As the Ars team convenes for two days of meetings in Chicago, we're reaching back into the past to bring you some of our favorite articles from years gone by. This story originally ran in March 2009.

Akira Watanabe, manager of Olympus Imaging's SLR planning department, has officially thrown down the gauntlet and drawn a line in the megapixel sand. "Twelve megapixels is, I think, enough for covering most applications most customers need," he told ZDNet this week at the annual Photo Marketing Association convention. But is he right?

The megapixel myth

Megapixels are the digital camera market's equivalent of horsepower and megahertz—a single metric that consumers and marketers latch on to tenaciously, despite the fact that it hardly describes overall performance. Over the last several years, camera manufacturers have been pumping up the megapixels on each successive camera model, regardless of whether such increases offered any real benefits (hint: they usually did not).

See, throwing more megapixels at the digital imaging problem is akin to bumping up the processor speed on a motherboard with a slow bus and small amounts of RAM, or adding a turbo to a small engine on a car with lousy brakes and wobbly suspension. The number of megapixels in a camera's image sensor is just one in a number of aspects that truly define how well a camera works.

In an image sensor, larger pixels mean better light-gathering capability. This translates to better low-light performance, better color accuracy, and in some cases better dynamic range. Sensors commonly come in a few different sizes: Full frame (24 x 36mm), APS-C (17 x 25mm), Four-thirds (13.5 x 18mm), and even smaller sensors on compact point-and-shoot models. As manufacturers cram more pixels on a given sensor, those pixels get smaller and smaller.

Throwing more megapixels at the digital imaging problem is akin to bumping up the processor speed on a motherboard with a slow bus and small amounts of RAM, or adding a turbo to a small engine on a car with lousy brakes and wobbly suspension.

Typically, this reduction in individual pixel size on a sensor reduces its ability to gather light, reducing its sensitivity. Now, manufacturers have devised a number of technologies to try and combat this problem, but jamming more and more pixels on a sensor quickly leads to diminishing returns in terms of image quality.

How many megapixels is enough?

The truth is, though, that 6MP is enough to make a very nice 8 x 10" print—in fact, I've seen very nice, though soft, 8 x 10" prints from early 3MP DSLRs. More pixels can mean larger prints or more room for cropping. But who's making larger prints, other than professionals? And with compact cameras offering up to 24x zoom ranges, exactly how much cropping would someone need?

"I personally believed, before starting the E-System, that 12 was enough," Watanabe said. "We interviewed many professional photographers, people in studios, about how many they needed in the future. Before we started the system, we had a rough idea we'd be at a plateau at 12 megapixels."

That figure, 12MP, is a pretty good limit for a majority of serious photographers. A large majority of professional portrait, event, and wedding photographers are using cameras in this range. But Watanabe doesn't mean to suggest that there aren't photographers with more demanding needs. "We don't think 20 megapixels is necessary for everybody. If a customer wants more than 12 megapixels, he should go to the full-frame models," he said.

And for casual users, whose images largely end up on sharing sites like Flickr, Picasa, or PhotoBucket, even 12MP is overkill. With a decent lens, something in the 6-8MP range will more than suffice. Keep in mind that with the increase in megapixels comes a resulting increase in file size. So shooting hundreds or even thousands of 12MP images means larger memory cards, more space eaten up on hard drives, and more time sorting and editing—all for images that are likely to end up viewed at no larger than 800 x 600px... or about half a megapixel.

Beyond megapixels

Along with the number of megapixels in a sensor, other factors affect the image quality of a camera. The dynamic range, or the range of tones the sensor is able to reproduce, is a rather important one. A high-pixel-density sensor's ability to perform well in low light, which we mentioned above, is another. But beyond the sensor itself, the two other major factors that come into play are the on-board image processing hardware and the camera's lens. This is one reason SLRs have had a resurrection of sorts lately: DSLRs offer better lenses, larger sensors, and often better image processing.

So, manufacturers are starting to focus more on features like wider or longer zooms, higher-quality lenses, low-light performance, dynamic range, and high-def video capabilities. We've already seen a pretty significant competition between Nikon and Canon for the high-ISO crown this past year or so, and the improvements gleaned from high-end DSLR designs are trickling down to compact cameras. Further, Fuji has recently begun focusing marketing on dynamic range with its new EXR sensor technology. And some compacts, such as recent Pentax and Canon superzoom models, as well as DSLRs, like the Canon EOS 5DmkII or Nikon's D90, have already begun to exploit digital sensors to capture HD video.

Though focusing solely on the number of megapixels made marketing and buying digital cameras easier, it seems that we are at a major turning point in the direction of further developments in digital camera technology. Much like cars have shifted from horsepower to safety and efficiency, and computers have shifted from mega- (and giga-) hertz to multiple cores and... well, efficiency, digital cameras will shift toward other aspects that reflect the "bigger picture" of a camera's performance.

Further reading