What does the operator "~=" mean?

max2 = @(x) max(max(x));
immax = nlfilter(im, [siz siz], max2);
im(im ~= immax) = 0;
result = im;

This is the code take from a non-maximum suppression function. What does the 3rd line mean? Why can we use "something(something) = 0;" as a statement?

Thank you.

[Image Analyst]

Why not just us imregionalmax()?

Answer 1

[Shashank Prasanna]

something(somthing_else)=0; In MATLAB refers to logical indexing and assignment.

In this case somthing_else has to be logical (think boolean) and

im ~= immax

basically means values where those to are not equal will be true and the rest will be false. When that is followed by:

im(im ~= immax) = 0;

you are equating to zero all the values in im where the above condition is not satisfied.

you will find this information in the documentation under logical indexing.

[Linux]

Thank you very much.

[Paul Metcalf]

Don't feel bad, ~= is one of the first real gotcha's in MATLAB and threw me for a while when I started out. For a long time, I read it as "approximately equal to" rather than "not equal to", quite a fundamental difference. I'm sure there's a big story somewhere about why it's not the standard !=...