image size "power of 2"?

if i load a sprite in Blitz3D - it resize my loaded texture image to a default size: 16,32,64,128,256 etc - all power of 2...

i checked pixmap.width/height in BlitzMax - it return 'perfect' image size... but - how many memory take a 80x80 image?

use it 80x80 pixels or full 128x128 pixels internaly?