Problems with coursera image blur matlab problem

Question

ey21 2020-4-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/517643-problems-with-coursera-image-blur-matlab-problem

回答： Muhammad Qaisar Ali 2020-6-27

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Hey all,

I am near completing the introduction to matlab programming course on Coursera.

function[output] = blur(img,w) 
change = w; 
emptymatrix = zeros(length(img(:,1)),length(img(1,:))); 
for z = 1:length(img(1,:))
    for i = 1:length(img(:,1)) 
        if (i + change) <= length(img(:,1)) && (i - change) >= 1 && (z + change) <= length(img(1,:)) && (z - change) >= 1
         submatrix = img((i-change):(i+change),(z-change):(z+change)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix); 
        elseif i == 1 && z == 1
         submatrix = img((i):(i+change),(z):(z+change)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix); 
        elseif i == length(img(:,1)) && z == length(img(1,:)) 
         submatrix = img((i-change):(i),(z-change):(z)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix); 
        elseif i == 1 && z == length(img(1,:)) 
         submatrix = img((i):(i+change),(z-change):(z)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix);  
        elseif i == length(img(:,1)) && z == 1
         submatrix = img((i-change):(i),(z):(z+change)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix); 
        elseif i == 1 && z-change >= 1 && z+change <= length(img(1,:)) 
         submatrix = img((i):(i+change),(z-change):(z+change)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix); 
        elseif i == length(img(:,1)) && z-change >= 1 && z+change <= length(img(1,:)) 
         submatrix = img((i-change):(i),(z-change):(z+change)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix);   
        elseif z == 1 && i-change >= 1 && i+change <= length(img(:,1))
         submatrix = img((i-change):(i+change),(z):(z+change)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix);    
        elseif z == length(img(1,:)) && i-change >= 1 && i+change <= length(img(:,1))
         submatrix = img((i-change):(i+change),(z-change):(z)); 
         emptymatrix(i,z) = uint8(sum(submatrix(:))/numel(submatrix));
         output = uint8(emptymatrix); 
        end
    end
end
output = uint8(output); 
end

I have attached a screenshot of the problem below and of the output the online program is giving me.

Could anyone give me a helping hand as to where I am going wrong?

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Answer 1

Walter Roberson 2020-4-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/517643-problems-with-coursera-image-blur-matlab-problem#answer_425869

编辑：Walter Roberson 2020-4-13

在 MATLAB Online 中打开

I would suggest to you that you could save a lot of code by using max() and min() on the coordinates, like

max(1, column-w):min(column+w, number_of_columns)

That will get you a block of values that you can take the mean of.

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Emre Yavuz 2020-4-14

编辑：Walter Roberson 2020-4-14

在 MATLAB Online 中打开

@ Walter Roberson, I have edited my code below but it is still not accepting...

function[output] = blur(img,w) 
change = w; 
emptymatrix = uint8(zeros(size(img)));  
for z = 1:length(img(1,:))
    for i = 1:length(img(:,1)) 
        if (i + change) <= length(img(:,1)) && (i - change) >= 1 && (z + change) <= length(img(1,:)) && (z - change) >= 1
         submatrix1 = img((i-change):(i+change),(z-change):(z+change)); 
         emptymatrix(i,z) = (sum(submatrix1(:))/numel(submatrix1)); 
        elseif i == 1 && z == 1
         submatrix2 = img((i):(i+change),(z):(z+change)); 
         emptymatrix(i,z) = (sum(submatrix2(:))/numel(submatrix2));
        elseif i == length(img(:,1)) && z == length(img(1,:)) 
         submatrix3 = img((i-change):(i),(z-change):(z)); 
         emptymatrix(i,z) = (sum(submatrix3(:))/numel(submatrix3));
        elseif i == 1 && z == length(img(1,:)) 
         submatrix4 = img((i):(i+change),(z-change):(z)); 
         emptymatrix(i,z) = (sum(submatrix4(:))/numel(submatrix4));  
        elseif i == length(img(:,1)) && z == 1
         submatrix5 = img((i-change):(i),(z):(z+change)); 
         emptymatrix(i,z) = (sum(submatrix5(:))/numel(submatrix5));
        elseif i == 1 && z-change >= 1 && z+change <= length(img(1,:)) 
         submatrix6 = img((i):(i+change),(z-change):(z+change)); 
         emptymatrix(i,z) = (sum(submatrix6(:))/numel(submatrix6));
        elseif i == length(img(:,1)) && z-change >= 1 && z+change <= length(img(1,:)) 
         submatrix7 = img((i-change):(i),(z-change):(z+change)); 
         emptymatrix(i,z) = (sum(submatrix7(:))/numel(submatrix7)); 
        elseif z == 1 && i-change >= 1 && i+change <= length(img(:,1))
         submatrix8 = img((i-change):(i+change),(z):(z+change)); 
         emptymatrix(i,z) = (sum(submatrix8(:))/numel(submatrix8)); 
        elseif z == length(img(1,:)) && i-change >= 1 && i+change <= length(img(:,1))
         submatrix9 = img((i-change):(i+change),(z-change):(z)); 
         emptymatrix(i,z) = (sum(submatrix9(:))/numel(submatrix9));
        end
    end
end
output = emptymatrix; 
end 

I believe I have covered every index in the empty matrix but somehow when I print the emptymatrix at the end, there are some zeros appearing where there should be non-zero numbers.

For example when my input matrix is this:

 225   225   225   225
   0     0     0   225
   0     0     0   225
   0     0     0   225
 225   225   225   225

[output] = blur(img,2)

Gives me:

  5×5 uint8 matrix
   0   135     0   125
   0     0     0     0
   0   144     0   135
   0     0     0     0
   0   135     0   125

But I believe it should give me:

  5×5 uint8 matrix
 113   135   113   125
  98   124    98   113
 124   144   124   135
  98   124    98   113
 113   135   113   125

Walter Roberson 2020-4-14

I can't think of a reason to have it there.

Emre Yavuz 2020-4-14

@ Walter Roberson, agreed!

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Answer 2

Muhammad Qaisar Ali 2020-6-27

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/517643-problems-with-coursera-image-blur-matlab-problem#answer_457816

在 MATLAB Online 中打开

function output = blur(img,w);
    
    [r,c]=size(img);
    output=ones(r,c);
    for ri=1:r
        for ci=1:c
            % checking for indicies,and making limits for sub matrix.
            if ri-w<1
                sub_mat_all_row_indicies=1:(ri+w);
            elseif ri+w>r 
                sub_mat_all_row_indicies=(ri-w):r;
            else
                sub_mat_all_row_indicies=(ri-w):(ri+w);
            end
            
            if ci-w<1
                sub_mat_all_col_indicies=1:(ci+w);
            elseif ci+w>c 
                sub_mat_all_col_indicies=(ci-w):c;
            else            
                sub_mat_all_col_indicies=(ci-w):(ci+w);
            end
            sub_mat=img(sub_mat_all_row_indicies,sub_mat_all_col_indicies);        %make sub matrix/window.
            % bluring or averaging.
            output(ri,ci)=mean(sub_mat(:));
        end
    end
    output=uint8(output);       %converting to grayscle. 0 to 255.
end