How to make circular black frame in image?

Hi, I'm trying to make a circular black frame on an image in matlab. I have figured out how to make a rectangular frame, but I can't figure how to make a circular frame. Heres the code:

im = imread('michelle_pf.jpeg'); 
imshow(im)                      
[h,w,kanaler] = size(im);       
im_k = im(1:min(h,w),1:min(h,w),:); 
figure(2),clf                   
imshow(im_k)                    
[h,w,kanaler] = size(im_k);     
im_g = rgb2gray(im_k);          
im_d = im2double(im_g);         
storleik_ramme = 50;            
for i=1:h                       
 for j=1:w                    

       if i<storleik_ramme || j<storleik_ramme || j>w-storleik_ramme || i>h-storleik_ramme 
          im_d(i,j)=0.0;        
       end
   end
end
figure(3),clf
imshow(im_d)

Answer 1

[Image Analyst]

See my demo. It's not really so complicated. I basically just fancied up the short snippet in the FAQ. http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F So, just copy, paste, and run.

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.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;

% Read in a standard MATLAB color demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'peppers.png';
% 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);

% Display the original image.
subplot(2, 2, 1);
imshow(rgbImage);
title('Original Color Image', 'FontSize', fontSize);
[rows columns numberOfColorChannels] = size(rgbImage);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);

% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
[columnsInImage rowsInImage] = meshgrid(1:columns, 1:rows);
% Next create the circle in the center of the image.
centerX = columns/2;
centerY = rows/2;
radius = min([rows columns]) / 2;
circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.

% Now, display it.
subplot(2, 2, 2);
imshow(circlePixels, []);
colormap([0 0 0; 1 1 1]);
title('Binary image of a circle', 'FontSize', fontSize);

% Mask the image.
maskedRgbImage = bsxfun(@times, rgbImage, cast(circlePixels, class(rgbImage)));

% Now, display it.
subplot(2, 2, 3);
imshow(maskedRgbImage);
title('Image Masked by the Circle', 'FontSize', fontSize);

% Mask the image the other way.
maskedRgbImage = bsxfun(@times, rgbImage, cast(~circlePixels, class(rgbImage)));

% Now, display it.
subplot(2, 2, 4);
imshow(maskedRgbImage);
title('Image Masked by the Circle', 'FontSize', fontSize);