OpenKinect/libfreenect — comment on commit aed02623ddf99f4b2115d88d7b9c0afea4e2cbdb
File:  line 0
By zarvox:

Argh, you're right. I compared the 1280x1024 RGB image with the 640x480 one and see that the 640x480 one does indeed crop the bottom, so the pixels keep their aspect ratio. And your analysis is spot on.

Fixed in 73a22aff094b4e7245a5217677dc52db0ba56a88.