How does the function imresize(matrix, [length, width]) work to rescale a figure?

I am trying to do binning of pixels in several images. I wanted to use this function, but I do not understand if it is working properly. To check the way the function works, I tried this: a = [1 2 3; 4 5 6; 1 2 3] and imresize(a, [2,2]) which gave me [2.4074 3.8426; 2.4074 3.8426]. I also tried b = [1 1 2 2; 1 1 2 2; 3 3 4 4; 3 3 4 4] and imresize(b, [2,2]) gave me [1.1992 2.0664; 2.9336 3.8008]. I really do not understand how matlab calculated these numbers.