Camera megapixels: Why more isn't always better (Smartphones Unlocked)

It's time to forget megapixels as the measure of smartphone camera performance and pick a new yardstick.

Just days ago, Samsung announced the Samsung Galaxy S III, the global, quad-core, Android Ice Cream Sandwich successor to its best-selling smartphone ever, the Galaxy S II.

CNET readers' reactions were mixed, with several comments that the 8-megapixel camera didn't seem too hot.

Rumors of a 12-megapixel camera leading up to the announcement were partly to blame. It's no wonder that some felt that a perfectly good 8-megapixel spec was taking a step back, especially with the 16-megapixel shooter on the HTC Titan II out in the wild, and Nokia's 41-megapixel 808 PureView, a Mobile World Congress stunner.

Despite the fact that 8 megapixels is pretty standard for a high-end smartphone camera these days, one CNET reader described the Samsung Galaxy S III's camera as "so last year." Never mind that at least one high-end phone, like the Samsung Galaxy Nexus, still touts a 5-megapixel camera.

It isn't that 5-megapixel cameras can't be good, even better than phones with an 8-megapixel count lens; or that we're due for another bump along the megapixel scale. It's that to many shoppers, 5 megapixels just doesn't sound as good as 8, even if the camera produces terrific, knock-your-socks-off shots. And well, if 8 is good, then 12 is better.

The dirty secret lurking behind today's 8-megapixel yard stick for high-end status (and what any photography nut will tell you) is that the megapixel number alone is a poor way to predict photographic performance.

For instance, the original Samsung Focus took some lovely shots on its 5-megapixel camera, while the Motorola Droid Razr's 8-megapixel lens creates disappointing pictures. And the 5-megapixel camera on Apple's iPhone 4 beat out some 8-megapixel cameras on the market and delivered good low-light results.

Of course, that's not to say that bigger can't also be sometimes better. For instance, HTC's One X high-performance 8-megapixel smartphone camera boasts rapid shot-to-shot action, and its Titan II takes 16-megapixel shots of solid quality.

So what's the formula for fantastic photos? It involves an entire camera module that includes not just the size and material of the main camera lens, but also the light sensor behind it, the image processor, and the software that ties it all together.

Camera megapixels: Why more isn't always better (Smartphones Unlocked)

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The fallacy of megapixel - megapixels camera

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You can start to see that cramming more pixels onto a sensor may not be the best way to increase pixel resolution.

Jon Erensen, a Gartner analyst who has covered camera sensors, remembers when the cell phone industry jumped from 1-megapixel to 2-megapixel sensors.

"They would make the pixel sizes smaller [to fit in more pixels]," Erensen told me over the phone, "But keep the image sensor the same." Erensen similarly used the water analogy, this time swapping "buckets" for "wells."

What ended up happening is that the light would go into the well and hit the photo-sensitive part of the image sensor capturing the light. So if you make the wells smaller, the light has a harder time getting to the photo-sensitive part of the sensor. In the end, increased resolution wasn't worth very much. Noise increased.

The relationship between the number of pixels and the physical size of the sensor is why some 5-megapixel cameras can outperform some 8-megapixel cameras, and why we may not see, or want, a 12-megapixel camera on a smartphone. A slim smartphone limits the sensor size for one, and moving up the megapixel ladder without increasing the sensor size can unnecessarily degrade the photo quality by letting in less light than you could get with slightly fewer megapixels.

Then again, drastically shrunken pixel sizes aren't always the case when you increase your megapixels. HTC's Bjorn Kilburn, vice president of portfolio strategy, did share that the pixel size on the 16-megapixel Titan II measures 1.12 microns whereas it measures 1.4 microns on the One X's 8-megapixel camera. CNET's Josh Goldman points out that this is a small pixel size; however the take-away in terms of this discussion is that the two similar sizes mean that photo quality should be comparable at a pixel-by-pixel comparison.

Unfortunately, most smartphone-makers don't share granular detail about their camera components and sensor size, so until we test them, the quality is largely up in the air. Even if smartphone makers did release the details, I'm not sure how scrutable those specs would be to the majority of smartphone shoppers.

For more information on the interplay between megapixels and sensors, check out the excellent description in CNET's digital camera buying guide.

What about Nokia's 41-megapixel PureView?

Nokia's story behind its 808 PureView smartphone is really interesting. CNET Senior Editor Josh Goldman has written one of the best explanations of the Nokia 808 Pureview's 41-megapixel camera that I've seen. I strongly suggest you read it.

In the meantime, here's a short summary of what's going on.

Juha Alakarhu (pronounce his first name YOO-hah), is head of camera technologies at Nokia, where he works within the Smart Devices team. Alakarhu explained to me that although Nokia has engineered the PureView to capture up to 41-megapixels, most users will view photos as the 5-megapixels default.