How to remove few part of a circle?

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Zara Khan 2019-3-2

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评论： Zara Khan 2019-11-4

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I am drawing different radius circles over an image object using simple plot function. How can remove circle portion from background and will only left the portion that is going through image object.

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回答（1 个）

Image Analyst 2019-3-2

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在 MATLAB Online 中打开

You can make a mask and then use it to erase the part of the image you don't want

binaryImage(mask) = false; % Erase in mask

However your wording is so ambiguous, I don't know what the mask should be :

the circle perimeter alone,
the part inside the circle, or
the part outside the circle.

Please explain better or attach a desired output image.

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Image Analyst 2019-3-14

在 MATLAB Online 中打开

Yes, 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');