为什么积分图像包含额外的行和列零？

I am learning how to use the integral-images using opencv with Java API, and i created a test that displays the grayscale image before using the integral-image and after using it. the grayscale image is 10 x 10, and when i converted it to the integral-image i found it 11 x 11 with extra rows of zeros and extra column of zeros as shown below in the output.I am learning how to use the integral-images us