"Actual pixels" means what it says -- one pixel in the image is one pixel on
the monitor. No interpolation taking place, so a good way to judge an image.
But what do you mean by "efficiency"? Whether the camera focuses correctly
or how sharp is a correctly focused image? The latter is a very complex
topic, and not something that you can easily measure at home. Results will
depend on the lens quality, aperture setting, the low pass filter in front
of your sensor and the camera's image processing.
Unless you are taking a picture of a flat object, there is only one distance
that's in focus, and the rest is, by necessity, blurred to some degree. How
much depends on the focal length, the distance to the object and the
aperture (f #) setting.
A simple test for correct focusing is to arrange three cereal boxes (or
similar flat objects with fine print and some color), with the one on the
left 1" in front of the one of the center, and the one on the right 1"
behind. Open the aperture to the maximum (lowest f #), zoom or position the
camera to have all three boxes in the image, select a single point center
focus and place it on the center box. In the image you should see the center
box sharp and the other two blurred. If the left or the right box is the one
in focus, the focusing mechanism needs adjustment. Make sure your camera is
set to its highest resolution and lowest compression (if you are using JPG).