MATLAB Answers


How to scan a gray image in inverse-s order and calculate the differences of the adjacent pixels and plot a histogram of difference matrix?

Asked by eram fatima on 15 Sep 2018 at 16:51
Latest activity Commented on by eram fatima on 16 Sep 2018 at 18:49

somebody please tell me how to do it in matlab.


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1 Answer

Answer by Image Analyst
on 15 Sep 2018 at 19:32
Edited by Image Analyst
on 15 Sep 2018 at 19:34

You can use conv2(), or graycomatrix(). You can set up a kernel defining "adjacent" then call conv() then histogram()

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;
% Read in gray scale demo image.
folder = fileparts(which('cameraman.tif')); % Determine where demo folder is (works with all versions).
baseFileName = 'cameraman.tif';
% 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);
rgbImage = 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(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.
	grayImage = rgbImage; % It's already gray scale.
% Now it's gray scale with range of 0 to 255.
% Display the image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Image', 'FontSize', fontSize, 'Interpreter', 'None');
axis('on', 'image');
hp = impixelinfo();
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);
% 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')
% Define kernel
kernel = [-1, 1];
diffImage = conv2(double(grayImage), kernel);
% Display the image.
subplot(2, 2, 2);
imshow(diffImage, []);
title('Difference Image', 'FontSize', fontSize, 'Interpreter', 'None');
axis('on', 'image');
hp = impixelinfo();
% Display the histogram
subplot(2, 2, 3:4);
grid on;
xlabel('Difference Value', 'FontSize', fontSize);
ylabel('Count', 'FontSize', fontSize);
title('Histogram of Difference Values', 'FontSize', fontSize);


Show 1 older comment

Then use the same option:

diffImage = conv2(double(grayImage), kernel, 'same');

</matlabcentral/answers/uploaded_files/132628/png.PNG> this is how i want to access the pixels...however with conv2() , the pixels are accessed row wise.

Iam attaching an image of the order in which pixels are to be accessed...

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