# How do I draw overlapping circles wich change color?

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Severin Stoop on 11 Jul 2020
Answered: DGM on 24 Apr 2022 It shoul look like this

Image Analyst on 11 Jul 2020
You can just create an rgb image, and write each circle into the color plane of your choice
redChannel = 255 * ones(rows, columns, 'uint8');
greenChannel = 255 * ones(rows, columns, 'uint8');
blueChannel = 255 * ones(rows, columns, 'uint8');
% Now write the circles into whatever color channel you want.
% Use the FAQ https://matlab.fandom.com/wiki/FAQ#How_do_I_create_a_circle.3F
% Then concatenate them into an RGB image
rgbImage = cat(3, redChannel, greenChannel, blueChannel);

DGM on 24 Apr 2022
Here's one way:
% image setup
sz = [600 600]; % image size
cim = sz/2; % [y x] center of image
r1 = 100; % radius of small circle
r2 = 150; % radius of large circle
% object positions (small circles)
Pth = [0 90 180 270]; % position angle
Pr = 150; % position radius
cx = Pr*cosd(Pth) + cim(2);
cy = sz(1)-(Pr*sind(Pth) + cim(1));
% create color layers
B = ones(sz);
for k = 1:numel(Pth)
B = B - drawhardcirc(sz,[cy(k) cx(k)],r1);
end
R = 1-drawhardcirc(sz,cim,r2);
G = 1-xor(R,B);
% note that we're working with complements,since the background is white
% the four small circles are negative features in B, not R
% the large circle is a negative feature in R, not B
imshow([R G B]) outpict = cat(3,R,G,B);
imshow(outpict) % draw circle
function circ = drawhardcirc(sz,c,r)
xx = 1:sz(2);
yy = (1:sz(1)).';
circ = sqrt((xx-c(2)).^2 + (yy-c(1)).^2);
circ = circ <= r;
end