maximum value in a 3d matrix

write a MATLAB script that finds the maximum value and its M and N indexes in each of the P pages.  (i.e. the max on EACH of the pages, not the single max among all the pages. You will find P maxima and P pairs of indexes.

This is a 3d matrix (m*n*p) and i want to find the maximum value on each "page", as well as its m by n indexes on each page. can anyone please help?

[Bola]

i would also like to plot m*n of the maximum values on each page.

[Image Analyst]

What does that mean? If you have a 640*480*3 array, you want to "plot" 640*480 = 307,200 points? How are you getting those 3 hundred thousand points? Or do you want a 640*480 array of the max value from each page? (That would be like an image and you could use image() or surf() to visualize it.)

[Bola]

no,lets say if i have a 100*100*100 array and i find the largest value on each "page" that would mean i have 100 numbers. If i find the indexes of those 100 numbers i have 100*100 numbers i would like to plot those indexes

[Image Analyst]

Assuming "page" means a "slice" or "plane" in the "z" (third) dimension, then for each "page" you'll have one or more max values. Let's say you have only one per page just to make it easy. So you have 100 maxes. And each max element will have an x, a y, and a z index. So you can store these in a 100 by 4 array where each row is

[maxValue, x, y, z]

So that's 100*4 = 400 values, or 300 if you're not including the values of the element and just record the x,y,z values, or even 200 if you just have 100 rows and the x and y locations for that row (where the row is the page number). So how do you get 100*100 = ten thousand values?

So, assuming you have the 100 locations (300 x,y,z values) how do you want to plot them? With plot3() or scatter3()?

Answer 1

[Azzi Abdelmalek]

for k=1:size(A,3)
   a=A(:,:,k);
   [maxv,idx]=max(a(:));
   [ii,jj]=ind2sub([size(A,1) size(A,2)],idx);
   out{k}=[maxv ii jj]
end
celldisp(out)

[Bola]

thank you, this works beautifully, but i would also like to now plot ii against jj. When i do so, i get a blank graph.

Answer 2

[Andrei Bobrov]

s = size(A);
[v,ii] = max(reshape(A,[],s(3)));
[i1 j1 ] = ind2sub(s(1:2),ii);
out = [v;i1;j1;1:s(3)]';