Thanks for all who contributed to this question.
My view is that it is difficult to answer this question without getting technicality involved. First of all, resolution is not a direct function of number of pixels but depends on a number of factors. The size of the sensor (CCD, CMOS) is another factor. Due to the nature of light (which behaves both as electromagnetic waves and particles), a typical sensor consists of millions of receptors of protons. To capture colour, a filter is used for each receptor to receive a particular colour of light (e.g. green filter for receptor to receive green light proton). As human eyes are more acceptable to green colour, there are more green receptors than red and blue receptors in a given sensor.
This makes very interesting result. Consider this: what will happen if a green proton falls onto a blue receptor? Absolutely nothing! In a sense, that green light signal is lost. Hence each receptor does not make a pixel but rather a pixel is obtained by interpolating a number of receptors.
Another aspect of the receptor is that light particles behave in the manner described by quatum physics. In essesnce, if one conducts a number of experments with the same light intensity, the number of protons received by each receptor will vary slightly, following a certain probabilistic distribution. Hence it is the statistical average that we report for a given situation as one can never predict with certainty the eact number of protons for a given receptor.
Given such a situation, even optical lenses add to the complexity, Vgoogle has some very technical lectures on this topic as well.
However, it is still possible to make very rough and simplified calculation. For example someone has made the following comment on Canon EOS 5D DSLR - commenting on sensor size and resolution:
"Additionally the 5D's 12.8 Megapixel resolution matches the theoretical detail of a 3000 dpi 35mm film scan which, coupled with the full-frame coverage, makes it a viable replacement for die-hard 35mm owners" (
http://www.cameralabs.com/reviews/Canon5D/index.shtml)
I hope I have shed some light on the subject. Interesting though it may be, but is is really difficult to compare resolutuoion in a simplistic sense between a digital system and an anolog system (film).
