Halving the DPI in each direction (vertical and horizontal) means you end up with only a quarter of the pixels: 0.4 megapixels instead of 1.6 megapixels.
I thought they were 300dpi panels, but that the dpi was halved in color mode? I'm curious what color filters they have. Perhaps each 2x2 pixel has 3 filtered dots (RGB) and one fully transparent dot?
It's generally halved, i.e. the display is 300dpi in mono mode, but 150dpi in color mode.