MATLAB: How to crop circle from an image

circlescropimageImage Processing Toolboxmask by a circle or other shapeviscircles

Here I have have defined a circle using viscircles. Now i want to get the image inside the circle. How can I do that? I have tried it with impolygon but I have to crop the image for all the image in folder and turns out its really slow. Is there any way to do that?

im = imread('flower.jpg');
imshow(im);
[x,y] = getpts;
j = viscircles([x(1),y(2)], sqrt((x(1)-x(2))^2+(y(1)-y(2))^2));

Best Answer

To process a sequence of images, see the code in the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

To crop the circle from the image, use drawcircle():

% Demo to have the user click and draw a circle over an image, then blacken outside the circle and crop out the circular portion into a new image.
clc;    % Clear the command window.
fprintf('Beginning to run %s.m ...\n', mfilename);
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing
fontSize = 15;
% Get image.
originalImage = imread('peppers.png');
[rows, columns, numberOfColorChannels] = size(originalImage)
subplot(2, 2, 1);
imshow(originalImage);
axis('on', 'image');
title('Original Image', 'FontSize', fontSize);
% Maximize the window to make it easier to draw.
g = gcf;
g.WindowState = 'maximized'
% Ask user to draw a circle:
uiwait(helpdlg('Please click and drag out a circle.'));
h.Radius = 0;
while h.Radius == 0
	h = drawcircle('Color','k','FaceAlpha',0.4)
	if h.Radius == 0
		uiwait(helpdlg('You double-clicked.  You need to single click, then drag, then single click again.'));
	end
end
% Get coordinates of the circle.
angles = linspace(0, 2*pi, 10000);
x = cos(angles) * h.Radius + h.Center(1);
y = sin(angles) * h.Radius + h.Center(2);
% Show circle over image.
subplot(2, 2, 2);
imshow(originalImage);
axis('on', 'image');
hold on;
plot(x, y, 'r-', 'LineWidth', 2);
title('Original image with circle mask overlaid', 'FontSize', fontSize);
% Get a mask of the circle
mask = poly2mask(x, y, rows, columns);
subplot(2, 2, 3);
imshow(mask);
axis('on', 'image');
title('Circle Mask', 'FontSize', fontSize);
% Mask the image with the circle.
if numberOfColorChannels == 1
	maskedImage = originalImage; % Initialize with the entire image.
	maskedImage(~circleImage) = 0; % Zero image outside the circle mask.
else
	% Mask the image.
	maskedImage = bsxfun(@times, originalImage, cast(mask, class(originalImage)));
end
% Crop the image to the bounding box.
props = regionprops(mask, 'BoundingBox');
maskedImage = imcrop(maskedImage, props.BoundingBox);
% Display it in the lower right plot.
subplot(2, 2, 4);
imshow(maskedImage, []);
% Change imshow to image() if you don't have the Image Processing Toolbox.
title('Image masked with the circle', 'FontSize', fontSize);
fprintf('Done running %s.m ...\n', mfilename);

Related Solutions

MATLAB: Crop dark area and display the face only

Convert to grayscale and then threshold and find the bounding box

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
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;
% Read in the color image.
folder = pwd;
baseFileName = 'm2.bmp';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
  % Didn't find it there.  Check the search path for it.
  fullFileName = baseFileName; % No path this time.
  if ~exist(fullFileName, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
rgbImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 3.
[rows, columns, numberOfColorBands] = size(rgbImage);
% Display the original color image.
subplot(2, 3, 1);
imshow(rgbImage, []);
axis on;
title('Original Color Image', 'FontSize', fontSize);
drawnow;
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Histogram the red channel, but there is a huge spike at 255 so let's not count those.
subplot(2, 3, 2);
grayImage = rgb2gray(rgbImage);
imshow(grayImage, []);
title('Gray Scale version', 'FontSize', fontSize);
subplot(2, 3, 3);
histogram(grayImage(grayImage<255))
grid on;
title('Histogram of Gray Scale Image', 'FontSize', fontSize);
someThresholdValue = 150;
binaryImage = grayImage > someThresholdValue;
% Take largest blob
binaryImage = bwareafilt(binaryImage, 1);
subplot(2, 3, 4);
imshow(binaryImage);
grid on;
title('Binary Image', 'FontSize', fontSize);
% Label the binary image.
labeledImage = bwlabel(binaryImage);
props = regionprops(labeledImage, 'BoundingBox');
bbox = props.BoundingBox
croppedImageRGB = imcrop(rgbImage, bbox);
subplot(2, 3, 5);
imshow(croppedImageRGB);
grid on;
title('Cropped RGB Image', 'FontSize', fontSize);
% Gray scale version of cropped image
croppedImageGray = imcrop(grayImage, bbox);
subplot(2, 3, 6);
imshow(croppedImageGray);
grid on;
title('Cropped Gray Scale Image', 'FontSize', fontSize);

MATLAB: How to find the height and width of an object

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 25;
%===============================================================================
% Get the name of the first image the user wants to use.
baseFileName = 'A.jpg';
folder = fileparts(which(baseFileName)); % Determine where demo folder is (works with all versions).
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
  % The file doesn't exist -- didn't find it there in that folder.
  % Check the entire search path (other folders) for the file by stripping off the folder.
  fullFileNameOnSearchPath = baseFileName; % No path this time.
  if ~exist(fullFileNameOnSearchPath, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
%=======================================================================================

% Read in demo image.
rgbImage = imread(fullFileName);
% Get the dimensions of the image.
[rows, columns, numberOfColorChannels] = size(rgbImage);
% Display the original image.

subplot(2, 2, 1);
imshow(rgbImage, []);
axis on;
caption = sprintf('Original Color Image, %s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
[rows, columns, numberOfColorChannels] = size(rgbImage)
if numberOfColorChannels > 1
  % It's not really gray scale like we expected - it's color.
  % Use weighted sum of ALL channels to create a gray scale image.
%   grayImage = rgb2gray(rgbImage);
  % ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
  % which in a typical snapshot will be the least noisy channel.
  grayImage = rgbImage(:, :, 1); % Take red channel.
end
% Display the image.
subplot(2, 2, 2);
imshow(grayImage, []);
axis on;
caption = sprintf('Gray Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;
% Display the histogram of the image.
subplot(2, 2, 3);
histogram(grayImage, 256);
caption = sprintf('Histogram of Gray Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
grid on;
drawnow;
%=======================================================================================
binaryImage = grayImage < 150;
% Keep only the largest blob.
binaryImage = bwareafilt(binaryImage, 1);
% Display the masked image.
subplot(2, 2, 3);
imshow(binaryImage, []);
axis on;
caption = sprintf('Binary Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;
% Get the bounding box of the blob.
props = regionprops(binaryImage, 'BoundingBox');
boundingBox = [props.BoundingBox]
% Display the original image.
subplot(2, 2, 4);
imshow(rgbImage, []);
axis on;
caption = sprintf('Original Color Image, %s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
% Plot the bounding box over it.
hold on;
rectangle('Position', boundingBox, 'LineWidth', 2, 'EdgeColor', 'r')

Best Answer

Related Solutions

MATLAB: Crop dark area and display the face only

MATLAB: How to find the height and width of an object

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