The ABCs of camera phone technology
- 11 May, 2012 20:15
Camera phones have come a long way since the first sub-megapixel models of the late 1990s and early 2000s. Aside from being more broadly available -- there's barely a phone sold today that doesn't have a camera -- they've also become much less of a novelty and much more useful as cameras.
Thanks to general advances in camera technology, which benefited both standalone cameras and phones, a good camera phone today takes pictures that are on a par with a previous generation of point-and-shoots. Camera phones now can have double-digit megapixel counts, genuine optical zoom and the ability to shoot true HD video. It's gotten to the point where, according to Flickr's metadata harvesting, the #1 camera overall among Flickr's users is the one on the iPhone 4.
In this article, I look at the key technologies that have allowed camera phones to become good enough to be the default way many users take pictures. But I'll also examine what it is that still sets apart a full-blown camera -- whether it's a pocket-size point-and-shoot or a professional-level DSLR -- from its smaller phone-based brethren.
Image sensors: CMOS vs. CCD
The core technology of any digital camera is the same, regardless of how it's packaged: a lens, an image sensor and image-processing hardware. A camera phone has to cram all of this into a space that's usually about the size of a dime.
A history of camera phones
Is it a camera that also has a phone, or a phone that also has a camera? If you want to know where we've been and where we're going in this area of technology, check out our slideshow:
CCD image sensors, the more mature and established of the two technologies, pipe a signal from each pixel in the sensor to a single (analog) output, which is then processed in separate circuitry. This way, more of the silicon can be used for image capture, as opposed to image processing. The overall image quality is higher, but at the cost of greater power drain. As a result, there have been very few phones that have used CCD; one exception was the Sharp Aquos Shot 933SH, which was never released in the U.S.
With CMOS, a legacy technology recently adapted to imaging, each pixel sensor performs its own light-to-signal conversion and then passes the resulting digital information to other signal-processing circuitry on the same die. Because CMOS packs more functionality into a single chip, it's easier to integrate into other systems -- such as phones -- and requires less energy.
CMOS's big drawback, however, is the "rolling shutter" problem. Because the image sensor acquires its image by scanning line-by-line -- instead of all at once -- anything in extremely fast motion (for instance, a helicopter propeller) will be distorted in bizarre ways. These limitations show up most profoundly when shooting video, but they can mar still images as well. Software can compensate for these problems to some degree, but can't eliminated them entirely.
That said, CMOS is being continuously improved in ways that make it more useful in phones. Consider "back-side illumination," which increases CMOS light sensitivity by placing the sensor-to-sensor wiring in the CMOS behind the sensors rather than in front of them. The iPhone 4 camera uses this technology, and sensors made by Toshiba and Sony now use it as well.
Lenses: Why megapixels alone aren't enough
Anyone who's followed the evolution of conventional digital cameras couldn't help but notice how most of the conversation seems to be dominated by talk of megapixels. Granted, the more pixels in the sensor, the bigger the native resolution of the image. But the quality of the image fed to the sensor depends on another, far more fundamental camera technology: the lens.
Camera phone lenses are constrained by the size of the phone, so phone makers have made up for this in one of two ways: creating better sensors (as described above), and creating more advanced lens technologies.
Most of us are familiar with the basic ground-glass lens, where glass is first cast in a basic structure and then machine-tooled into a more specific shape. These lenses still yield the best quality, despite the cost and the manufacturing effort. A second method, injecting polymer into a metal mold, allows for rapid production but at lower quality. The fixed-focus lenses on low-grade camera phones typically use polymer lenses.
A sample wafer scale lens. The entire package includes a lens and a sensor in a space of only a few millimeters. Image courtesy Alps Electric Co. Ltd.
A third approach, the wafer-scale lens, uses some of the same silicon-wafer manufacturing techniques used for microprocessors. The results are still not quite of the same grade as full-blown glass, but they allow the sensor to be packaged into a much smaller space. They can be found in a few phones such as India's OliveSmart V-S300 and the older Nokia 2330.
Camera phone software
Most camera phones ship with a default picture-snapping app, which traditionally does little more than take very basic photos. As a result, third-party camera apps that let users improve, edit and/or share their images have been developed to fill the void. Most recently famous, thanks to its acquisition by Facebook, is Instagram, a photo-snapping app with some funky filtering and useful sharing options (for both iOS and Android users).
