It is bad to ask such questions......asking to explain a specific line or a code. You have code in hand, play around with that. Print the values, run the code in debug and you can make yourself clear with the code.
bla = k(:,:,1) > 0;
In the above case bla is a logical matrix. It will have 0, and 1's. 0 where the condition >0 is not met and 1's where the condition > 0 is met.
if(bla(y,x))
In the above line a if condition is used, the conditon is met or if is executed if bla(x,y) is 1 or the if contion is not met.
