Digital camera; How they work..(PART-II)

A Thousand Points of Light: How Digital Images Are Formed

Digital cameras come in several formats designed for the specialized needs of photographers. They range from inexpensive snapshot models to sophisticated scanner backs that fit on professional large format film cameras. Regardless of their size or sophistication, all digital cameras operate in much the same way.

All images we perceive are formed from optical light energy. Even digital images created within a computer are eventually converted into light energy that we can see. In order for a digital camera to store an optical image, it must be converted into digital information.

A digital camera gathers light energy through a lens, and focuses it on a CCD which converts it into electrical impulses. These signals are fed into a microprocessor where they are sampled and transformed into digital information. This numerical data is then stored, and usually transferred later on to a computer where the image can be viewed and manipulated.

Black-and-White Basics

A black-and-white photograph is composed of a wide range of tonal variations. Like the spectrum of natural light it represents, the photo's tones are continuous and unbroken. By contrast, a black-and-white digital image consists of myriad points of light sampled from the light spectrum. A digital image's range of tone is determined by the camera's capacity to sample and store different light values.

After the CCD converts light into an electrical signal, it is sent to the image digitizer. The digitizer samples areas of light and shadow from across the image, breaking them into points—or pixels. The pixels are next quantized—assigned digital brightness values. For black-and-white, this means placing the pixel on a numerical scale that ranges from pure white to pure black. In color imaging, the process includes scales for color resolution and chromatic intensity.

Spatial Resolution:

Each pixel is assigned an x,y coordinate that corresponds to its place and value in the optical image. The more pixels, the greater the image's range of tone. This quality is called spatial density, and is a vital component of image quality. How good a picture looks is also affected by optical resolution—meaning the camera's optics and electronics. Together, spatial density and optical resolution determine the image's spatial resolution; its tonal spectrum and clarity of detail. In the end, spatial resolution is decided by the camera's lesser most quality: spatial density or optical resolution.

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Bibliography

Books

Baxes, Gregory, Digital Image Processing: Principles & Applications, New York: John Wiley & Sons, Inc., 1994.

Brown, Les, Les Brown's Encyclopedia of Television: Third Edition, Detroit: Gale Research, 1992.

Grotta, Sally Wiener, and Grotta, Daniel, Digital Imaging for Visual Artists, New York: Windcrest/McGraw-Hill, 1994.

Katz, Ephraim, The Film Encyclopedia:Second Edition, New York: Harper Perennial, 1994.

Articles

Baig, Edward C., "Smile—You're on Candid Computer," Business Week, 4 November 1996.

Diehl, Stanford, "Byte's Video Workshop," Byte, May 1995.

Joch, Alan, "Beyond Hollywood," Byte, May 1995.

Lu, Cary, "Digital Cameras on the Move," MacWorld, June 1996.

McNamara, Michael J.,"New Imaging, Today & Tomorrow: 3 New Digital Cameras," Popular Photography, August 1996.

Wiener, Leonard, "Camcorders Go Pro," U.S. News & World Report, 25 November 1996.

Zuckerman, Jim, "Digital Portraits," Petersen's Photographic, September 1996.

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