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

[Antoine Monmayrant]

Hi Jasper,

Thanks for your proposition.
I came to a similar conclusion (see my reply to Mike).
I was wondering whether there was something more efficient to implement.
I am sure this kind of problem as already been solved in many areas but 
I don't have the right keywords to search for.
If I don't find anything better, I'll implement something along the 
lines of what you've proposed.
I am just afraid that this approach will be too slow given the size of 
my matrices.

Thank you for your help,

Antoine

Le 08/03/2011 11:27, jasper van baten a écrit :
> 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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>


-- 
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  Antoine Monmayrant LAAS - CNRS
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  Tel:+33 5 61 33 64 59

  email : antoine.monmayrant at laas.fr
  permanent email : antoine.monmayrant at polytechnique.org

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