What is the Depth Resolution difference between 640*480 & 1280*800

[YLChang]

My stereo camera is Obbrec stereo astra s.
I used OpenNi SDK to get depth image. I would like to know why the depth resolution under 640 * 480 looks more precise than 1280 * 800.
This is 1280p image

Does Depth under Resolution 1080 has undergone any post processing?
Thank you.

[wujood]

This could be due to the fact that the stereo astra s has a depth frame resolution of "640×400@30FPS". Maybe the sdk resizes the image and therefore produces a softer image?

EDIT:
The RGB frames have a resolution of "1920×1080@30FPS" or "1280×720@30FPS" , just in case if you are wondering why the resolution differs