how to draw circle in an image?

Hello Everyone

I am currently working on the project of object recognition using matlab. but i am not getting how to draw circle with specific radius on specific image. i had calculated the centroid of the image, and using these as my center point i want to draw circle. please assist me.

Thanks

[Benjamin Drewry]

try using viscircles https://www.mathworks.com/help/images/ref/viscircles.html

Answer 1

[kittu]

you can draw the circle using the following code:

%e
%r= desired radius
%x = x coordinates of the centroid
%y = y coordinates of the centroid
th = 0:pi/50:2*pi;
xunit = r * cos(th) + x;
yunit = r * sin(th) + y;
h = plot(xunit, yunit);

[manish meena]

thank you for your help

Answer 2

[Matthew Eicholtz]

In case someone else stumbles upon this question like I did and is unsatisfied with the current answers, I have found that insertShape is a useful function for adding rasterized shapes to an image. Note that this requires the Computer Vision System Toolbox.

help insertShape

Answer 3

[Image Analyst]

See my demo. It does that. It will just require slight modifications to turn the ellipse into a circle (because there's an imellipse but no imcircle function so you can use bwperim if you want the outline), and to make the circle an outline rather than a solid (if that's what you want, but you didn't make that clear).

% Demo to write an ellipse and a line into the overlay of an image,
% and then to burn those overlays into the image.

%----- Initializing steps -----
% Clean up
clc;
clear all;
close all;
workspace; % Display the workspace panel.

hasIPT = license('test', 'image_toolbox');
if ~hasIPT
  % User does not have the toolbox installed.
  message = sprintf('Sorry, but you do not seem to have the Image Processing Toolbox.\nDo you want to try to continue anyway?');
  reply = questdlg(message, 'Toolbox missing', 'Yes', 'No', 'Yes');
  if strcmpi(reply, 'No')
    % User said No, so exit.
    return;
  end
end

% Display images to prepare for the demo.
monochromeImage = imread('pout.tif');
subplot(2, 4, 1);
imshow(monochromeImage);
title('Original Image');
subplot(2, 4, 2);
imshow(monochromeImage);
title('Original Image with ellipse in overlay');
subplot(2, 4, 5);
imshow(monochromeImage);
title('Original Image');
subplot(2, 4, 6);
imshow(monochromeImage);
title('Original Image with line in overlay');
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure.
set(gcf,'name','Image Analysis Demo','numbertitle','off') 

%----- Burn ellipse into image -----
% Create elliptical mask, h, as an ROI object over the second image.
subplot(2, 4, 2);
hEllipse = imellipse(gca,[10 10 50 150]); % Second argument defines ellipse shape and position.
% Create a binary image ("mask") from the ROI object.
binaryImage = hEllipse.createMask();
% Display the ellipse mask.
subplot(2, 4, 3);
imshow(binaryImage);
title('Binary mask of the ellipse');
% Let's try to add some text.  (Doesn't work)
% hText = text(50, 100, 'Line of Text');
% textMask = hText.createMask();
% binaryImage = binaryImage & textMask;
% imshow(binaryImage);
% Burn ellipse into image by setting it to 255 wherever the mask is true.
monochromeImage(binaryImage) = 255;
% Display the image with the "burned in" ellipse.
subplot(2, 4, 4);
imshow(monochromeImage);
title('New image with ellipse burned into image');

%----- Burn line into image -----
burnedImage = imread('pout.tif');
% Create line mask, h, as an ROI object over the second image in the bottom row.
subplot(2, 4, 6);
hLine = imline(gca,[10 100],[10 100]); % Second argument defines line endpoints.
% Create a binary image ("mask") from the ROI object.
binaryImage2 = hLine.createMask();
% Display the line mask.
subplot(2, 4, 7);
imshow(binaryImage2);
title('Binary mask of the line');
% Burn line into image by setting it to 255 wherever the mask is true.
burnedImage(binaryImage2) = 255;
% Display the image with the "burned in" line.
subplot(2, 4, 8);
imshow(burnedImage);
title('New image with line burned into image');

Answer 4

[Walter Roberson]

See the FAQ. http://matlabwiki.mathworks.com/MATLAB_FAQ

Answer 5

[Matt J]

See also imellipse()

Answer 6

[DGM]

As of R2018b, this can be done interactively using ROI tools: drawcircle() drawellipse(), and createMask().

Alternatively, if you want a simple antialiased circle, that's a different story.

% let's say you have an image 
inpict = imread('peppers.png'); % uint8 (RGB)
sz = size(inpict);

% create a mask with a circle
r = 125;
c = [100 100]; % [y x]
mask = drawaacircle(sz(1:2),c,r);

% use the mask to set the color in the target image
fgcolor = [1 0.7 0];
outpict = mask.*reshape(fgcolor,1,1,[]) + (1-mask).*im2double(inpict);
outpict = im2uint8(outpict);

% do it again, but make the circle semitransparent purple
% create a mask with a circle
r = 100;
c = [300 400]; % [y x]
mask = drawaacircle(sz(1:2),c,r);
mask = 0.5*mask; % 50% opacity

% use the mask to set the color in the target image
fgcolor = [0.7 0.3 1];
outpict = mask.*reshape(fgcolor,1,1,[]) + (1-mask).*im2double(outpict);
outpict = im2uint8(outpict);

% display the result
imshow(outpict)

% create a crude antialiased circle mask
function circ = drawaacircle(sz,c,r)
    xx = 1:sz(2);
    yy = (1:sz(1)).';
    circ = sqrt((xx-c(2)).^2 + (yy-c(1)).^2);
    circ = min(max(-(circ-r)/2,0),1);
end