How to obtain an angular segment with its vertex on the center from a circular image?
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Jyothis Jose
on 1 May 2014
Commented: Image Analyst
on 2 Feb 2017
I have a circular image. I need to extract eight equal angular segment from it. Can anyone help me with the matlab code for this?
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Accepted Answer
Image Analyst
on 1 May 2014
xCenter = 12;
yCenter = 10;
theta = 0 : 0.01 : 2*pi;
radius = 5;
x = radius * cos(theta) + xCenter;
y = radius * sin(theta) + yCenter;
plot(x, y);
axis square;
xlim([0 20]);
ylim([0 20]);
grid on;
Adjust the starting and ending theta to be what you need them to be, then pass x and y into poly2mask() to get a binary image which can then multiply by your image.
mask = poly2mask(x,y,size(rgbImage, 1), size(rgbImage, 2));
% Mask the image using bsxfun() function
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, class(rgbImage)));
7 Comments
Image Analyst
on 2 Feb 2017
It's the same code, using bsxfun. Change the ending angle if you don't want a full circle.
xCenter = 128;
yCenter = 128;
theta = 0 : 0.01 : 2*pi/3;
radius = 100;
x = radius * cos(theta) + xCenter;
y = radius * sin(theta) + yCenter;
plot(x, y);
axis square;
xlim([0 20]);
ylim([0 20]);
grid on;
% Tack on the center
x = [xCenter, x, xCenter];
y = [yCenter, y, yCenter];
% Read in gray scale image. Actually can be anything - RGB or gray scale.
grayImage = imread('cameraman.tif');
subplot(2,2,1);
imshow(grayImage, []);
axis on;
% Create mask
mask = poly2mask(x,y,size(grayImage, 1), size(grayImage, 2));
subplot(2,2,2);
imshow(mask, []);
axis on;
% Mask the image using bsxfun() function
maskedGrayImage = bsxfun(@times, grayImage, cast(mask, class(grayImage)));
subplot(2,2,3:4);
imshow(maskedGrayImage, []);
axis on;
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/185788/image.png)
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