'LineWidth', 2);
line([x2, x1], [y1, y2], 'Color', 'y', 'LineWidth', 2);
% Find midpoints of the box.
xMid = mean([x1, x2])
yMid = mean([y1, y2])
% Get line from upper left to lower right.
coefficients1 = polyfit([x1, x2], [y1, y2], 1)
xLine = 1 : columns;
yLine1 = polyval(coefficients1, xLine);
% Get line from upper right to lower left.
coefficients2 = polyfit([x2, x1], [y1, y2], 1)
yLine2 = polyval(coefficients2, xLine);
% % Get distance of the top line of the bounding box to all points in the upper triangle
% validIndexes = x < xMid & yBoundary < yLine1 & yBoundary < yLine2;
% x = xBoundary(validIndexes);
% y = yBoundary(validIndexes);
% distancesTop = y1 - y;