Asked by Zara Khan
on 14 Mar 2019 at 15:46

I have drawn few circles using plot function. How can remove few parts of circle perimeter? The concept is that circle perimter will be OFF when gets background and ON when gets image object.

Answer by Image Analyst
on 14 Mar 2019 at 18:50

Try this:

clc; % Clear the command window.

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;

rgbImage = imread('img.png');

% Get the dimensions of the image.

% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.

[rows, columns, numberOfColorChannels] = size(rgbImage)

if numberOfColorChannels > 1

% It's not really gray scale like we expected - it's color.

% Use weighted sum of ALL channels to create a gray scale image.

% grayImage = rgb2gray(rgbImage);

% ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,

% which in a typical snapshot will be the least noisy channel.

grayImage = rgbImage(:, :, 2); % Take green channel.

else

grayImage = rgbImage; % It's already gray scale.

end

% Now it's definitely gray scale with range of 0 to 255.

% Display the image.

subplot(2, 2, 1);

imshow(grayImage, []);

title('Original Image', 'FontSize', fontSize, 'Interpreter', 'None');

axis('on', 'image');

hp = impixelinfo();

%------------------------------------------------------------------------------

% Set up figure properties:

% Enlarge figure to full screen.

set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);

% 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 ImageAnalyst', 'NumberTitle', 'Off')

drawnow;

binaryImage = bwareafilt(~grayImage, 1);

props = regionprops(binaryImage,'Orientation','Centroid','MajorAxisLength','MinorAxisLength');

circleCenterX = props.Centroid(1);

circleCenterY = props.Centroid(2);

% Get the average of the min and max diameter.

diameter = mean([props.MajorAxisLength, props.MinorAxisLength], 2)

% Display the image.

subplot(2, 2, 2);

imshow(binaryImage);

title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');

axis('on', 'image');

hp = impixelinfo();

hold on

drawnow;

circumference = 2 * pi * props.MajorAxisLength;

t = linspace(0, 2*pi, 1.5 * circumference);

fprintf('Writing black to the %d points along the circles.', length(t));

for n = 1 : 8

fprintf('Processing circle #%d.\n', n);

r = n * diameter / 16;

x = circleCenterX + r * sin(t);

y = circleCenterY + r * cos(t);

plot(x,y, 'LineWidth', 2);

% Make the binary image black where it is at the circle.

for k=1:length(x)

col=round(x(k));

row=round(y(k));

binaryImage(row,col) = false;

end

end

% Display the final image.

subplot(2, 2, 3);

imshow(binaryImage);

title('Final Image', 'FontSize', fontSize, 'Interpreter', 'None');

axis('on', 'image');

Note: same code is also in your other question : Click for older question

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## 9 Comments

## Adam (view profile)

Direct link to this comment:https://www.mathworks.com/matlabcentral/answers/450112-how-can-i-remove-few-parts-of-circle-perimeter#comment_681156

## Zara Khan (view profile)

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## Adam Danz (view profile)

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## Image Analyst (view profile)

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