How to remove few part of a circle?

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.

Answer 1

[Image Analyst]

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 :

1. the circle perimeter alone,
2. the part inside the circle, or
3. the part outside the circle.

Please explain better or attach a desired output image.

[Zara Khan]

Image Analyst: Circle perimeter will be visible when it will get image object only. It will not visible when going through background . I have attached a picture to explain how the ouput will be.

[Image Analyst]

Assuming when you generate each circle, you have the (x,y) coordinates of it, simply erase them:

for k = 1 : length(x)
    col = round(x);
    row = round(y);
    binaryImage(row, col) = false;
end

[Zara Khan]

clc;
close all;
clear;
workspace;
a = imread('img.png');
    bwimg =bwareafilt(~a, 1); 
s=regionprops(bwimg,'Orientation','Centroid','MajorAxisLength','MinorAxisLength');
circleCenterX =s.Centroid(1);
circleCenterY =s.Centroid(2);
diameter = mean([s.MajorAxisLength s.MinorAxisLength],2);
figure;
imshow(bwimg);
set (gca,'TickLabelInterpreter','none');
set(gca,'fontweight','bold','fontsize',12);
set(gca,'color','black');
get(0,'Factory');
hold on
for n=1:8
    r=n*diameter/16;    
t=0:0.001:2*pi;
x = circleCenterX + r* sin(t);
y = circleCenterY + r * cos(t);
plot(x,y, 'LineWidth', 2);
 
 for k=1:length(x);
    col=round(x);
    row=round(y);
   bwimg(row,col)=false;
 end
 
end

This is not working .

[Image Analyst]

Attach 'img.png'

[Zara Khan]

Image Analyst: I have attached the 'img.png'

[Zara Khan]

can you helo me in doing this please

[Image Analyst]

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');

[madhan ravi]

+1, really admirable ?

[Zara Khan]

Image Analyst:

Thank you for your effort sir. But I have tried to show how will be my desired output by adding the "i.png" where all circle permiters are in black colors. But actually it will be in colors.Only the portion where its getting background will be ommited just like your final image. But here all are perimeters are in black. Is this possible to make them colors?

[Image Analyst]

Sure, just change it to an RGB image.

	rgbImage(row,col, 1)  = redColor;
	rgbImage(row,col, 2)  = greenColor;
	rgbImage(row,col, 3)  = blueColor;

Of course you will need to change those values every circle if you want different colors. They should be in the range 0-255.

[Zara Khan]

How to change this for colour one ? please help

[Image Analyst]

Not sure what you mean. The code above will work for any color, just put in the right values.

[Zara Khan]

% 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
 
 
 

I want to change this portion .

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

I want to make the binary image to any colour where it is at the circle. I am using colour code but its not working .

After making this I want to chane the image black background to white keeping the image circle portion intact .

[Image Analyst]

Binary images are only black or white. You can use an RGB image though:

rgbImage(row,col, 1) = redValue;
rgbImage(row,col, 2) = greenValue;
rgbImage(row,col, 3) = blueValue;

[Zara Khan]

for k=1:length(x)

col=round(x(k));

row=round(y(k));

binaryImage(row,col) = false;

How to change the false to any other colour?

[Image Analyst]

Again, you'd have to use an RGB image.

[Zara Khan]

How can make the black background to white ,keeping circle portion instead ? Changing the black background to white making full image white.