% determine possible combinations of tile sizes
clear all, close all, Nx=2880; Ny=2176; px=[]; py=[];
for i=2:(Nx/30)
  if mod(Nx,i)==0, px=[px i]; end
end
for i=2:(Ny/30)
  if mod(Ny,i)==0, py=[py i]; end
end
n=0;
for i=1:length(px)
  for j=1:length(py)
    n=n+1;
    pnx(n)=px(i);
    snx(n)=Nx/pnx(n);
    pny(n)=py(j);
    sny(n)=Ny/pny(n);
    pnxpny(n)=pnx(n)*pny(n);
  end
end
[pnxpny i]=sort(pnxpny);
pnx=pnx(i); pny=pny(i);
snx=snx(i); sny=sny(i);
[pnxpny' pnx' pny' snx' sny']


     npx*npy         npx         npy         snx         sny
         480          30          16          96         136
         510          30          17          96         128
         512          32          16          90         136
         544          32          17          90         128
         576          36          16          80         136
         612          36          17          80         128
         640          40          16          72         136
         680          40          17          72         128
         720          45          16          64         136
         765          45          17          64         128
         768          24          32         120          68
         816          24          34         120          64
         960          30          32          96          68
        1020          30          34          96          64
        1024          32          32          90          68
        1088          32          34          90          64
        1152          36          32          80          68
        1224          36          34          80          64
        1280          40          32          72          68
        1360          40          34          72          64
        1440          45          32          64          68
        1530          45          34          64          64
        1536          48          32          60          68
        1632          48          34          60          64
        1920          60          32          48          68
        2040          60          34          48          64