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
Latest activity Commented on by eram fatima on 16 Sep 2018
somebody please tell me how to do it in matlab.


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1 Answer

Answer by Image Analyst
on 15 Sep 2018
Edited by Image Analyst
on 15 Sep 2018

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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