The argument that you need 255 grains to represent 255 shades of grey is pure bullshit. Each grain is efectively one bit of infprmation - it can represent a 1 or a 0 (either its there or it isn't there) sor you only need 8 grains (or there abscence) to represent 255 shades of grey. In addition the positioning of these grains is not locked into a grid as in a CCD sensor.