Crop a circle from an image and put it on another image

Question

Ali Purse 2018-10-27

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评论： Anand Ra 2022-11-18

May you please help me how to crop (cut) a circle from an image and put it on another image?

I know that I can crop a circle from an image using following code:

I = imread('patricia.jpg');
imageSize = size(I);
ci = [250, 300, 100];     % center and radius of circle ([c_row, c_col, r])
[xx,yy] = ndgrid((1:imageSize(1))-ci(1),(1:imageSize(2))-ci(2));
mask = uint8((xx.^2 + yy.^2)<ci(3)^2);
croppedImage = uint8(zeros(size(I)));
croppedImage(:,:,1) = I(:,:,1).*mask;
croppedImage(:,:,2) = I(:,:,2).*mask;
croppedImage(:,:,3) = I(:,:,3).*mask;
imshow(croppedImage);

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Answer 1

jonas 2018-10-27

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编辑：jonas 2018-10-27

在 MATLAB Online 中打开

You were almost there, and given the error message I think you could have figured it out :)

"Integers can only be combined with integers of the same class, or scalar doubles."

croppedImage(:,:,1) = I(:,:,1).*uint8(mask);
croppedImage(:,:,2) = I(:,:,2).*uint8(mask);
croppedImage(:,:,3) = I(:,:,3).*uint8(mask);

Here is a bonus method with inpolygon if you want to crop arbitrary shapes:

% Load image
RGB = imread('peppers.png');
%Convert to 2D to create mask
GRAY = rgb2gray(RGB);
imageSize = size(GRAY);
ci = [250, 300, 100];     % center and radius of circle ([c_row, c_col, r])
%Create circle
h = viscircles(ci(1:2),ci(3));
c = h.Children(1).XData(1:end-1);
r = h.Children(2).YData(1:end-1);
% Create grid for mask
[C,R] = meshgrid(1:imageSize(2),1:imageSize(1));
%Find pts inside of circle
mask = inpolygon(R,C,r,c);
%Crop
croppedImage = uint8(zeros(imageSize));
croppedImage(:,:,1) = RGB(:,:,1).*uint8(mask);
croppedImage(:,:,2) = RGB(:,:,2).*uint8(mask);
croppedImage(:,:,3) = RGB(:,:,3).*uint8(mask);
imshow(croppedImage);

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Answer 2

Image Analyst 2018-10-27

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在 MATLAB Online 中打开

Try this to copy a circular mask/roi region from image 1 and then paste it onto the same location of image 2:

% Read first image.
rgbImage1 = imread('peppers.png');
[rows, columns, numberOfColorChannels] = size(rgbImage1);
subplot(2, 2, 1);
imshow(rgbImage1);
axis('on', 'image');
title('rgbImage1', 'FontSize', 20);
% Get the second image - should be the same size as rgbImage1.
rgbImage2 = imread('coloredChips.png');
rgbImage2 = imresize(rgbImage2, [rows, columns]);
subplot(2, 2, 2);
imshow(rgbImage2);
axis('on', 'image');
title('rgbImage2', 'FontSize', 20);
% Make the circle mask.
imageSize = size(rgbImage1);
ci = [250, 300, 100];     % center and radius of circle ([c_row, c_col, r])
[xx,yy] = ndgrid((1:imageSize(1))-ci(1),(1:imageSize(2))-ci(2));
mask = (xx.^2 + yy.^2) < ci(3)^2;
subplot(2, 2, 3);
imshow(mask);
axis('on', 'image');
title('Mask', 'FontSize', 20);
% Get the individual color channels
% Extract the individual red, green, and blue color channels.
redChannel1 = rgbImage1(:, :, 1);
greenChannel1 = rgbImage1(:, :, 2);
blueChannel1 = rgbImage1(:, :, 3);
% For the second one, let's use the new imsplit(). 
% It's in R2018b.  If you don't have it, use code like the above.
[redChannel2, greenChannel2, blueChannel2] = imsplit(rgbImage2);
% Paste the image from the circle region of rgbImage1 onto rgbImage2 in just the circle region.
redChannel2(mask) = redChannel1(mask);
greenChannel2(mask) = greenChannel1(mask);
blueChannel2(mask) = blueChannel1(mask);
% Recombine separate color channels into a single, true color RGB image.
rgbImage2 = cat(3, redChannel2, greenChannel2, blueChannel2);
% Display it.
subplot(2, 2, 4);
imshow(rgbImage2);
axis('on', 'image');
title('Image 1 pasted onto image 2 only within mask', 'FontSize', 20);