Any photo app is going to be limited by two things: the phone's own hardware, and the way the phone's operating system makes that hardware available to applications. It may be possible to get around some of those limitations by rooting or jailbreaking the phone, but that's not always practical.
Consequently, photo apps can improve picture quality by only so much, so most third-party camera apps instead supply photo-management, image-adjustment and picture-taking features -- in other words, ways to make the process more convenient.
Phone cameras versus standalone cameras
I've hinted before at how phone cameras tend to be more convenient but less functional than their full-blown camera cousins. Here are some of the other major ways standalone cameras and phones diverge.
Flash. Camera phones, when they have a flash at all, tend to have a small LED flash as opposed to a full camera's Xenon-powered flash bulb. This isn't surprising: A large flash would be difficult to integrate with a phone without it being both cumbersome in size and a battery drain.
iPhone users can pick from a number of different flash add-ons. The iFlash iPhone camera flash adds an auxiliary LED flash via the iPhone's docking connector, and FastMac's iV for the iPhone adds a flash and a slew of other accessories via a snap-on shell. There are also third-party, non-phone-specific add-ons such as Phlash, a sidecar LED light that uses its own battery.
Lenses. As mentioned before, phone camera lenses have been a liability for a long time. They've tended to be tiny, cheaply made, limited in their focal length and, with one or two exceptions, lacking optical zoom. These issues are slowly being resolved with each successive generation of phones -- the Nokia N8 had a genuine glass Carl Zeiss f/2.8 lens back in 2010 -- but there are still other limits that are tough to work around.
For example, with a DSLR or even a point-and-shoot, manufacturers can include larger lenses, and so can pipe that much more light -- and that much more image detail -- directly to the sensor. Also, DSLR lenses are interchangeable (but pricier). For most camera phones, the lens you get on the camera is the lens you're stuck with.
iPhone owners do have some alternatives; for example, there are add-on lenses that allow full-blown DSLR camera lenses to be attached to the iPhone (albeit clumsily) and that snap a full 360-degree panorama (in conjunction with special software).
The size of the lens can be as significant as the megapixel rate. This Motorola Cliq XT has a 5-megapixel camera and a very small lens. The element shown here contains both the lens (to the right) and an LED flash. An LG Optimus T with a 3.2-megapixel camera; because of the larger lens, reviews mentioned it did reasonably well in low-light conditions. The lens of the Canon PowerShot SD880 IS point-and-shoot camera. A larger lens admits more light, which allows the camera's 10-megapixel sensor to be put to better use.
Battery. Batteries for standalone cameras can afford to be larger and provide more of the stamina needed to run the camera for long periods of time. With a camera phone, snapping pictures by itself doesn't drain much battery power, but the use of a flash might. Shooting video also eats battery life, although the exact impact will vary among phone models, depending not only on battery capacity but also on the video compression hardware used.
What's more, a standalone camera's battery is designed to be swapped with minimal interruption, since a camera can power back up quickly after a battery change. Changing batteries on a phone is far more onerous (assuming you can change the battery to begin with) and requires the phone to go through a reboot process that can take minutes.
From standby to snap. The current crop of standalone cameras can go from standby to taking a photo in a couple of seconds, since they're not built to do anything but take pictures. Camera phones can take a little longer to be picture-ready, although the biggest delays typically involve navigating the phone's UI to activate the phone app. Some more recent phones, such as those equipped with iOS 5 or Android 4.0, get around this by letting you access the camera directly from the lock screen. However, phones with a dedicated camera button tend to be more on par with their full-blown camera counterparts for speed.
Attachments. Camera phones don't come with a place to insert a tripod mount or a hot shoe (for adding an external flash), two features common to full cameras. On the other hand, there are third-party add-ons for allowing a phone to be mounted on a tripod (the MobiMount, for instance).
Image formats. Camera phones typically shoot JPG and nothing but, with compression levels and image post-processing fixed at the factory. Standalone cameras -- DSLRs in particular -- can shoot images in the uncompressed RAW image format, which are direct copies of whatever comes from the image sensor (and which are usually preferred by serious photographers).
