Let's see if I understand what you're trying to do. As I understand it, you have a 512x512 matrix with lots of values of 98 on the left side and lots of 900 on the right side. And you want to automatically find the most common number on the left side of the matrix, and the most common number on the right side? Here's how I'd do that:
M = 1000*rand(512); % some random numbers between 0 and 1000
M(1:10:1e5) = 98; % every tenth value on the left side is 98
M(2e5:12:end) = 900; % every 12th value on the right side is 900
imagesc(M) % displays the matrix
It's difficult to see, because only 1 in 10 values on the left side ar 98, but still 98 is the most common value on the left side. And on the right side, the most common value is 900, because it's every 12th value. Here's how you'd find the most common value on the left and right side:
LeftSide = mode(M(:,1:256),'all')
RightSide = mode(M(:,257:end),'all')
