Thursday, February 14, 2013

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

A 16-megapixel smartphone camera sounds great, but an 8-megapixel shooter could still produce better pics.

Increasingly, the 8-megapixel smartphones camera standard you thought you knew will ratchet up to 13 megapixels for high-end phones.
In many products -- like this past January's Pantech Discover (12.6 megapixels), last October's LG Optimus G for Sprint (13 megapixels), and even last year's HTC Titan II (16 megapixels) -- we're already there.
And no, I won't forget to mention last February's Nokia 808 PureView, a 41-megapixel Mobile World Congress 2012 stunner that CNET camera editor Josh Goldman says is worth the hype.
Yet even though the technology exists, and some of it is even good, most best-selling flagship phones are, for now anyway, sticking to 8 megapixels -- like the Samsung Galaxy S3, the HTC Droid DNA, the BlackBerry Z10, and the iPhone 5. (The Nokia Lumia 920 nudges its sensor up to 8.7 megapixels.)
Shootout!: BlackBerry Z10 versus iPhone 5 versus Samsung Galaxy S3
In this lies the cautionary reminder (that photography nuts will tell you), that it's possible for an excellent 5-megapixel camera to produce photos you prefer over a shoddy 12-megapixel camera. The megapixel number alone is no guarantee of heightened photographic performance.
Instead, the formula for fantastic photos comes down to the entire camera module that includes the size and material of the main camera lens, the light sensor, the image processing hardware, and the software that ties it all together.
NoteAs always with this column, if you already consider yourself an expert, then this article is probably not for you.

Key ingredient No. 1: The sensor

Most budding and professional photographers will tell you that the most important ingredient in the optical system is the sensor, because 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 extremely important. In general, 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 you image can be.
Shot with a Nokia 808 PureView
Shot with the Nokia 808 PureView.
(Credit: Nokia)
The experts I spoke with 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) laid out 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 you have (blacktop), 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 best those 8 megapixels from a smartphone camera. You get roughly the same number of pixels, but those pixels on the DSLR get to 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. That hasn't stopped the cell phone industry from doing just that.
Jon Erensen, a Gartner analyst who has covered camera sensors, remembers when we collectively made the leap 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."

"What ended up happening is that the light would go into the well [the "bucket"] 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 8-megapixel cameras can outperform some 12-, 13-, or even 16-megapixel smartphone cameras.
There's more involved, too. A slim smartphone limits the sensor size for one, and moving up the megapixel ladder without increasing the sensor size can 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, shared that the pixel size on the 16-megapixel Titan II measures 1.12 microns, whereas each of the One X's 8 pixels measures a slightly larger 1.4 microns.
As a result, the photo quality on both these HTC smartphones should be comparable at a pixel-by-pixel level.
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 (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 808 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.
LG Optimus G
Sprint's version of the LG Optimus G shoots 13-megapixel images.
(Credit: Josh Miller/CNET)
In the 808 PureView, Nokia uses a process called "oversampling," which -- for the 808'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 should translate to higher-resolution digital print-outs and zoom-ins than you'd normally see.

It's taken over five years to create the technology within the 808 PureView, Nokia's Alakarhu said. Not only does the 808 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. It's this set of instructions is what Nokia terms PureView, not the sensor size alone.
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.

Key ingredient No. 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 last year's 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 second between shots.
The chip, which lives in the HTC One XOne X+One VOne S, is significant in providing a unified level of photo performance between the four models, whose other features differ quite a bit.
The separate processor also explains how HTC can claim those shot-to-shot times on all four phones in the family.

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.
iPhone 5
The iPhone 5 has fewer controls, but great image processing.
(Credit: CNET)
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.

Usability is king

It's quickly becoming a well-worn adage that the best camera is the one you have on you.
Despite the intense engineering focus that goes into the camera's physical elements, it's hard to overstress the importance of both convenience and the total customer experience. How easy it is to open the camera app from a locked position, how quickly photos capture, and how desired the special effects and shooting modes are all add up to a camera you want to use versus one you don't.

Increasingly, some phone-makers, like HTC and Samsung, include extra logic in their big-ticket phones, like detecting smiles and selecting the best group photo of a bunch.
For most phone owners, said Drew Blackard, Samsung's senior manager of product planning, being able to quickly and easily share photos on the fly is far more important than pixel count. Just look at Twitter and Instagram's runaway success in sharing simple, small photos.
Blackberry Z10, Samsung Galaxy S3, iPhone 5
The Blackberry Z10, Samsung Galaxy S3, and iPhone 5 capture the moment in 8 megapixels.
(Credit: Josh Miller/CNET)
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 online albums, 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 definitely shouldn't scrap pixel count when weighing smartphone camera specs against others, but when it comes to all the hardware and software that create a great photo, the megapixel count alone just isn't enough. It's time we shift the focus somewhere else -- like maybe to that undersung sensor.

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