Take the Euclidean distance transform, threshold it, then use it as a mask. 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 = 'crab.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, 3, 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, 3, 2);
imshow(grayImage, []);
axis on;
title('Gray Image', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;
% Display the histogram of the image.
subplot(2, 3, 3);
histogram(grayImage, 256);
title('Histogram of Gray Image', 'FontSize', fontSize, 'Interpreter', 'None');
grid on;
drawnow;
%=======================================================================================
binaryImage = grayImage < 240;
% Keep only the largest blob.
binaryImage = bwareafilt(binaryImage, 1);
% Display the masked image.
subplot(2, 3, 3);
imshow(binaryImage, []);
axis on;
title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;
% Compute the Euclidean Distance Transform
edtImage = bwdist(~binaryImage);
% Display the image.
subplot(2, 3, 4);
imshow(edtImage, []);
axis on;
title('Distance Transform Image', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;
% Get a new mask
mask = edtImage > 18;
% Take only the largest blob, representing the main body of the animal.
mask = bwareafilt(mask, 1);
% Display the image.
subplot(2, 3, 5);
imshow(mask, []);
axis on;
title('Mask', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;
% Use the mask to mask the original image to white outside the main body.
grayImage(~mask) = 255;
% Display the final image.
subplot(2, 3, 6);
imshow(grayImage, []);
axis on;
title('Masked Image', 'FontSize', fontSize, 'Interpreter', 'None');
If you want, you could smooth the mask outline so it's not quite so "pointy".
