Samsung Galaxy S III(Credit: CNET)

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.

Note: As always with this column, if you already consider yourself an expert, then this article is probably not for you.

Shot with the Nokia 808 PureView.(Credit: Nokia)

Key ingredient #1: Sensor
Most budding and professional photographers will tell you that the most important ingredient in the optical system is the sensor, because that’s that’s the part that captures the light. The sensor is essentially the “film” material of a digital camera. No light, no photo.

Light enters through the camera lens, then passes to the camera sensor, which receives the information and translates it into an electronic signal. From there, the image processor creates the image and fine-tunes it to correct for a typical set of photographic flaws, like noise.

The size of the image sensor is important, and generally, the larger the sensor, the larger your pixels, and the larger the pixels, the more light you can collect. The more light you can catch, the better the image.

The experts I spoke to for this story had colorful ways of describing the relationship between pixels and sensors, but “buckets of water” or “wells” were a favorite intentionally oversimplified analogy. Imagine you have buckets (pixels) on a blacktop (sensor). You want to collect the most water in those buckets as possible.

To extend the water-and-bucket analogy, the larger the sensor (blacktop) you have, the larger the pixels (buckets) you can put onto it, and the more water (light) you can collect. Larger sensors are the reason that 8 megapixels from a digital SLR camera are better than 10 megapixels from a smartphone camera. You have the same number of pixels, but those pixels on the DSLR can be larger, and therefore let in more light. More light (generally) equals less-noisy images and greater dynamic range.

The fallacy of megapixels
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.

Usually, when you use the digital zoom on your phone, you’re blowing up and cropping in on an image to see each pixel up close. You all know what that can look like: grainy, blocky, and not always as sharply focused or as colorful as you’d like.

In the 808 PureView, Nokia uses a process called “oversampling,” which — for the PureView’s 5-megapixel default resolution — condenses the information captured in seven pixels into one (they call it a “superpixel.”) If you zoom in on an object, you’re simply seeing part of the image that’s already there, rather than scaling up. This method shouldtranslate to higher-resolution digital print-outs and zoom-ins than you’d normally see.

The technology in PureView has been five years in the making, Nokia’s Alakarhu said. Not only does PureView lean on the physical size of the sensor (specifically 1/1.2-inch), there are also custom algorithms on top of the sensor to adjust the image to reduce imperfections like noise.

As CNET’s Goldman has pointed out, this is an unusually large sensor for a smartphone, and it’s also larger than sensors found on the vast majority of point-and-shoot cameras.

The HTC One X and its siblings share an image processor separate from what main CPU and GPU.(Credit: CNET)

Key ingredient #2: Image processing
In addition to the size and quality of the lens and sensor, there’s also the image processor. Most modern high-end smartphone CPUs have dedicated graphics processors built into their chip, which, being hardware-accelerated and not just software-dependent, can quickly render images like photos, videos, and games without overtaxing the main application processor.

At Mobile World Congress, HTC touted a discrete image processor for its HTC One family of phones, called the HTC ImageChip, that is capable of continuous pictures at a rate of 0.7 seconds between shots. The chip, which lives in the HTC One V, HTC One S, and the global version and both US versions of the HTC One X, is significant in providing a unified level of photo performance between the three models, whose other features differ quite a bit.

The separate processor also explains how HTC can claim those shot-to-shot times on both the global HTC One X that runs on Nvidia’s Tegra 3 processor and the U.S. version that runs on Qualcomm’s Snapdagon S4 processor.

I promised that there was software bridging the hardware and the final image, and there is. Algorithms and other logic are what create the final image output on the phone’s screen. This where the most subjective element of photography comes in — how your eye interprets the quality of color, the photo’s sharpness, and so on.

The image processor is also what helps achieve zero shutter lag, when the camera captures the photo when you press the capture button, not a beat or two after.

Wait, there’s more
There’s much more to know about the competing technology that goes into sensors, but backside-illuminated sensors are starting to be used much more in smartphones. This type of sensor is often synonymous with better low-light performance because it increases photosensitivity. However, if you shoot in bright light, it can also blow out your image. Here are more details on how backside illumination works.

The camera’s sensor size and image processor may be the most crucial elements for creating quality smartphone photos, but other considerations come into play. Higher quality components, for example, can help tease out better photos, but they could also cost more, which could lead to a marginally pricier camera.

While the total cost of a camera module is only one part of the total cost, Gartner analyst Jon Erensen said that high-end parts could double the price of a basic camera set, and thought that parts could cost $15 per phone. The smartphone makers I contacted for this article, like Samsung and Nokia, wouldn’t share sourcing or pricing information.

Windows phones like the Nokia Lumia 900 have physical buttons that wake up the camera even when the phone is locked. iOS and Android phones often use software shortcuts from the lock screen.(Credit: Josh Miller/CNET)

Usability is king
Despite the intense engineering focus that goes into the camera’s physical elements, both Nokia’s Juha Alakarhu and Samsung’s Drew Blackard, senior manager of product planning, stress the importance of the customer’s experience — how easy is it to open the camera from a locked position, how fast do photos capture, how desired are the special effects and shooting modes?

For HTC’s part, the manufacturer includes extra logic in some phones, like the Amaze 4G, that detects smiles and auto-surfaces photos it considers the most technically proficient. Samsung is also starting to advertise similar qualities in the Galaxy S III’s camera software.

For most phone owners, said Samsung’s Blackard, being able to quickly and easily share photos on the fly is far more important than pixel count. Just look at Instagram’s runaway success in sharing simple, small photos.

Gartner analyst Jon Erensen agrees. “What do you actually gain from going higher than you need, in a practical sense?,” he said, adding that most people upload smartphone photos to an online album like Google Photos or Facebook, or e-mail them to family and friends, formats that require many fewer than 8 megapixels, or even 5.

A recent trip to Indonesia illustrates what Nokia’s Alakarhu and the others mean by the whole experience taking precedent over the specs. While trekking with 22 pounds of gear on his back — including a high-quality DSLR — Alakarhu repeatedly reached for the Nokia 808 PureView he kept in his pocket. Although he considers himself an amateur photographer who will put in the time to frame a great shot, Alakarhu said he found himself using the PureView more because of its easy availability and quick start time when he didn’t want to take the time to set up a more involved shot on his digital camera.

I have my share of similar stories, and I suspect that you do, too.

We shouldn’t scrap pixel count entirely when weighing smartphone cameras, but in terms of the hardware and software details that actually go into making a great photo, megapixels are highly overrated. It’s high time we focus on other areas that count more, like that undersung sensor.

Thanks to CNET Senior Editor Josh Goldman, who contributed to this story.

Smartphones Unlocked is a monthly column that dives deep into the inner workings of your trusty smartphone.