The total number of pixels [on an HDTV screen] is 1920 horizontally x 1080 vertically = 2,073,600 pixels. There are 256 possible intensities of red, green and blue for each pixel, so that's 2563 = 16,777,216 possible colors. To figure out how many possible images there are, we need to raise the second number to the power of the first, so 16,777,2162,073,600 = 1.5 * 101,4981,180 possible images. That's a pretty big number "“ it's almost a million and a half digits long. Printing it in 10 point Monaco would take over 2,700 pages of paper. Scientists estimate that there are 1080 atoms in the observable universe "“ a tiny number in comparison.However big it may be, the fact that the number is finite is a surprising thing to realize. It means that every possible image has a unique ID number. So instead of asking me, "did you see that picture of MIA performing pregnant at the Grammys", you might ask, "did you see image number 1,394,239,...,572?" Obviously that is totally impractical and it would make you a huge nerd, but it's interesting that you could.
More in the same vein at the link. I was surprised that the number of states a video screen could be in was so much larger than the molecules in the universe.