How can I separate the body from legs in the crab image

How to remove the legs from crab image and separate body only

Answer 1

[Image Analyst]

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".