Getting Index exceeding matrix dimension for extraction the ROI

I took two image sequence,frame subtraction is applied and got the detected region by choosing the largest blob.Now I want to extract the ROI.My code works well if the detected window is bigger but doesn't work for smaller region.May b the subImage part has some error.Anybody can help me out. Thank you

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if true

clc; close all;

rgbImage1 = imread('C:\Users\ASUS\Desktop\Project\Frame\Frame3.jpg');

rgbImage1 = imresize(rgbImage1,[512,512]);

[rows, columns, numberOfColorChannels] = size(rgbImage1);

subplot(2, 3, 1);

imshow(rgbImage1, []);

rgbImage2 = imread('C:\Users\ASUS\Desktop\Project\Frame\Frame4.jpg');

rgbImage2 = imresize(rgbImage2,[512,512]);

[rows, columns, numberOfColorChannels] = size(rgbImage2);

subplot(2, 3, 2);

imshow(rgbImage2, []);

diffImage = abs(double(rgbImage1) - double(rgbImage2));

thresholdValue = 60; mask = diffImage > thresholdValue; mask = any(mask, 3); mask = all(mask, 3);

subplot(2, 3, 3); imshow(mask, []);

BW2 = bwareafilt(mask,3);

subplot(2, 3, 4); imshow(BW2);title('Foreground'); rp = regionprops(mask, 'BoundingBox', 'Area'); area = [rp.Area].'; [~,ind] = max(area); bb = rp(ind).BoundingBox;

subplot(2, 3, 5);

imshow(rgbImage2); rectangle('Position', bb, 'EdgeColor', 'red');

subImage = rgbImage2(round(rp(ind).BoundingBox(2):rp(ind).BoundingBox(2)+rp(ind).BoundingBox(4)),round(rp(ind).BoundingBox(1):rp(ind).BoundingBox(1)+rp(ind).BoundingBox(3))); subplot(2, 3, 6); imshow(subImage); end