THE DIFFERENT TYPES OF DIGITAL IMAGE SENSORS

Two main types of sensors are used in digital cameras today—CCD (charge-coupled device) and CMOS (complementary metal-oxide semiconductor) imagers. Although each type of sensor uses different technology to capture images, these sensors have no apparent quality difference.

Both CCD and CMOS imagers use metal-oxide semiconductors, and they have about the same degree of sensitivity to light.

The main difference is in what each type sensor does with the light after capturing it:

The CCD sensor captures photons as electrical charges in each photosite—a light-sensitive area that represents a pixel. After exposure, the charges are swept off the chip to an amplifier located in one corner of the sensor. External circuitry converts the analog signal to digital form and handles storing it on your memory card.

The CMOS sensor includes solid-state circuitry at each and every photosite and can manipulate the data for each pixel right in the sensor. The CMOS sensor can respond to lighting conditions in ways that a CCD can’t. Every photosite can be accessed individually.

It used to be that the general rule concerning sensors was that the more megapixels a camera had, the better quality of photos from that camera. This is absolutely untrue.

Since the early digital cameras all had the same size sensors and the same size photosites, the quality depended on the number of megapixels the camera had. But as digital technology improved, camera manufacturers developed three different sizes of sensors—small, medium, and large.

The larger an image sensor, the larger the pixels on that sensor. So the overall quality of images with a camera with 16 megapixels won’t be as good as one, also with 16 megapixels, using the largest sensor. That’s because the pixels on the larger sensor are larger. So if a smaller sensor has fewer megapixels, it’s pixels will also be slightly larger. For this reason, many manufacturers reduced the number of megapixels on their smaller sensors but made them slightly larger.

Bigger photosites soak in more light and generate less heat, which means less digital “noise.” Other things being equal, you always want bigger pixels on your sensor.