Try this:
% Demo to find 4x4 regions with the highest sum value.
clc; % Clear the command window.
fprintf('Beginning to run %s.m ...\n', mfilename);
close all; % Close all figures (except those of imtool.)
imtool close all; % Close all imtool figures.
clear; % Erase all existing variables.
workspace; % Make sure the workspace panel is showing
fontSize = 15;
% Get temperature array with temps between 20 and 30 degrees celsius.
grayImage = 20 + 10 * rand(360, 576);
subplot(2, 1, 1);
imshow(grayImage, [])
impixelinfo; % Let user see RGB values as they mouse around.
colorbar
axis('on', 'image');
title('Original Image', 'FontSize', fontSize);
% Maximize the window to make it easier to draw.
g = gcf;
g.WindowState = 'maximized'
fprintf('Done running %s.m ...\n', mfilename);
% Get kernel
kernel = ones(4, 4);
sumImage = conv2(grayImage, kernel, 'same');
subplot(2, 1, 2);
imshow(sumImage, []);
axis('on', 'image');
title('Sum Image', 'FontSize', fontSize);
% Find 5 highest sums
sortedValues = sort(sumImage(:), 'descend');
[highRows, highColumns] = find(sumImage >= sortedValues(5))
% Place red squares around those areas.
hold on;
MarkerSize = 30;
plot(highColumns, highRows, 'rs', 'MarkerSize', MarkerSize, 'LineWidth', 3);
