Overlapping coloured circles - RGB circles

Hi!

I want to overlap three coloured circles, red, green, blue, in order to form the RGB palette, like below:

So far, i have the following code and result

k = 0 : 0.001 : 2*pi;
x = cos(k)+2.3; y = sin(k)+2;
z = cos(k)+3; w = sin(k)+1;
t = cos(k)+1.5; u = sin(k)+1;
fill(x,y, 'r', EdgeColor='none'),; 
hold on 
fill(z,w, 'b', EdgeColor='none');
fill(t,u, 'g', EdgeColor='none');
grid off

But I can't make the properly overlap and make them change the colours like above. Any sugestions, please?

Thank you!

Answer 1

[Image Analyst]

Try making a digital iamge so you can add the colors. What you were doing was stcking opaque patches.

% Demo to make 3 colored primary color circles to show how you can get white, and all 6 "Primary" colors.
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;
markerSize = 40;

imageSizeX = 512;
imageSizeY = 512;
radius = 181;
distanceFromCenter = 75;

% First make the red image.
centerX = 256;
centerY = 256 - distanceFromCenter;
redImage = CreateCircleImage(imageSizeX, imageSizeY, centerX, centerY, radius);
subplot(2, 2, 1);
% Now, display it.
image(redImage);
colormap([0 0 0; 1 1 1]);
title('Red Circle', 'FontSize', fontSize);
axis('on', 'image');
% Put up crosshairs.
yline(256, 'Color', 'r', 'LineWidth', 2);
xline(256, 'Color', 'r', 'LineWidth', 2);

% Next make the green image.
centerX = 256 + distanceFromCenter * cosd(225);
centerY = 256 - distanceFromCenter * sind(225);
greenImage = CreateCircleImage(imageSizeX, imageSizeY, centerX, centerY, radius);
subplot(2, 2, 2);
% Now, display it.
image(greenImage);
colormap([0 0 0; 1 1 1]);
title('Green Circle', 'FontSize', fontSize);
axis('on', 'image');
% Put up crosshairs.
yline(256, 'Color', 'g', 'LineWidth', 2);
xline(256, 'Color', 'g', 'LineWidth', 2);

% Next make the blue image.
centerX = 256 + distanceFromCenter * cosd(-45);
centerY = 256 - distanceFromCenter * sind(-45);
blueImage = CreateCircleImage(imageSizeX, imageSizeY, centerX, centerY, radius);
subplot(2, 2, 3);
% Now, display it.
image(blueImage);
colormap([0 0 0; 1 1 1]);
title('Blue Circle', 'FontSize', fontSize);
axis('on', 'image');
% Put up crosshairs.
yline(256, 'Color', 'b', 'LineWidth', 2);
xline(256, 'Color', 'b', 'LineWidth', 2);

% Combine the 3 separate color channels into one RGB image.
rgbImage = cat(3, redImage, greenImage, blueImage);

% If you want the surround to be white instead of black, do this:
mask = 255 * uint8(redImage == 0 & greenImage == 0 & blueImage == 0);
rgbImage = rgbImage + cat(3, mask, mask, mask);

subplot(2, 2, 4);
imshow(rgbImage);
title('All Colors', 'FontSize', fontSize);
axis('on', 'image');
% Put up red crosshairs
% yline(256, 'Color', 'r', 'LineWidth', 2);
% xline(256, 'Color', 'r', 'LineWidth', 2);
g = gcf;
g.WindowState = 'maximized';

%================================================================================================
function circlePixels = CreateCircleImage(imageSizeX, imageSizeY, centerX, centerY, radius)
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Convert to a uint8 image
circlePixels = uint8(circlePixels) * uint8(255);
end

[Carmen Chira]

Thank you!

Answer 2

[DGM]

This creates an image:

sz = [512 512]; % image size
cim = sz.*[0.46 0.5]; % [y x] center of image
r = mean(sz)/4; % radius of circle
Pth = [90 210 330]; % position angle
Pr = r*2/3; % position radius

% calculate circle locations
cx = Pr*cosd(Pth) + cim(2);
cy = sz(1)-(Pr*sind(Pth) + cim(1));

% draw circles in an RGB image
outpict = zeros(sz);
for k = 1:numel(Pth)
    outpict(:,:,k) = drawcircle(sz,[cy(k) cx(k)],r);
end

% show the result
imshow(outpict)

% draw circle with smooth edges
function circ = drawcircle(sz,c,r)
    xx = 1:sz(2);
    yy = (1:sz(1)).';
    circ = sqrt((xx-c(2)).^2 + (yy-c(1)).^2);
    circ = min(max((r-circ)/2,0),1);
end

I'm sure there are plenty of other ways.

[Carmen Chira]

Thank you!