the physical size of the ccd array also helps determine the sensitivity of the overall array and thus it's true resolving power. Too small of an array will be poor in low light and provides more digital noise.

The cells in a ccd array gather light and sum the intensity over time (a short time!) As a digital cell is operated closer and closer to its threshold value (the point where it can just differentiate light from no-light) there is a finite chance that the cell will be influenced by the surrounding electronics that make it function This may cause the cell to report a higher than true value. This happens most often in the shadow areas of under exposed images and appears as random color spots in dark areas. Since the blue sensor cells (Bayer pattern) are the least sensitive, the "Noise" more often appears as a green- yellow component. (Lacking the needed blue.)

Noise increases as you turn up the effective ASA (film speed) of the sensor. Your are trying to operate closer and closer to this threshold value. Larger sensor arrays with larger individual cells are effected less because they "see" more light area striking them. There is more overall intensity and thus they more easily differentiate the threshold.

So what are todays camera resolutions?

Most people tend to forget that the reason for making a large print is actually to increase the acceptable viewing distance (change the audience experience). A 4"x5" print is great in a book, but only one or two people can get around the book to view the image at one time. A 4"x5" print makes a really poor billboard! It is hard to see from a moving car. (A different audience.)

Yes you can put your nose on an 11"x14" and claim to see the grain and noise, but is this same thing apparent at proper viewing distance (several feet from the print?) An 11" x 14" print is not intended for hand holding, it is intended to let more people see it from a comfortable distance. Too often I have hear that all prints need to be printed near the best resolution of the printer. To that I say bunk!

I am including a multi-page write up (=>a pdf file<=) that goes into far more detail on how many pixels you need to achieve desired output. You will find it is also based on the "method" of final display ... monitor, lcd, monotone print. color print, etc. Eventually I will update this write up and add it to these WEB pages, but for now you can download it and read it if interested. It describes in far more detail the workings of printers, monitors, and how they effect the final output.