Digital Photography

Capturing the Image

Digital cameras provide a way to digitize real objects. Instead of taking photos with a conventional camera that requies a developing step to visualize the image, a digital camera takes the photo in digital format that can be transfered to a computer.

When you take a photo the image that enters the lens in the form of photons. The camera uses an image sensor to divide the photons into an array of photosites or pixels. There are two types of image sensors that digital cameras use, CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor). These sensors can be thought of as and array of a milliion tiny solar cells.The image sensor whether it is CCD or CMOS ,converts photons into electrical charges. The charge is then read in each photosite of the array.

A CCD transports the charge across the chip and reads it at one corner of the array. An ADC (analog-to-digital) converter turns each pixel's value into a digital value.A CMOS devices use several transistors at each photosite to amplify and move the charge using more traditional wires. The CMOS signal is digital, so it does not need an ADC converter.

Which is better?

  • CMOS sensors are less expensive to manufacture than CCD sensors. CCD sensors require a special process to ensure a high precision of reproduction. CMOS sensors can be manufactured using the same processes used in the manufacture of microprocessors.
  • CMOS sensors require several transistors around each pixel, so photons hit transistors instead of the photosites which affects the quality of the image.
  • CMOS sensors are likely to be found in cheaper cameras producing lower resolution
  • CCD sensors consume almost 100 times the power of an equivalent CMOS sensors, reducing battery life.
  • CMOS might be faster than in CCD. The electrical charge in CMOS as stated earlier is converted from analog to digital at each photosite. The electrical charge in CCD photosites on the otherhand are transported accross the sensor and read as a group.
CMOS Sensor
CCD Sensor
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