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 quality 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.
Phone manufacturers can opt for one of two major image sensor technologies: charge-coupled devices (CCDs) and complementary metal oxide semiconductors (CMOS).
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.
Tags : camera phones, quality digital camera, ip security camera,wireless ip cameras,mini camera numerique,
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