No...that's wrong :) the electron gun doesn't just display 256 distinct levels of a nuance....it can display many more...it's an "analog" device, works by changing tiny amounts of current. If you talk about pixels we must only think of how they are STORED on the computer. An 8 bit greyscale (so single channel) image, can hold 256 distinct levels of information (2 to the 8th power) A 16 bit greyscale image can hold 65 536 distinct levels of information (2 to the 16th power) If you don't believe it, make a new 16 bit greyscale image in PS. First make a smooth gradient (black to white) lets say horizontally, then take a big very smooth brush, set it to a nuance of grey and paint a little. Now zoom in and convert the image to 8 bit and see what happens.