What is this filtering algorithm called?

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John Snow 2014-1-7

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https://ww2.mathworks.cn/matlabcentral/answers/111666-what-is-this-filtering-algorithm-called

关闭： MATLAB Answer Bot 2021-8-20

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Hello, can somebody explain to me how the following code works or tell me the name of the method used to filter the left binary image to the right one?

Image:

Code:

[rows, cols] = size(e);
L1 = 20;
L2 = 80;
seed = [];
for alpha = 40:120
    dx = cos( alpha * pi / 180);
    dy = sin( alpha * pi / 180);
      for d = L1:L2
          r =  round(cy - d * dy );
          c =  round(cx + d * dx );
          found = 0;
          for i = -2:2
              for j=-2:2
                  ri = r + i;
                  cj = c + j;
                  if( ri < 1 || ri > rows || cj < 1 || cj > cols || found )
                      continue;
                  end;
                  if( e(ri, cj) )
                      found = 1;
                      seed = [ seed, sub2ind( [rows, cols], ri, cj ) ];
                  end;
              end;
          end;
          if( found>0 )
              break;
          end;
      end;
  end;
newe = ones( rows, cols ) > 2;
for k=1:length(seed)
    [r,c] = ind2sub( [rows, cols], seed(k) );
      if( e(r,c)  )
          e(r,c) = 0;
          q = seed(k);
          newe(r,c) = 1;
          while( ~isempty(q) )
              id = q(1); q = q(2:end);
              [r,c] = ind2sub( [rows, cols],id);
              for i=-1:1
                  for j=-1:1
                      ri = r+i;
                      cj = c+j;
                      if( ri < 1 || ri > rows || cj < 1 || cj > cols )
                          continue;
                      end;
                      if( e(ri, cj)  )
                          e(ri, cj) = 0;
                          newe( ri, cj ) = 1;
                          q = [q, sub2ind( [rows, cols], ri, cj ) ];
                      end;
                  end;
              end;
          end;
      end;
  end;
newe = bwmorph( newe, 'dilate', 2 ); 
newe = bwmorph( newe, 'thin', inf );