How to remove the gray dots from the black holes from the following image?

I have tried weiner2 filter, medfilt2 and gaussian blur also but the results are not satisfactory.

[KALYAN ACHARJYA]

Can you explain it more? If you remove the gray from the image, then image turn to complete black. Pls, share the code what you have tried so far.

Answer 1

[Image Analyst]

Try this code that removes all blobs except for the largest one:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

folder = pwd;
baseFileName = 'ceramic_4_000.bmp';
% Get the full filename, with path prepended.
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
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage);
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(grayImage);
  % 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 = grayImage(:, :, 1); % Take red channel.
end
% Display the image.
subplot(2, 3, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo;
axis('on', 'image'); % Make sure image is not artificially stretched because of screen's aspect ratio.

%------------------------------------------------------------------------------
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);
drawnow;

% Turn into a binary image.
binaryImage = imbinarize(grayImage); 

% Find all the blobs.
[labeledImage, numberOfRegions] = bwlabel(binaryImage);
fprintf('Found %d regions.\n',numberOfRegions);

% Display the binary image.
subplot(2, 3, 2);
% imhist(grayImage);
imshow(binaryImage, []);
caption = sprintf('Binary Image with %d Blobs', numberOfRegions);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo;
axis('on', 'image'); % Make sure image is not artificially stretched because of screen's aspect ratio.

% Let's assign each blob a different color to visually show the user the distinct blobs.
coloredLabels = label2rgb (labeledImage, 'hsv', 'k', 'shuffle'); % pseudo random color labels
% coloredLabels is an RGB image.  We could have applied a colormap instead (but only with R2014b and later)
subplot(2, 3, 3);
imshow(coloredLabels);
axis('on', 'image'); % Make sure image is not artificially stretched because of screen's aspect ratio.
caption = sprintf('Pseudo colored labels, from label2rgb().\nBlobs are numbered from top to bottom, then from left to right.');
title(caption, 'FontSize', fontSize);

binaryImage1 = bwareafilt(binaryImage, 1);
% Display the binary image.
subplot(2, 3, 4);
imshow(binaryImage1, []);
title('Binary Image with Islands Removed', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo;
axis('on', 'image'); % Make sure image is not artificially stretched because of screen's aspect ratio.

% Get an image of just the small blobs
smallBlobs = binaryImage & ~binaryImage1;
% Display the binary image.
subplot(2, 3, 5);
imshow(smallBlobs, []);
title('Binary Image of Islands', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo;
axis('on', 'image'); % Make sure image is not artificially stretched because of screen's aspect ratio.

% Erase the small blobs by setting them to zero in the original gray image.
grayImage(smallBlobs) = 0;
% Display the final gray image with the small gray islands replaced.
subplot(2, 3, 6);
imshow(grayImage, []);
title('Gray Image with Islands Removed', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo;
axis('on', 'image'); % Make sure image is not artificially stretched because of screen's aspect ratio.

[Image Analyst]

Well that's totally different than "remove the gray dots from the black holes". So why aren't you using medfilt2()?