Say an image sensor has an array size of 1280 x 800 pixels. Its specifications state that it has output support for the following resolutions: WXGA (1280 x 800) and VGA (640 x 480).
My question is the following: If we choose to output images in the VGA format, which part of the original 1280 x 800 array is the 640 x 480 extracted from? Is it taken from the middle? Is it just a sub-sampled (or averaged) version of the original array?
[Optional follow-up: Note also that the aspect ratios of the two resolutions are different; could that have an effect on the camera's intrinsic parameters (i.e., pixel size, aspect ratio, principal point) when choosing the smaller resolution?]