How to find non zeros in multiple matrices ?

Hi,

I have an issue with my program :

Basically I have a stack of 20 images (555*555 pixels each) and I want to record the coordinates of a bright object on each image. For that, I use the function imbinarize that returns a 555*555 matrix of 0 (backgroud) and 1 (bright object). I have now a Bin=555*555*20 matrix with all the 0 and 1 of my 20 images.

My problem is that when I use the find fuction : [a,b]=find(Bin(:,:,1:20)==1); it works for the variable a that gives me all the y (horizontal) coordinates that have 1 for value but the value b only works for the first image (for the other images b is superior to 555 which is normally the maximal coordinate !).

Can you please help me with that ?

Thanks a lot

Answer 1

[Jakub]

Variable b holds linear indices corresponding to second and third dimension. That's why it exceeds the size of array. A possible solution is to use linear indexing from start followed by ind2sub:

k = find(Bin(:,:,1:20)==1);
[a,b,nimage] = ind2sub(size(Bin),k);

Answer 2

[fish minox]

Yes it works ! Thank you very much for the fast answer man!I need to dig in this linear indexing thing, looks powerful. thanks again!