Assigning multiple values of a 3d matrix to another matrix

I have the following problem. Say I have a 3D image stored in variable I and three 2D matrices that contains x,y,z points of interest as follows.

I = rand(10,10,10);
x = [3 4];
y = [5 6];
z = [1 2];

Now, I want to make a new variable Inew, which contains pixel intensities corresponding to these x,y,z positions.

Inew(1,1) = I(x(1,1),y(1,1),z(1,1));
Inew(1,2) = I(x(1,2),y(1,2),z(1,2));

How to perform this action without going through a 'for' loop that goes through point by point? In my actual problem, all these matrices are huge. I is 900 by 700 by 1000 and x,y,z are each 900 by 3600. Going through point by point is very time consuming.

In the given example, if I just say, 'Inew = I(x,y,z);' it will obviously give me an output that is of size 2 by 2 by 2, which is not what I want.

Any help will be great.

Answer 1

[Guillaume]

Use sub2ind to convert your x, y, z into linear indices:

Inew = I(sub2ind(size(I), x, y, z));

Answer 2

[sundar]

Great! Thanks for the solution :)