from 0 1 matrix to boundaries and vertices

I have a matrix like the one is attached here I want to overwrite on the ones:

• 2 if the cell is a edge
• 3 if the cell is a vertex

like from:

1 1 1 1 1

1 1 1 1 1

0 1 1 1 0

to:

3 2 2 2 3

3 3 1 3 3

0 3 2 3 0

any idea?

[Dyuman Joshi]

What is the criteria for an element being an edge and an element being a vertex?

[Andrea Somma]

like a polygon if the line breaks then is a vertex, otherwise if the line of 1 is near a line of zeros then is a edge like this:

from:

1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1

0 0 1 1 0 0 0 0

0 0 1 1 0 0 0 0

to:

3 2 2 2 2 2 2 3

2 2 2 2 2 2 2 2

2 2 2 2 2 2 2 2

3 2 3 3 2 2 2 3

0 0 2 2 0 0 0 0

0 0 3 3 0 0 0 0

[Andrea Somma]

this is a bit involved but works let me know if someone can come up with a faster solution

load("matlab.mat")

nx = size(domain,2);
ny = size(domain,1);

% storing old domain
odomain = domain;

%% matrix boundaries
ev = zeros(size(domain));

for i = 2:nx-1
    j = 1;
    if domain(j,i) == 1
        ev(j,i) = 1;
    end
    if domain(j,i) == 1 && (domain(j,i-1)==0 || domain(j,i+1)==0)
        ev(j,i) = 2;
    end

end

for i = 2:nx-1
    j = ny;
    if domain(j,i) == 1
        ev(j,i) = 1;
    end
    if domain(j,i) == 1 && (domain(j,i-1)==0 || domain(j,i+1)==0)
        ev(j,i) = 2;
    end

end

for i = 2:ny-1
    j = 1;
    if domain(i,j) == 1
        ev(i,j) = 1;
    end
    if domain(i,j) == 1 && (domain(i-1,j)==0 || domain(i+1,j)==0)
        ev(i,j) = 2;
    end

end

for i = 2:ny-1
    j = nx;
    if domain(i,j) == 1
        ev(i,j) = 1;
    end
    if domain(i,j) == 1 && (domain(i-1,j)==0 || domain(i+1,j)==0)
        ev(i,j) = 2;
    end
end

if domain(1,1)==1 
    ev(1,1) = 2;
end

if domain(1,nx)==1 
    ev(1,nx) = 2;
end

if domain(ny,1)==1 
    ev(ny,1) = 2;
end

if domain(ny,nx)==1 
    ev(ny,nx) = 2;
end

%% internal points
for i = 2:nx-1
    for j = 2:ny-1
        if sum([domain(j-1,i) domain(j+1,i) domain(j,i-1) domain(j,i+1) ...
                domain(j-1,i+1) domain(j+1,i-1) domain(j-1,i-1) domain(j+1,i+1)]) == 5
            ev(j,i) = 1;
        elseif sum([domain(j-1,i) domain(j+1,i) domain(j,i-1) domain(j,i+1) ...
                domain(j-1,i+1) domain(j+1,i-1) domain(j-1,i-1) domain(j+1,i+1)]) == 6
            ev(j,i) = 1;
        elseif sum([domain(j-1,i) domain(j+1,i) domain(j,i-1) domain(j,i+1) ...
                domain(j-1,i+1) domain(j+1,i-1) domain(j-1,i-1) domain(j+1,i+1)]) == 7
            ev(j,i) = 2;
        end
    end
end

%% resulting domain
domain = domain + ev;
domain(odomain<1) = 0;

imagesc(odomain)

figure
imagesc(domain)

Answer 1

[Matt J]

A=load('domain').domain; A=imresize(A,1/20);


BW=logical(A);

A(BW)=2;

BW=bwmorph(BW,'remove');

A(A&~BW)=1;

BW=edgeLengthen(BW,5,0)+edgeLengthen(BW,5,1)>0;

v=bwmorph(BW,'branchpoints');

A(v(2:end-1,2:end-1))=3; %final result

imshow(A,[])

function BW=edgeLengthen(BW,n,rowwise)

 BW=padarray(BW,[1,1]);
 se0=ones(1,n-2);
 se1=ones(1,n+2);
 if ~rowwise, se0=se0'; se1=se1'; end

 BW=imerode(BW,se0);
 BW=imdilate(BW,se1);

end

[Andrea Somma]

Thank you! I will download image processing toolbox and will try it