Index in position 1 is invalid. Array indices must be positive integers or logical values?

I have tried to create a filter the two function below: averageFilter and maskaverage but im getting this error

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in maskaverage (line 12)
           summation = summation + img(sr,z);

Error in af (line 9)
              image(i,j) = maskaverage(image,i,j,k);

function img = averageFilter(image, M, N,k)
%sr : starting row, er : ending row, sc : starting column, ec : ending column
    sr=ceil(k/2);
    er =(M-floor(k/2));
    sc=ceil(k/2);
    ec=(N-floor(k/2));
    for i=sr:1:er
        for j= sc:1:ec
              image(i,j) = maskaverage(image,i,j,k);
        end
    end
    img=image;
end

function summation = maskaverage(img,i,j,k)

  sr = i - floor(k/2);
  er = i + floor(k/2);
  sc = j - floor(k/2);
  ec = j + floor(k/2);
  summation = 0;
 
  %traversing spirally
  while(sr<er && sc < ec)
      %traverse through first row
       for z = sc:ec
           summation = summation + img(sr,z);
       end
       sc=sc+1;
      %traverse through last row
       for z=sr:er 
           summation = summation + img(z,ec);
       end
       ec=ec-1;
      %traverse through last row from the remaining row
       if(sr<er)
           for z=ec:sc   
               summation = summation + img(er,z);   
           end
            sr=sr-1;
       end
       %print first col from the remaining
       if(sc<ec)
           for z= er:sr 
               summation=summation + img(z,sc) ;
           end
           sc=sc+1;
       end
   end
  summation = summation/(k*k);

end

Answer 1

[Cris LaPierre]

What is the size of img? What is the value of sr in line 12?

summation = summation + img(sr,z);

The error would suggest a problem with the value of sr. In particular, it sounds like sr is either less than 1 or not an integer. We don't have enough information into the various variable values used to ultimately calculate sr to tell you for certain.

[JAPHUNGSHAR BRAHMA]

Yes, there was an error with the code in maskaverage function i.e i incremented 'sc' instead of 'sr' and decremented sr instead of er . Also decremenation step by -1 in z=ec:sc and z= er:sr.

Its works fine now as an average filter. Btw Thanks for your effort.