Sliding pixel window to get 8 neighbour pixel values

Hi, Can anyone plz tell me how to slide a filter window of 3*3 over the pixels of an image one by one and get the 8 neighbouring pixel values.

[Jan]

What do you wnt to do with the 8 neighboring pixles? With "getting" the problem is not solve, is it?

[Adam Danz]

What do you plan to do with the 3x3 windows?

[thorati chiranjeevi]

Hi @Jan@Adam Danz, I want to give these pixel values as input to Fuzzy logic controller

[Adam Danz]

Is the 3X3 window sliding by 1 unit or like a boxcar, by 3 units?

Sliding rightward then downward starting from the top left corner?

Lots of time spent here on missing details.

[thorati chiranjeevi]

@Adam Danz It has to pass from top left corner like a boxcar by 3 units and cover the entire image. sorry for the inconvenience as i am very new to this MATLAB.

Answer 1

[Adam Danz]

Here's the framework to get you started.

An image is displayed and the starting and end coordinates of each 4x3 (width x height) window is stored in table T. The window moves horizontally across the image and then downward.

Using a for-loop, each window is plotted and the uint8 color values are printed in each pixel which can be compared to the colorbar to confirm accuracy. Don't try this with a large image where pixel sizes are a lot smaller.

The variable Isection contains the section of values from image I within the window.

% Load and display demo image
I =  imread('cameraman.tif');
I = I(60:88, 130:157);
fig = figure('WindowState','maximized'); 
imagesc(I)
colormap('gray')
axis equal
axis tight
hold on
colorbar()

% Get end points (lower right corner) of each window
% stored in (end_x, end_y).
windowSize = [4,3]; % width, height
rowIndex = windowSize(2):windowSize(2):size(I,1); 
columnIndex = windowSize(1):windowSize(1):size(I,2); 
[end_x, end_y] = ndgrid(columnIndex, rowIndex);

% Get the start point (upper left corner) of each window
% stored in (start_x, start_y).
start_x = end_x - windowSize(1) + 1; 
start_y = end_y - windowSize(2) + 1;

% Put window coordinates into a table for easier viewing.
T = table(start_x(:), end_x(:), start_y(:), end_y(:), ...
    'VariableNames', {'X0', 'X1', 'Y0', 'Y1'})

% loop through each window
for i = 1:numel(start_x)
    % Extract image data within window
    Isection = I(T.Y0(i):T.Y1(i),T.X0(i):T.X1(i));
    
    % Show window
    rectangle('position',[T.X0(i)-.5, T.Y0(i)-.5, windowSize],'EdgeColor','r','LineWidth',1)
    
    % Show color values
    [y,x] = ndgrid(T.Y0(i):T.Y1(i), T.X0(i):T.X1(i));
    text(x(:), y(:), compose('%d',Isection(:)), 'VerticalAlignment', 'middle', 'HorizontalAlignment', 'center', 'FontSize', 9, 'Color', 'c')
    
    drawnow
    pause(.2)
end

To group the data without showing the animation, replace the for-loop above with this version below. Iboxcar is an NxMxJ array for window size NxM for J windows. So data in the 2nd window in the animation is stored in Iboxcar(:,:,2).

Iboxcar = nan(windowSize(2),windowSize(1),numel(start_x));
for i = 1:numel(start_x)
    % Extract image data within window
    Iboxcar(:,:,i) = I(T.Y0(i):T.Y1(i),T.X0(i):T.X1(i));
end

[thorati chiranjeevi]

Thank you @Adam Danz

[Sparsh Garg]

Hey @Adam Danz thanks for the code it's really helpful but I have noticed that it is extremely slow.Any ideas on how we can speed it up

[Walter Roberson]

It is a demonstration, that is deliberately drawing lots of things on the screen for visual purposes. You could reduce the pause(.2) to pause() of a smaller number, but you are still left with drawing a lot of things on the screen. How quickly could you read the changing display?

[Adam Danz]

@Sparsh Garg, to avoid the visual animation and collect just group the data into varible, replace the loop in my answer with this loop. This takes less than 20 ms.

Iboxcar = nan(windowSize(2),windowSize(1),numel(start_x));
for i = 1:numel(start_x)
    % Extract image data within window
    Iboxcar(:,:,i) = I(T.Y0(i):T.Y1(i),T.X0(i):T.X1(i));
end

Iboxcar is an NxMxJ array for window size NxM and J windows. So data in the 2nd window in the animation is stored in Iboxcar(:,:,2).

I'll update my answer to include this option.

Answer 2

[Walter Roberson]

https://www.mathworks.com/help/images/ref/nlfilter.html

[thorati chiranjeevi]

my image size is [562 649] can you please provide the code. Thanks.

[Adam Danz]

Looking briefly at nlfilter.m, the filtering is done by a sliding window by 1 unit rather than acting as a boxcar filter that slides by the width/height of the window.

> can you please provide the code

@thorati chiranjeevi, it's unlikely that someone's going to volunteer to do your work for you. Some questions are specific and providing code is the best way to answer them. Your question does not point to a specific problem so the responses you'll likely get are ones that will point you in the right direction.