From Daniel Grotta and Sally Weiner at PC Magazine
Pushing the old adage that more is better, most manufacturers market their newest digital cameras by touting how many more megapixels they have than previous or competing models. By this logic, a 4MP digital camera can’t possibly be as good as one with 5MP, and an 8MP unit has to be better than a 6MP model. Right?
Wrong. Megapixels are a measure of quantity (the amount of data captured), not quality. A digital camera’s image quality is based not on a single component, but on an entire system. True, the heart of the system is the image sensor, with however many megapixels, but that’s only part of the equation of how image quality is achieved.
Some of the other issues that influence image quality are pixel size, chip material, lens quality, and the ADC which converts the light signal to digital.
Plus a really good monitor might display 1600 x 1200. That means 1600 pixels across and 1200 down, do the math 1600 times 1200 = 1,920,000. Less than two megapixels. So if you take a “Hi Res” seven megapixel image about 72% of it is tossed out when the image is displayed.
I take dental photos at one to two mega pixels. That is the “low res” setting on most new cameras.