SIP Toolbox

follow - A contour follower

Calling Sequence

[x,y] = follow(Img)
[x,y] = follow(Img, 4)
[x,y] = follow(Img, 8)

Parameters

Description

Function follow extracts parametric contours of binary objects. This is useful for further extracting object features such as curvature and bending energy.

It is assumed that Img has only one object.

x and y both store the parametrized contour. That is, (x(i),y(i)) is a point of the contour, where the coordinate system is assumed as starting from bottom-left corner (0,0) to uper-right corner of the image. To get the (row,col) matrix coordinates, use the transformation below:

      row = size(Img,'r') - y
      col = x+1
 

The second argument is an optional parameter, being 4 or 8 depending if the border following is to be made in 4- or 8-neighborhood sequence, yielding a 4- or 8-connected contour.

follow(Img) equals follow(Img, 8).

Examples

       initial_dir = PWD;
       chdir (SIPDIR + 'images');

       Img = imread('star.bmp');
       xset('window',0)
       xbasc()
       imshow(Img,2);
       [x,y] = follow(Img);
       xset('window',1)
       xbasc()
       plot2d(1:size(x,'*'),x,2);
       plot2d(1:size(y,'*'),y,1);

       chdir(initial_dir);
   

Authors

Ricardo Fabbri <ricardofabbri (AT) users DOT sf DOT net>

Bibliography

"Shape Analysis and Classification", L. da F. Costa and R. M Cesar Jr., CRC Press, pp. 335-347.

Availability

The latest version of the Scilab Image Processing toolbox can be found at

http://siptoolbox.sourceforge.net

See Also

unfollow,  gsm,  bwborder,  curvature,