On a recent trip to Asia, I was browsing an electronics duty free store in Tokyo airport, chock full of the latest cameras. Not being able to read Japanese, the only recognizable characters in the displays were the numbers — the number of megapixels, for the most part.
And that made me think, because this figure has become so important to digital camera sales. More megapixels sounds like a great idea, because it means more resolution for your pictures — they’re clearer and can be made into larger prints – right? Well, not quite. It’s possible an older camera with fewer megapixels actually produces cleaner, more detailed pictures.
More megapixels are not necessarily better because of some physical constraints. The size of the sensor chip that collects the light and makes the image is fixed, so more megapixels means that the individual photo sites (pixels) on the sensor get smaller if more megapixels are added. This is a problem because, in general, smaller pixels mean more noise. Noise shows up like film grain in a picture – it’s a measure of the difference between the actual light level and that measured by the photo site. In other words, it’s an error in the light reading. Smaller sensors are prone to more errors for physical reasons that are complicated to explain… and I’m not going to go into that level of detail here. The net is that more megapixels mean smaller light sensor sites, and therefore more "grain" in your pictures.
Professional digital SLRs have “full frame” (i.e., 35mm-sized) sensors, which is one reason why professionals prefer them – the image is “cleaner” since there is less noise. So if this is the case, why the obsession with cramming more megapixels onto the sensor? In the early days of digital cameras, the manufacturers were able to reduce the noise level of the sensor sites at the same time as putting more of them into the same space, through better manufacturing and design technology. So there really was an improvement in the camera. We got used to more megapixels meaning better pictures. The problem is that this isn’t always the case any longer, and yet we expect the same improvement.
This is particularly the case for compact (palm-sized) digital cameras, which have teeny tiny sensor pixels. They’re made at the limits of chip manufacturing technology and adding more megapixels definitely means more noise – grainer pictures – for these cameras. Manufacturers include a lot of "noise reduction" software in the cameras to compensate, which reduces noise at the expense of making the pictures more blurry and lacking in definition (detail).
“Pro-sumer” SLR cameras, like the Canon 40D, are a different story. Here, Canon has been able to increase the quality of the sensor sites and the tiny micro-lenses that sit over them, so that going from 10.1 megapixels (40D) to 18 megapixels is accompanied by an overall reduction in noise. Yes, more megapixels but less noise. The question is whether this can continue for the follow up to the 50D that is inevitably in the works.
The net: when choosing a camera, especially a compact, consider whether it has too many megapixels by finding out how much noise and blurring (from noise reduction) there is in the final pictures. You might be better off with an older, cheaper camera with fewer megapixels. Check out a good review website like www.dpreview.com to find out how the camera's pictures perform versus the competition.