How to remove unwanted small blob?

I want to remove the small blob and only keep the largest connected blob.

How can I do it?

[Tan Wen Kun]

I want the keep the region which in black box only.

Other small blob I want turn to background color

Answer 1

[Image Analyst]

First of all, don't use watershed or whatever to break up the blobs into sub-blobs. Then use imclearborder() to get rid of blobs touching the borders, then use bwareafilt(binaryImage, 1) to get just the largest blob.

[Tan Wen Kun]

so what method should I use to get the blob?

[Image Analyst]

You should use the two functions I mentioned, imclearborder() and bwareafilt().

[Tan Wen Kun]

IM = edge(im2double(rgb2gray(imread('jump.jpg'))),'canny');

figure;imshow(IM,[]);

% load IM

[r c] = size(IM);

data = IM(:);

[center,U,obj_fcn] = fcm(data,4); % Fuzzy C-means classification with 4 classes    

% Finding the pixels for each class

maxU = max(U);

index1 = find(U(1,:) == maxU);

index2 = find(U(2,:) == maxU);

index3 = find(U(3,:) == maxU);

index4 = find(U(4,:) == maxU);

% Assigning pixel to each class by giving them a specific value

fcmImage(1:length(data))=0;       

fcmImage(index1)= 1;

fcmImage(index2)= 0.66;

fcmImage(index3)= 0.33;

fcmImage(index4)= 0.0;

% Reshapeing the array to a image

imagNew = reshape(fcmImage,r,c);

figure;imshow(imagNew,[]);

gradmag = imagNew;

g = gradmag - min(gradmag(:));

g = g / max(g(:));

th = graythresh(g); %# Otsu's method.

a = imhmax(g,th/2); %# Conservatively remove local maxima.

th = graythresh(a);

b = a > th/4; %# Conservative global threshold.

c = imclose(b,ones(8)); %# Try to close contours.

d = imfill(c,'holes'); %# Not a bad segmentation by itself.

%# Use the rough segmentation to define markers.

%#g2 = imimposemin(g, ~ imdilate( bwperim(a), ones(4) ));

%#L = watershed(g2);

%#Lrgb = label2rgb(L);

%#figure;imshow(g2,[]);

g3 = imclearborder(d);

g4 = bwareafilt(g3,1);

[Tan Wen Kun]

This the example I trying.

What I want to do is to get the blob first then only remove the small blob and keep the largest blob.

If do not use watershed, I cannot get the blob and I dunno two function you give need to use at where.

[Image Analyst]

I don't have the fuzzy toolbox. Please post the (badly-named) "b" image and I'll just start from there.

[Tan Wen Kun]

I just use matlab to run. I think no need fuzzy toolbox

[Image Analyst]

Not that one. I don't want the edge image. Don't you have a binary image?

[Tan Wen Kun]

binary is c and d, b is edge image

[Image Analyst]

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
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;

fullFileName = fullfile(pwd, 'd.jpg');
grayImage = imread(fullFileName);
% Get the dimensions of the image.  
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(grayImage);
if numberOfColorBands > 1
  % It's not really gray scale like we expected - it's color.
  % Convert it to gray scale by taking only the green channel.
  grayImage = grayImage(:, :, 2); % Take green channel.
end
% Display the original gray scale image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% 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') 

% Binarize the gray scale image.
binaryImage = grayImage > 128;
subplot(2, 2, 2);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');

% Get rid of blobs touching the border
binaryImage = imclearborder(binaryImage);
subplot(2, 2, 3);
imshow(binaryImage, []);
title('With border cleared', 'FontSize', fontSize, 'Interpreter', 'None');

% Get the largest remaining blob:
binaryImage = bwareafilt(binaryImage, 1);
subplot(2, 2, 4);
imshow(binaryImage, []);
title('Largest Remaining Blob', 'FontSize', fontSize, 'Interpreter', 'None');