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Image Analyst 2022-11-17

在 MATLAB Online 中打开

Oh, in your last announcement you didn't actually ask anything. I'm sure you can just make a loop to loop 50 times and place circles onto the mask, right? Try it, I have confidence in you. In case you just can't figure it out, I did it for you (depriving you of all the fun) for 10 circles at random locations:

% Demo by Image Analyst
% Initialization Steps.
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 = 18;
% Read first image.
rgbImage1 = imread('peppers.png');
[rows, columns, numberOfColorChannels] = size(rgbImage1);
subplot(2, 2, 1);
imshow(rgbImage1);
axis('on', 'image');
title('rgbImage1', 'FontSize', 20);
% Get the second image - should be the same size as rgbImage1.
rgbImage2 = imread('coloredChips.png');
rgbImage2 = imresize(rgbImage2, [rows, columns]);
subplot(2, 2, 2);
imshow(rgbImage2);
axis('on', 'image');
title('rgbImage2', 'FontSize', 20);
% Make a mask of all the circles
numCircles = 10; % Whatever you want.
mask = false(rows, columns);
radius = 30;
for k = 1 : numCircles
    % Get the center.
    xCenter = round(radius + (columns - 2 * radius) * rand(1));
    yCenter = round(radius + (rows - 2 * radius) * rand(1));
    % Make the circle mask.
    [xx, yy] = ndgrid((1:rows)-yCenter, (1:columns)-xCenter);
    thisMask = (xx.^2 + yy.^2) < radius ^ 2;
    % Combine this mask with the master mask.
    mask  = mask | thisMask;
end
subplot(2, 2, 3);
imshow(mask);
axis('on', 'image');
caption = sprintf('Mask with %d circles', numCircles);
title(caption, 'FontSize', 20);
% Get the individual color channels
% Extract the individual red, green, and blue color channels.
redChannel1 = rgbImage1(:, :, 1);
greenChannel1 = rgbImage1(:, :, 2);
blueChannel1 = rgbImage1(:, :, 3);
% For the second one, let's use the new imsplit().
% It's in R2018b.  If you don't have it, use code like the above.
[redChannel2, greenChannel2, blueChannel2] = imsplit(rgbImage2);
% Paste the image from the circle region of rgbImage1 onto rgbImage2 in just the circle region.
redChannel2(mask) = redChannel1(mask);
greenChannel2(mask) = greenChannel1(mask);
blueChannel2(mask) = blueChannel1(mask);
% Recombine separate color channels into a single, true color RGB image.
rgbImage2 = cat(3, redChannel2, greenChannel2, blueChannel2);
% Display it.
subplot(2, 2, 4);
imshow(rgbImage2);
axis('on', 'image');
title('Image 1 pasted onto image 2 only within mask', 'FontSize', 20);

Image Analyst 2022-11-18

编辑：Image Analyst 2022-11-18

Sure, try it! Just get a coordinate of one circle in the input and another coordinate in the output image. Just do one circle at a time instead of all 50 at once. Start a new question if you still need help.

Anand Ra 2022-11-18

@Image Analyst

Got it. Thanks for the tip, was able to do it. Very much appreciate the help.

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Crop a circle from an image and put it on another image

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