Why "Accessing Image Sub-Regions"s array like that?

In this case, why output shows like that? means, why start specific number 156? and why value look like change randomly?

Answer 1

[DGM]

Those are literally the pixel values in the image. There is no designed purpose for the first pixel of the image to be 156. It merely represents the intensity of light captured by the camera at that location, on a scale relative to a black level of 0 and a white level of 255. Open the following image in a new tab and zoom in on it.