Create an image (pixels) circle with slices (not from the center) and paint each slice a different color

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Moshe Peleg 2021-8-13

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评论： Moshe Peleg 2021-9-24

I am trying to create an image of a circle and divide the circle into known parts (start from the shell of the circle) and give each part (slice) a different color (or gray level).

I am having difficulty how to restrict each slice between two lines and the relevant arc of the circle that completes the slice.

please see the attached picture to understand what i mean.(sorry that the painting wasnot complete - just to help understand the question)

please refer only to the slices in red (ignore the blue one)

thank you very much for your time and help!.

here is the code i found to create the circle:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = 640;
imageSizeY = 480;
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = 320;
centerY = 240;
radius = 200;
circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
%subplot(2, 1, 1);
imshow(circlePixels) ;
colormap([0 0 0; 1 1 1]);
title('Binary image of a circle', 'FontSize', fontSize);
new_im = im2double(circlePixels);
imshow(new_im);

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Answer 1

Bjorn Gustavsson 2021-8-13

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(The background image looked rather nice if you ask me...) If you want to find those wedge-shaped regions I think inpolygon would be the easiest function to use. Perhaps something like this:

theta360 = linspace(0,1,3601)*2*pi;
idx18 = 1:200:3601;
theta18 = theta360(idx18);
R = 200;
[x,y] = meshgrid(-200:200);
Im = zeros(401);
for iSeg = 1:16,                                                 
  rEdge = [r0;r_circ(idx18(iSeg+2):idx18(iSeg+3),:)];
  inP = inpolygon(x(:),y(:),rEdge(:,1),rEdge(:,2));
  Im(inP) = iSeg;
  imagesc(Im),drawnow
end

You might want to modify the angular resolution (in theta360), the number of points along the circle (idx18) and the values you assign to the pixels inside, as well as the image resolution etc.

HTH

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darova 2021-8-15

patch() will be better way than imagesc()

Moshe Peleg 2021-9-24

thank you very much for your help !

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Answer 2

darova 2021-8-15

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在 MATLAB Online 中打开

Here is an example with using matrix

r0 = 100; % radius of a circle

t = linspace(0, 2*pi, 15)+pi/2; % 15 points on a circle

[x,y] = pol2cart(t,r0); % cartesian 15 points

[X,Y] = meshgrid(-20-r0:r0+20); % mesh for an image

ii = 14;

[T,R] = cart2pol(X-x(ii),Y-y(ii)); % 15 segments in polar

t1 = cart2pol(x-x(ii),y-y(ii)); % angles of each segment

I = X*0+1;

for i = [1:length(t1)-1]

cond = t1(i) < T & T < t1(i+1); % choose segment

I = I + cond*i;

end

cond = X.^2 + Y.^2 < r0^2;

I = I.*cond; % assing zero value outside circle

surf(I,'edgecolor','none','facecolor','interp')

colormap gray

view(0,90)

axis equal

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darova 2021-8-16

Your code doesn't work

Moshe Peleg 2021-9-24

thank you very much for your help !

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Create an image (pixels) circle with slices (not from the center) and paint each slice a different color

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Create an image (pixels) circle with slices (not from the center) and paint each slice a different color

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