deleting leadind and trail zeros in an image

Hi all I am working on enhancing a grayscal images, the first step should be cropping the image by removing lead and trail zeros (zeros rows an columns surrounding the image). i want t remove the surrounding zeros. please be advised that the cropping has be applied on zeros rows and columns that surrounding the image for different images, so i need a function or an algorithm does this cropping on different images. thanks in advance

Answer 1

[Image Analyst]

Try this:

mask = grayImage ~= 0; % Find all zeros, even those inside the image.
mask = imfill(mask, 'holes'); % Get rid of zeros inside image.
% Invert mask and get bounding box.
props = regionprops(~mask, 'BoundingBox');
% Crop image.
croppedImage = imcrop(grayImage, props.BoundingBox);

[Hassan Qassim]

Hello, Thanks for replying unfortunately it didnt work, zeros still there

[Image Analyst]

It was off the top of my head. You forgot to attach your image to allow me to help you. I'll check back later for it.

[Image Analyst]

Try this:

grayImage = imread('cameraman.tif');
grayImage = padarray(grayImage, [50, 50]);
subplot(2,2,1);
imshow(grayImage);
mask = grayImage ~= 0; % Find all zeros, even those inside the image.
mask = imfill(mask, 'holes'); % Get rid of zeros inside image.
subplot(2,2,2);
imshow(mask);
% Get bounding box.
props = regionprops(mask, 'BoundingBox');
boundingBox = ceil(props.BoundingBox)
boundingBox(3) = boundingBox(3)-1;
boundingBox(4) = boundingBox(4)-1;
% Crop image.
croppedImage = imcrop(grayImage, boundingBox);
subplot(2,2,3);
imshow(croppedImage);

[Hassan Qassim]

Dear My Friend thanks a lot for your help, your efforts are really appreciated. please have a look at attached image, i want to crop it as indicated in red rectangle. i am only interested in the part inside the red rectangle. looking forward for your answer. thanks in advance

[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 short g;
format compact;
fontSize = 25;

%===============================================================================
% Get the name of the image the user wants to use.
baseFileName = 'test1-paint.jpg';
% Get the full filename, with path prepended.
folder = pwd
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.
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(:, :, 2); % Take green channel.
end

% Display the original image.
subplot(2, 2, 1);
imshow(grayImage, []);
axis on;
caption = sprintf('Original Color Image, %s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.

% 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')

% Find the white surround.
whiteSurround = grayImage > 245;
% Take the largest blob only.
whiteSurround = bwareafilt(whiteSurround, 1);

% Display the image.
subplot(2, 2, 2);
imshow(whiteSurround, []);
axis on;
caption = sprintf('White Surround Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;

% Erase image where there is the white surround.
grayImage(whiteSurround) = 0;

% Find the non-black pixels.
mask = grayImage > 7;

% Take the largest blob only.
mask = bwareafilt(mask, 1);
% Display the image.
subplot(2, 2, 3);
imshow(mask, []);
axis on;
caption = sprintf('Mask Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;

% Find the bounding box
props = regionprops(mask, 'BoundingBox');
% Crop the image to the bounding box.
croppedImage = imcrop(grayImage, props.BoundingBox);
% Display the image.
subplot(2, 2, 4);
imshow(croppedImage, []);
axis on;
caption = sprintf('Cropped Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;

[Hassan Qassim]

thanks a lot my dear friend. that worked very well. your information were very clear and very helpful. thanks again

[Imran Riaz]

I tried this code, but the output is not same as u shared the output. I also need to remove the black area of my masked images but cannot do that. Can you help me?

[Image Analyst]

@Imran Riaz I just copied the code and ran it on test1_paint.jpg and got exactly the output I posted below it. You must have changed something. Post your new image in a new question and we'll help.

Note I cropped the image - I did not mask it. I did not get a mask of "black" areas. Not sure what black pixels you want to remove but keep in mind that the image must remain rectangular. We can't have images with irregularly-shaped borders.

[Imran Riaz]

My image have different dimensions, I think that is the mistake. I am also attaching the image here.