Code Understanding Help Needed

2 views (last 30 days)
Hello, I have some problems in understanding this piece of code. Anybody's help will be really appreciated.
lambda=100;
level=1;
im=im2double(curr_frame);
scrib=im2double(curr_trimap);
scrib=reshape(scrib(:,:,1),[],1);
nn=[10;2];
[m n d]=size(im);
val=scrib>0.99;
map=(scrib<0.01)+val;
[a b]=ind2sub([m n],1:m*n);
feature=[reshape(im,m*n,d)';[a;b]/sqrt(m*m+n*n)*level+rand(2,m*n)*1e-6];
now=0;
for i=1:size(nn,1)
ind=vl_kdtreequery(vl_kdtreebuild(feature),feature,feature,'NUMNEIGHBORS',nn(i),'MAXNUMCOMPARISONS',nn(i)*2);
a=reshape(repmat(uint32(1:m*n),nn(i),1),[],1);
b=reshape(ind,[],1);
row(now+1:now+m*n*nn(i),:)=[min(a,b) max(a,b)];
feature(d+1:d+2,:)=feature(d+1:d+2,:)/100;
now=now+m*n*nn(i);
end
value=max(1-sum(abs(feature(1:d+2,row(:,1))-feature(1:d+2,row(:,2))))/(d+2),0);
A=sparse(double(row(:,1)),double(row(:,2)),value,m*n,m*n);
A=A+A';
D=spdiags(sum(A,2),0,n*m,n*m);
M=D-A+lambda*spdiags(map,0,m*n,m*n);
L=ichol(M);
x=pcg(M,lambda*val,[],2000,L,L');
% figure,imshow(reshape(x,m,n));
% imwrite(reshape(x,m,n),'res.png','png');
Alpha = reshape(x,m,n);
val=scribe>0.99; it will assign 1 to the values greater than 0.99 and all others =0. Now next is map=(scrib<0.01)+val; How the values will be assign here? Please explain this condition. Also, please explain this line:
feature=[reshape(im,m*n,d)';[a;b]/sqrt(m*m+n*n)*level+rand(2,m*n)*1e-6];
I am unable to understand this line.
Please help. Thanks

Accepted Answer

Image Analyst
Image Analyst on 2 Aug 2015
The first line (where you renamed scrib to scribe)
val=scribe>0.99
creates a binary/logical variable called val that is true/1 for any element in scrib (or scribe) that is greater than 0.99, and false/0 for any element that is 0.99 or less.
The second line
map=(scrib<0.01)+val;
first creates a temporary binary/logical array where it's true for any element where scrib is less than 0.99. Then, because it's using + instead of &, it casts val to double, then casts the temporary logical variable to double, then adds them together to form a new double variable called map. Most good MATLAB programmers would have done it this way instead:
map = (scrib<0.01) & val;
so map would have been a logical variable also.
The third line :
feature=[reshape(im,m*n,d)';[a;b]/sqrt(m*m+n*n)*level+rand(2,m*n)*1e-6];
creates an array by concatenating vertically two other arrays. The first part, reshape(im,m*n,d), takes all the pixels in the image and puts them into a column vector. If the image is color, you will have the green and blue channels in columns 2 and 3 respectively. Then it transposes it so they are in row vectors. Then it concatenates a scaled version of the badly named a and b underneath that.
The reason it's hard to follow is that this is poorly written code. It's an alphabet soup mess of a code with no comments, variable names that are single letters with no clue as to what they mean, describe, or represent, and use variable names (like "now") that destroy built-in functions. Don't be like this programmer. Instead, read this link and be better than them.

More Answers (0)

Tags

No tags entered yet.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!