Network connectivity and geotagging. One clear advantage that phone cameras have is network connectivity: Any pictures taken can be automatically uploaded to the service of your choice, with geolocation data automatically embedded in the picture courtesy of the phone's GPS. The Eye-Fi SD card solves some of these problems for standalone cameras. Add the card to a camera, and photos taken from that camera can be automatically uploaded via Wi-Fi to the computer or online service of your choice.
Video. Mobile phones have been able to shoot video for some time, albeit primitively. The first mobile phones able to shoot full HD 1080p video, like Apple's iPhone 4S, are now on the market, which in theory puts them on a par with standalone cameras that can do the same. That said, image quality is still limited by the optics and the video compression in the device.
Separation of functions. Some people just prefer to have their phone and their camera as separate devices. If one is lost or damaged, it can be replaced independently of the other, and each can also be upgraded independently of the other.
The future of camera phones
There's little reason to doubt that camera phones will continue to pack in the megapixels, but be on the lookout for other technological improvements that will matter at least as much, if not more, than sensor sizes.
The Polaroid SC1630 is more of a camera with an Android interface than an Android phone with a camera included.Click to view larger image
First: form and function. Phones such as the Polaroid SC1630 are attempts to create a new form factor and functionality niche. Currently planned to have no cellular access, the SC1630 won't be a true phone at all, but a 16-megapixel device with 3X optical zoom that offers Wi-Fi connectivity and a touchscreen interface that you can load up with Android apps.
The SC1630 is due to ship later in 2012. Future models in the same vein could serve as a replacement not only for point-and-shoot cameras, but for mini- tablet-style devices as well.
We can also look forward to new optical technologies, which will make the limits of the form factor less constraining. Consider liquid lens technology, which uses voltages to change the shapes (and thus the focal behavior) of electrosensitive fluids inside a capsule. According to manufacturer Optilux, liquid lenses also use less power and focus faster than conventional voice-coil focusing technology (the technology used to drive the focusing system for a camera lens). Optilux has plans on the table to introduce the technology into cellphones sometime next year.
Liquid-lens technology uses electrosensitive liquids instead of solid optics. Image courtesy of Optilux.
The technical limitations against pro-level features, like 1080p video or RAW-format imaging (currently available in DSLRs), are also vanishing. What remains to be seen is if there's enough of a market within the camera-phone user base for those functions -- in other words, whether they'll be a selling point for high-end camera phones, or whether pros will just continue to opt for standalone devices.
The future of the camera phone, in short, lies in making it that much more like the cameras we still buy separately -- and to give us that much less of an incentive to buy a separate camera. Pros won't give up their DSLRs anytime soon, but there's a fair chance your next point-and-shoot will be a phone. That is, if it isn't one already.
Check out our slideshow Camera phones: A look back and forward.
Useful photo apps
Third-party camera apps can't magically add megapixels to your phone's image sensor, but they can make the process of snapping and manipulating pictures all the more fun.
Action Snap (free; "Pro" version $3.99) is an Android app that lets you take multiple photos at once across a short timespan, then combine them into a single photo-mosaic.
Camera+ ($0.99) for the iPhone sports many features aimed at improving the process of picture-taking, such as a grid-alignment system to allow shots to be aligned properly, exposure control and automatic image enhancement.
Instagram (free), a cult-favorite photo app for the iPhone and now Android as well, garnered its reputation by being a fast way to snap, manipulate and share pictures. The resulting photos have the vintage, squared-off look of a Polaroid photo -- a fun way to make a digital camera feel analog and retro.
Nightcap ($0.99) allows the iPhone's camera to be used for timed exposures, making for better photography at nighttime and in near-total darkness. Just be sure to hold the camera steady.
Photaf Panorama (free; "Pro" version $3.99) lets you easily shoot multiple images with your Android phone and stitch them together to create a photo panorama. Note that a full 360-degree panorama can take several minutes to stitch together, so you'll do better with a faster phone.
Snapseed ($4.99) is an iOS app that has been touted as an "Instagram-killer," but that's a misnomer -- it's better thought of as a complement to it. It's a photo-tweaking app with some of the same features as Instagram (vintage-look images, etc.), but also has features like area enhancements, a tilt-shift filter for dramatic use of focus, and connectivity to various photo-sharing sites. An Android version is promised.
Serdar Yegulalp has been writing about computers and information technology for over 15 years for a variety of publications.
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