Sorry if this question is not serious. I was discussing this with the friend and we had different opinions. I'd think others want to throw in their opinions. The question is:
What will be typical pixel count of digital camera 8 years from now ?
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The pixel count keeps going up even when most knowledgeable people think its enough. This is because megapixels is still equated to image quality in the mind of typical consumers. 8 years ago cameras where in the 3-6 MP range. This year they are mostly in the 12-16 MP range. Another 8 years we may see another doubling or tripling, so 24-48 MP is possible for compact digital cameras.
While per-pixel quality has gone seriously down, the increase in resolution has reasonably compensated for that, so the output quality of today's top cameras at a given print/display size is still better than those of a few years back.
Camera makers cater to all levels of consumers and you will notice that Canon, Nikon, Panasonic and Olympus all have produced high-end models with fewer megapixels than their predecessors in the last few years. For example, the advanced Nikon P7000 has 10 MP while the P6000 had 14 MP. Same thing happened in Canon G-series.
There is an immutable force which is going to limit how far megapixels can go without increasing sensor size and that is diffraction. Some cameras already have lenses that cannot open sufficiently at the telephoto end for their full resolution to be resolved. More and more cameras now use ND filters to simulate smaller apertures not to lose image quality.
This means we are likely to see sensors get gradually bigger at the low end to accommodate more megapixels. At the same time, more system with intermediate-sized sensors like the Nikon 1 should appear. At the density of today's compact camera, a Nikon 1 could have the same image quality with 64 megapixels!
There are reasons to want extra pixels even if per pixel noise increases, as until you hit the diffraction limit your overall resolution still increases when you increase sensor resolution...even when lens resolution remains fixed.
The ultimate limit is diffraction, as Itai states. Light passing through an aperture spreads out slightly. When your pixels are so small that this spread causes points of light to spread over several pixels then you don't gain any resolution from the extra pixels.
Diffraction limits the size of pixels, thus the actual pixel count is limited by both diffraction and sensor size. So large sensor DSLRs will be able to accommodate many more pixels than small sensor compacts.
So what is the diffraction limit? Well it depends on the aperture, and on the wavelength of light. Red light diffracts less so if you couple that with an aperture of f/1.2 and run the numbers you end up with hundreds and hundreds of megapixels. However few would be satisfied with a sensor that needs perfect f/1.2 glass, so the theoretical limit isn't all that useful.
Whilst the prevailing view is that megapixel counts are inflating wildly across the board, at a glance pixel counts in compacts seem to have stabilized. A brief look at Canon compact offerings from the last three years reveals a strong trend: 12 megapixels. This provides a better clue to what sort of pixel densities are actually practical.
Taking the 'enthusiast' compact Canon G12 as an example of the performance ceiling of small pixels and extrapolating the figures gives the following approximate limits:
So we're a long way off the sort of densities deemed workable in compacts!