how to clear the border of matrix?

I have a label image matrix

img=
    1 1 1 2 2 2 3 3 3 3
    1 2 2 2 9 3 3 3 3 3
    1 1 9 9 9 9 9 9 3 3
    1 8 8 8 8 8 8 8 8 3
    1 8 8 8 7 7 7 7 7 3
    1 7 7 7 7 1 1 7 7 3
    1 1 1 1 1 1 1 1 1 1

I want to clear the side border and register it and clear the inside matrix with the value is same as side so turn them into 0.

side=
        1 1 1 2 2 2 3 3 3 3
        1                 3
        1                 3
        1                 3
        1                 3
        1                 3
        1 1 1 1 1 1 1 1 1 1

side =(1,2,3)

result=
      0 0 0 0 0 0 0 0 0 0
      0 0 0 0 9 0 0 0 0 0
      0 0 9 9 9 9 9 9 0 0
      0 8 8 8 8 8 8 8 8 0
      0 8 8 8 7 7 7 7 7 0
      0 7 7 7 7 0 0 7 7 0
      0 0 0 0 0 0 0 0 0 0

Answer 1

[Guillaume]

It's actually very simple using set operations:

 img = [1 1 1 2 2 2 3 3 3 3
        1 2 2 2 9 3 3 3 3 3
        1 1 9 9 9 9 9 9 3 3
        1 8 8 8 8 8 8 8 8 3
        1 8 8 8 7 7 7 7 7 3
        1 7 7 7 7 1 1 7 7 3
        1 1 1 1 1 1 1 1 1 1];

result = img;
result(ismember(result, union(result(:, [1 end]), result([1 end], :)))) = 0

union gives you the unique labels that are part of the vertical and horizontal borders. ismember tells you which labels at what position are parts of that union. You then use the logical vector generated by ismember to set the respective labels to 0.

Answer 2

[Image Analyst]

If you want, you can just set the rows and columns to zero

   img = [1 1 1 2 2 2 3 3 3 3
          1 2 2 2 9 3 3 3 3 3
          1 1 9 9 9 9 9 9 3 3
          1 8 8 8 8 8 8 8 8 3
          1 8 8 8 7 7 7 7 7 3
          1 7 7 7 7 1 1 7 7 3
          1 1 1 1 1 1 1 1 1 1];

result = img;
result(1,:)=0;
result(end,:)=0;
result(:,1)=0;
result(:,end)=0

[Image Analyst]

By the way, this doesn't look like a labeled image because you don't have paths of zeros separating the blobs. And if it's a labeled image that came from a binary image and you didn't want to include blobs that touched the border (because the object is only partially there), you'd use imclearborder().

Rather, it looks exactly like a classified image where each pixel is assigned a class, like background, material 1, material 2, etc.

[Tan Wen Kun]

This because I ask on matrix so I didnt write out the border

Because my object is always on the center so I want register the border and then made the value inside which same as border into 0

[Image Analyst]

I don't understand any of what you said. But whatever . . . you've accepted Guillaume's answer so I guess your problem is resolved now and that's what counts. Good luck.

[Tan Wen Kun]

Because I doing some dumb image segmentation so sometime my question is look abit foolish~my lecturer just give me the step that whatever now me can do in time so my work is abnormal than normal image segmentation