How to implement a function to apply the 3x3 average filter to a gray-scale image.

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amy elmossly 2012-11-14

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https://ww2.mathworks.cn/matlabcentral/answers/53657-how-to-implement-a-function-to-apply-the-3x3-average-filter-to-a-gray-scale-image

编辑： DGM 2022-11-27

采纳的回答： Image Analyst

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Here is my code

function AverageFilter(image)
I = imread(image);
[x,y] = size(I);
for i = 2:x-1
    for j = 2:y-1
        sum = 0;
        for ii = i-1:i+1  
            for jj = j-1:j+1
                sum = sum + I(ii,jj);
            end
        end
        I2(i,j) = ceil(sum/9);
    end
end
imshow(I2);

it keeps giving me the following error: Warning: Image is too big to fit on screen; displaying at 67% > In imuitools\private\initSize at 73 In imshow at 264 In AverageFilter at 18

and the resulting image is very dark..

I want to know what did i do wrong in my code and to fix this error?!!!

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justin gat 2021-5-30

sir actually what i need is this can u help me with the code sir

sir can u please send me code for this

i am considering 3x3 size window
i am taking the average of the pixels conditons are

- if the pixel values in the window is greater than 255 then i am averaging the pixels expect 255 value pixels

- if the pixel values are less than 255 value pixels then i am taking 255 as my answer

example lets take in a 3x3 window i have 5 number of 255 pixel value and 4 number less than 255 values then 255 > 254 or any other pixel value so i am keeping 255 as same if 255< 254 or any other pixel values then i am averaging all the pixels except 255 pixel value

3. after this i have to replace the pixel value by resultent value

anyone can write code for this please as soon as possible

sir I need to ignore high intensity pixel 255 and have to average all other pixels in the 3x3 window If all the pixels are white that is high intensity pixels 255 then I have keep it as 255 - sir here is the condition 1. While sliding a 3x3 window on image 2.if there are white(255) pixels are more than other pixels then I have to keep 255 and replace center pixel value by 255 3.if there are below (255) pixels are more inside that 3x3 window... Then I have to take average of below(255)pixels then have to take average of only below(255) pixels and replace as the center pixel value I have to take 255(white pixels) as center during sliding a 3x3 window I need a code for it please do help with loop I need because I have to take all 255(white)pixels in a image and have to change the value of each and every white pixel

Sir I have found out the pixel values using coordinates (x, y) = find(I==255) I got the each and every coorodintes and pixels of 255(white) from this now I need to apply averaging as I explained above for every pixel Please do help me with the code

justin gat 2021-5-30

ok sir now i will tag u and will write a question

thank you i need it as soon as possible

justin gat 2021-5-30

https://in.mathworks.com/matlabcentral/answers/843645-how-to-average-specific-pixels-on-a-3x3-window-and-count-the-number-of-pixels-present-in-it

sir here the question please do help sir

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Image Analyst 2012-11-14

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编辑：Image Analyst 2012-11-14

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Don't worry about the warning. Your code can be done like this:

blurredImage = conv2(single(yourGrayScaleImage), ones(3)/9, 'same');
imshow(blurredImage, []); % or imshow(uint8(blurredImage), [0 255]);

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Franzi 2020-6-7

Hello? Are you still there? Do you know the function reshape and how to use it?

Image Analyst 2020-6-7

You'd have to reshape the image into a column of 3 pixels. Then use repelem() to repeat each column because the windows overlap don't they? You don't want them to jump, right. Then use a for loop to go down the columns. You'd have to think about it. It gets tricky because you'll have to have each pixel in there 9 times so it's tricky to figure out how to do that with repelem() and reshape(). It's much more difficult when they don't let you do it the simple and obvious ways. It's MUCH easier if they let you move the window in jumps of 3 pixels over and down rather than 1 pixel over and down.

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sateesh kumar 2020-4-16

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Dont worry about Warning/Display Warning of too big size, you can simply write warning off at the starting of program.

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Nitishselvakumar Nadar 2021-4-22

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img = imread("Tulip.jpg");
[row ,col] = size(img);
for i = 2:1:row-1
    for j = 2:1:col-1
        x= img(i+1:i-1,j+1:j-1);
        C=x(:)';
        C=sort(C);
        avg = sum(C)/9;
        img(i,j) = avg;
        
    end
end
imshow(img);

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mohammad sheikholmolok 2022-11-27

移动：DGM 2022-11-27

I write for you the correct code

DGM 2022-11-27

编辑：DGM 2022-11-27

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If you're going to offer an improved bit of code, explain why it's better.

This is still a lot of room for improvement.

% read an image
inpict = imread('cameraman.tif'); % use unambiguous variable names
% what stops this from breaking if the image is RGB?
[row,col,~] = size(inpict); % always discard the last output from size()
outpict = zeros(row,col,class(inpict)); % preallocate to appropriate class
for i = 2:1:row-1 % avoiding the edges is a simple strategy, but not very good
    for j = 2:1:col-1 % a better way would be edge padding/replication
        % get a sample
        sampleblock = inpict(i-1:i+1,j-1:j+1);
        % don't need a bunch of temporary variables or unused lines
        % RHS is uint8-scale double
        % LHS is uint8
        % the assignment implicitly uses round() when casting
        outpict(i,j) = mean(sampleblock(:));
    end
end
% don't need a bunch of redundant images
montage({inpict outpict})