Error in 'find' function when value is out of range. How to get around?

I have eight thicknesses, Th=0,5,10,15,20,25,30,35,40. For each of the Th, I have matrix, ratioAB.

Then, I have Z that is a 2D matrix consisting of pixels with different thicknesses. For each of the pixel, I need to find the correct ratioAB depending on the thickness. The result, RF, should be a matrix of ratioAB.

Because the Th range from 0 to 40, when I have negative value or value more than 40 in the Z matrix, I get the error 'Subscript indices must either be real positive integers or logicals.'

How do I fix the code?

m=1024;
n=1024;
Th = [0,5,10,15,20,25,30,35,40];
i=1:length(Th)
ratioAB(:,:,i)=A./B   % A and B are matrices for each Th

RF=ones(m,n);
for i=1:m
    for j=1:n
        Z2=Z(i,round(j));

col = find(Th > Z2,1,'first')-[1 0]
RF(i,j)= diff(cat(3,ratioAB(i,j,col)),[],3)/diff(Th(col))*(Z2 Th(col(1)))+ratioAB(i,j,col(1));

    end
end

[Jan]

What is the difference to the thread http://www.mathworks.com/matlabcentral/answers/46453-how-to-ignore-values-in-a-matrix-that-is-out-of-bound-when-performing-column-find-in-an-array?

Answer 1

[Mani]

use imhist and set the values as thresholds