calculate the width and height of the rectangle in this image automatically?

How can I calculate the width and height of the rectangle in this image automatically? to use them in the next step

[Dina Abd El-twab]

Answer 1

[Image Analyst]

Seems to work for me:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;

folder = pwd;
baseFileName = 'image.png';
fullFileName = fullfile(folder, baseFileName);
rgbImage = imread(fullFileName);
% Display the original image.
subplot(2, 2, 1);
imshow(rgbImage, []);
axis('on', 'image');
caption = sprintf('Original Color Image\n"%s"', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by Image Analyst', 'NumberTitle', 'Off')

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);

% Get the yellow mask.
yellowMask = redChannel == 255 & greenChannel == 255 & blueChannel == 0;
subplot(2, 2, 2);
imshow(yellowMask);
grid on;
title('Yellow Mask', 'FontSize', fontSize, 'Interpreter', 'None');
yellowMask = imfill(yellowMask, 'holes');
yellowMask = bwareafilt(yellowMask, 1);
subplot(2, 2, 3);
imshow(yellowMask);
grid on;
title('Yellow Mask, Filled', 'FontSize', fontSize, 'Interpreter', 'None');

% Find the Centroid, Equivalent Circular Diameter, and Bounding Box.
props = regionprops(yellowMask, 'Centroid', 'EquivDiameter', 'BoundingBox');
fprintf('Yellow Box Width = %d.\nYellow Box Height = %d.\n', props.BoundingBox(3), props.BoundingBox(4));
viscircles(props.Centroid, props.EquivDiameter/2);

% Display the original image.
subplot(2, 2, 4);
imshow(rgbImage, []);
axis('on', 'image');
caption = sprintf('With red circle centered over yellow square');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
viscircles(props.Centroid, props.EquivDiameter/2);

[Dina Abd El-twab]

Thank you very much Image Analyst for your great help, but I have another question, why every time I execute the program, the sides of the rectangle disappear in the original color image and yellow mask image as the image i attach .So ,I want to save the 4 plots to be 4 seperate images in my current folder,could yo help me to make them saved images not plots because i want to use them in another steps?

[Dina Abd El-twab]

Image Analyst

[Image Analyst]

Dina:

I think you were just unlucky when it decided to shrink your image for display. The one edge was a row it decided to eliminate when it subsampled your image for display. Don't worry though, because the original image still has that edge in there. You can save it with imwrite():

uint8Image = uint8(255 * yellowMask);
imwrite(uint8Image, 'Yellow Mask.png');

If you want the circle in the saved image, you'll have to burn it into the image. First get a circle mask using the FAQ: https://matlab.fandom.com/wiki/FAQ#How_do_I_create_a_circle.3F

Then with the (x,y) you got from the FAQ code, burn it into the image and then call imwrite:

circleColor = [255, 0, 0]; % Red or whatever color you want to use.  Format is [R, G, B].
for k = 1 : length(x)
    row = y(k);
    col = x(k);
    redChannel(row, col) = circleColor(1);
    greenChannel(row, col) = circleColor(2);
    blueChannel(row, col) = circleColor(3);
end
rgbImage = cat(3, redChannel, greenChannel, blueChannel);
imwrite(rgbImage, 'Red Circle.png');

[Dina Abd El-twab]

imageSizeX = 286;
imageSizeY = 322;
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX =    ;
centerY =    ;
radius = 36.4050;
BW1 = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.

imwrite(BW1,'BW1.png');

[Dina Abd El-twab]

It is ok for the yellow mask image , but for the image of the circle , how can i extract ( centerX & centerY) from the "centroid "that you obtainned by regionprop command?

Image Analyst

[Image Analyst]

You have to segment out the circle first. For example maybe you can threshold it and get rid of blobs touching the border then take the largest blob. Something like

mask = grayImage < someValue;
mask = imclearborder(mask);
mask = bwareafilt(mask, 1);
props = regionprops(mask, 'Centroid')
xCenter = props.Centroid(1);
yCenter = props.Centroid(2);
hold on;
plot(xCenter, yCenter, 'r+', 'MarkerSize', 30);

See my visually interactive thresholding app: in my File Exchange