Help me get this shape on the masks

I have some masks and i want to create a shape like a freeform donut that will enclose the masks,

I have drawn by red and green of what i want.

Answer 1

[Matt J]

This requires a File Exchange download,

https://www.mathworks.com/matlabcentral/fileexchange/71226-tspsearch

load BW

dsk=@(r)strel('disk',r);

A=BW;

outer=~bwconvhull(A);

B=A|outer;

C=imopen(~B,dsk(2));

D=bwareafilt(C,1);

E=imfill(D|A,'holes'); %Closed shape

G=getInner(E,A); %Green (inner) boundary

R=bwmorph(imdilate(E,dsk(3)),'remove'); %Red (outer) boundary

rgb=255*cat(3,R,G,0*G) + (A&~(R|G));
imshow(rgb,[]); hold on
hold off

shg


function G=getInner(R,A)
 
  [m,n]=size(A);

  K=imdilate(A,ones(3))&imfill(R,'holes')&~A;

  [I,J]=find(K); 
  [I,J]=orderPath(I,J);

   V=[I,J];
   for j=1:2

       delta=vecnorm(diff(V,1,1),2,2);
       v=find(delta>10);  
       v(end+1)=height(V); 

       discard=false(height(V),1);
       for k=1:numel(v)
           discard=trimfunc(V,v(k),discard);   
       end

    
       V(discard,:)=[];  
       V=flipud(V);
   end

    G=poly2mask(V(:,2),V(:,1),m,n);
    G=bwmorph(  bwmorph(G,'thin',1) ,'remove');

end

function discard=trimfunc(V, i, discard)

 T=V(i-40:i,:); %HARDCODE=40

 t0=T(1,:);
 d=T(end,:)-t0;

 T=T-t0;

 c=T/d;

 dists=vecnorm(T-c.*d,2,2);

 imax=find(dists==max(dists),1,'last');
 
 discard(i-40+imax-3:i,:)=1;

end


function [I,J]=orderPath(I,J)
  is=tspsearch([I,J],5);
  I=I(is); 
  J=J(is);
  k=find( hypot(diff(I), diff(J))>5 , 1);
  I=circshift(I,-k);
  J=circshift(J,-k);
end

[kunal]

Wow, This ia amazing. Works way too good.

can i trouble you with one more think how can i get something similar to this but in the inner side of the mask The green line i drew in the image i share

[Matt J]

I've added it, but it requires a File Exchange download.

[kunal]

ok. I will look in it. Thanks a lot for your help

Answer 2

[Image Analyst]

Try bwboundaries and alphaShape

https://www.mathworks.com/help/releases/R2024b/matlab/ref/alphashape.html