Creating an image of first non-zero values in a 3d matrix

Hi everyone,

I have a 2300x2475x109 datacube/ 3d matrix (109 images with 2300x2475 pixels). All images are binary (0 and 1). Now I want to create an image where each pixel contains the index of the first non-zero value. So for example, if the pixel 500x1500 is always zero until to the 12th image, the value in the result image should be 12. I could write a code, where this works for a single pixel location:

pixval = im_datacube(500,1500,:);
 pixval = squeeze(pixval);
firstNonZero = find(pixval~=0, 1, 'first');

But now I want to make that for each pixel location and merge it all together into a single image. I tried to do it with loops, but i failed so far. Hope you can help me, thanks in advance.

Answer 1

[Bruno Luong]

[maxval,firstNonZero] = max(im_datacube ~= 0, [], 3);
firstNonZero(~maxval) = NaN; % pixel where 1 is not found along the 3rd dim 

firstNonZero

[Simon Hagmayer]

It worked, thank you so much.

[Simon Hagmayer]

Do you also know how to create the image with the last non-zero index values? I know the max() function only takes the first index of the values appearance, so I tried to do it with find(), but I could not get it to work so far...

[Bruno Luong]

Flip the 3rd dimension of the input array; find the first indexes on flipped arrays using MAX as above, then reverse the indexes found.

[Simon Hagmayer]

A very elegant and simple solution, thank you so much.

Answer 2

[Guillaume]

One way:

inverted_image = ~im_datacube;
max(cumsum(inverted_image, 3) .* cumprod(inverted_image, 3), [], 3)