Replacing centre pixel value

        I have a code ,of 7x7 natrix in that for each 3x3 i have found minimum value and if that minimum value is greater the centre pixel value ,the centre pixel value must be replaced by 5.have problem in replacing centre pixel value ,please help

for i=2:6
    for j=2:6
        K= A(i-1:i+1,j-1:j+1);
        T=K(2,2);finding centre pixel value

          B=min(K(:));
          if B>T

              %%%please tell what must come here replacing centre pixel vaue by 5

              %%%%I DID   K(2,2)=5;

          else
              %%%%%%%%%here also
              %%I DID K=K;
          end
      end
  end

BUT I GET 3x3 matrix only,how to get 7x7 matrix
please assist

        please assist

[Image Analyst]

You've been posting here long enough that you should already know how to format your questions. Please review the tutorial http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup. By the way, you can type Ctrl-A, Ctrl-I, Ctrl-C when your code is in MATLAB to fix indenting problems. Then come here and paste it in, highlight it, and click {}Code. Do not have any spaces before non-code text (like your first paragraph). It's not hard - give it a try.

Answer 1

[Image Analyst]

The minimum value in a 7x7 window will never be greater than the center value. Please explain what you are thinking.

By the way, you can call imerode() to get the local min values in a 7x7 sliding window.

[FIR]

Just it is an example ,i want to try on my own ,the concept which i was given,the above explaination is just the concept,finallyy i need 7x7 but i get only 3x3

[Image Analyst]

But the concept is flawed! Anyway, you might play around and use imerode and subtract it from your original, or vice-versa. Then threshold and replace items meeting the threshold with 5. I think you already know how to do that without loops. Even if you did want to use loops, you'd have to have 4 loops, not 2. Two to scan rows and columns, and then at each pixel, another two loops (like you already have) to scan a window around that pixel. But not a very efficient way to do it. I suggest you review the code examples I gave you in your prior, related questions.

[FIR]

Can u please post an example here please,i could nor review the codes since there are many questions posted by me

Answer 2

[Walter Roberson]

A(i,j) = 5;

[FIR]

s walter but i get only 3x3 window,but i need 7x7

[Walter Roberson]

Your question in your code comments was

%%please tell what must come here replacing centre pixel vaue by 5

and that assignment answers that question.

If you want a 7 x 7 window then replace

K= A(i-1:i+1,j-1:j+1);

with

K= A(i-3:i+3,j-3:j+3);

[FIR]

I GET ERRPR

 Subscript indices must either be real positive integers or logicals.

7X7 window i meant is after processing ,in the code above i have taken 3x3 and have processed ,in which my last 3x3 window is displayed.but how to display as 7x7 which is after processing,and same size of input matrix

[Walter Roberson]

In that case do not use K= A(i-3:i+3,j-3:j+3); and use the original instead, and use

A(i,j) = 5;

like I originally indicated. The output will be A.

This is for replacing the center pixel like you asked. It probably isn't what you wanted, though, as replacing the center pixel as you proceed is going to affect the computations to the right and below. What you probably want is to output a new array that is like the original array but with the center pixels replaced. Such as

newA = A;

for i=2:6
  for j=2:6
    K= A(i-1:i+1,j-1:j+1);
    T=K(2,2);finding centre pixel value
    B=min(K(:));
    if B>T
      newA(i,j) = 5;
    else
      %I could not tell what you want done in this case
    end
  end
end

[FIR]

ok walter thanks

can u guide me in quanterion switching filter,please

[Walter Roberson]

I do not know anything about quaternion switching filters.