[scilab-Users] Finding continuous parts in a mask (ie a binary matrix)

[jasper van baten]

Hello Antoine,

Use a flood fill. Make a matrix with the same size as your original 
to keep track of which elements you already checked.

Loop until there are no more elements you did not check with a value of 1:

  - make a list of elements to check, add the first unchecked element 
with value of 1
  - make a list of elements in the grain, initially empty.
  - while there are elements in the to-check list:
     - add this element to the grain list
     - mark this element as checked in the matrix
     - add all of its unchecked neighbours to the to-check list
  - the grain list now contains all elements in a grain. All elements 
in this grain are marked checked. Scan for the next grain.

Hope that helps.

Jasper.


At 11:21 3/8/2011, Mike Page wrote:
>Hi Antoine,
>
>You could use a Sobel transform to detect the edges where the value changes
>from 0 to 1 or 1 to 0.
>
>But maybe you were looking for something simpler?
>
>Mike.
>
>
>-----Original Message-----
>From: Antoine Monmayrant [mailto:antoine.monmayrant at laas.fr]
>Sent: 08 March 2011 09:58
>To: users at lists.scilab.org
>Subject: [scilab-Users] Finding continuous parts in a mask (ie a binary
>matrix)
>
>
>Hi everyone,
>
>I have question that is more about image filtering than scilab, but I
>haven't found any answer so far so I'm turning towards scilab users.
>I am looking for a way to determine continuous parts in a matrix made of
>1 or 0.
>Basically, this matrix is used as a mask to filter an image and I need
>to determine the number of isolated "grains" (ie continuous parts where
>the matrix is equal to 1) in this mask.
>As an example, here is a mask:
>
>-->mask
>   mask  =
>
>      0.    0.    0.    0.    0.    0.    0.    0.    0.    0.
>      0.    0.    0.    0.    0.    0.    1.    1.    1.    0.
>      0.    0.    0.    0.    0.    0.    1.    1.    1.    0.
>      0.    0.    0.    0.    0.    0.    1.    1.    1.    0.
>      0.    1.    1.    0.    0.    0.    0.    0.    0.    0.
>      0.    1.    1.    1.    0.    0.    0.    0.    0.    0.
>      0.    0.    1.    1.    0.    0.    0.    0.    0.    0.
>      0.    0.    0.    0.    0.    0.    0.    0.    0.    0.
>      0.    0.    0.    0.    0.    0.    0.    0.    0.    0.
>      0.    0.    0.    0.    0.    0.    0.    0.    0.    0.
>
>
>It contains 2 "grains", one in the upper-right corner, and one in the
>middle-left.
>I would like to be able to isolate them in order to determine their
>position in the matrix, size,...
>Do any of you know of a good algorithm to achieve this?
>Do any of you know what are the relevant names or keywords associated to
>this kind of algorithm?
>
>Thank you in advance,
>
>Antoin
>
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