Same MP, drastically different file size?

That makes sense. I just mentioned the setting as the "start with the obvious" of am I making sure that it's putting out the best pics it can. So on these small cameras (like on cell phones) the MP is actually a bit of a misnomer it seems.

About a year ago, we ran across a Chinese Trick in marking Megapixels on some cell phones with cameras.

If you read the specification sheet, it didn't say MP.
I believe it said "NP" or "nP".

After some searching, we found this was a little known measurement that meant 1/10th of a MP.
That would means a 5nP sensor was actually 0.5MP

..

I've checked this across enough stuff, and being Nokia as well, it's a legit 5MP, but that's a dirty little trick that I'm sure few people notice.

No doubt. I was asking because I figured that regardless of sensor size, to some extent pixels are a large determinant of file size, since the file size difference was so great. Last year when I was looking at an SLR, I found it interesting how Sony has 14.2MP on some of their Alphas that compete against the Nikon D90, but when you compare picture quality, those extra pixels on a similar sized sensor just result in noise. I totally agree- pixels are one of the great marketing gimicks.

As already mentioned, a JPG file will always be compressed to a certain extent but it looks like the phone is compressing it much more than your older camera - and probably loosing a lot of image data in the process.

As to the 10 mp camera being better than the 2 mp... I'm not so sure about that, I'm sure a few of the original dSLRs with a fairly low pixel count will be producing images of much higher quality than todays 14 + mp compacts are managing. My own old Nikon coolpix 775 (2 mp) still produces better images than my new Olympus compact does with 10.1 megapixels tp play with - even if the Olympus is waterproof.

Who will need more MP? I gave an explanation down there. I routinely print 13x19 (photo quality 300 ppi) at home for display, so I can fully use the 21 MP on my Canon 5D Mk II. For those who have a wide format 24 in printer at home and wants to do photo quality (300 ppi) A2 size (16.5 x 23.4 inches), then they can take advantage of the 39 MP of the medium format digital camera.

Sure you can do large prints with fewer MP. I have an old Canon 30D with 8MP and can still do 13x19 prints, but there is visible difference in fine details when looking at it closely. It is okay because this size prints are usually viewed at a distance. The professionals who charge people a lot of money for large prints however may want to make their prints look perfect even at close examination, and they can benefit from higher MP.

If you need/like to make prints larger than 8x10 routinely, then you should consider D-SLRs. Crowding too many MP in a small sensor of a compact PS will increase noise and lower photo quality. As I said earlier, most people do not need more than 8MP, which can make photo quality 8x10 prints. There are many factors that determine photo quality. Having a high quality compact like Canon G11 and S90, will have good image quality even at 10MP. Sensor technology has advanced a lot, there is no question about it. But camera quality varies widely. Two cameras with the same MP will not have the same quality, depending on other components. Underwater cameras have to make a number of compromises and are optimized for underwater conditions, which is very different from normal conditions. That is one problem with compacts, when the photographer leaves the settings and technical details to the camera.

Having more MP is not always bad. More MP in a compact PS is more of a gimmick than actual improvement. But having more MP in a full frame or medium format camera can be useful, especially for those who routinely do large gallery size prints or for studio/landscape work that has a lot of fine details. That is why Nikon has a D3x in addition to D3, and Canon has increased the MP on 5D Mk II and 1Ds Mk III. However an average consume will not likely need more than 8MP.

How many MP is needed depends on the print size of your photos. A 2MP camera can produce best photo quality for 4x6 prints, but still has good print quality up to 8x10. An 8MP camera can produce best photo quality for 8x10 prints, but still has good print quality up to 17x22 size. Having more MP in a small sensor compact or mobile phone will diminish the pixel size and increase noise. The 2MP camera may not have much room to crop for a 8x10 size print, but 5 MP is probably better.

sorry, the last sentence I meant to say, "..., but 8MP is probably better if you plan to do 8x10 prints." Photo quality is not just based on pixel number or pixel size/pitch. The lens, the sensor design, the processing engine, the AF system, the metering, etc, are all important in optimizing image quality. Understanding how each component affect image quality will help one make sensible choice. But camera is only a tool. The photographer is still the key to the photo quality.