Digital CameraIn the past twenty years, most of the major technological breakthroughs in c

Digital Camera

In the past twenty years, most of the major technological breakthroughs in consumer electronics have really been part of one larger breakthrough. Whet, you get down to it, CDs, DVDs, HDTV, MP3s and DVRs are all built around the same basic process: convening conventional similar information(represented by a fluctuating wave) into digital information (represented by ones and zeros, or bits). This fundamental shift in technology totally changed how we handle visual and audio information—it completely redefined what is possible.

The digital camera is one of the most remarkable instances of this shift because it is so truly different from its ancestor. Conventional cameras depend entirely on chemical and mechanical processes, you don't even need electricity to operate them. On the other hand, all digital cameras have a built-in computer, and all of them record images electronically.

The new approach has been enormously successful. Since film still provides better picture quality, digital cameras have not completely replaced conventional cameras. But, as digital imaging technology has improved, digital cameras have rapidly become more popular.

Understanding the Basics

To get a digital image, you need the image to be represented in the language that computers recognize—bits and bytes. Essentially, a digital image is just a long string of 1s and 0s that represent all the tiny colored dots—or pixels(像素)—that collectively make up the image.

If you want to get a picture into this form, you have two options:

You can take a photograph using a conventional film camera, process the film chemically, print it onto photographic paper and then use a digital scanner to sample the print(record the pattern of light as a series of pixel values).

At its most basic level, this is all there is to a digital camera. Just like a conventional camera, it has a series of lenses that focus light to create an image of a scene. But instead of focusing this light onto a piece of film, it focuses it onto a semiconductor device that records light electronically. A computer then breaks this electronic information down into digital data.

A Filmless Camera

Instead of film, a digital camera bas a sensor that converts light into electrical charges. The image sensor employed by most digital cameras is a charge coupled device(CCD). Some cameras use complementary metal oxide semiconductor(CMOS) technology instead. Both CCD and CMOS image sensors convert light into electrons. A simplified way to think about these sensors is to think of a 2-D array of thousands or millions of tiny solar cells.

Once the sensor converts the light into electrons, it reads the value(accumulated charge) of each cell in the image. This is where the differences between the two main sensor types kick in:

A CCD transports the charge across the chip and reads it at one corner of the array. An analog-to-digital converter(ADC) then turns each pixel's value into a digital value by measuring the amount of charge at each photosite and converting that measurement to binary(二进制) form.

CMOS devices use several transistors at each pixel to enlarge and move the charge using more traditional wires. The CMOS signal is digital, so it needs no ADC.

Capturing Color

Unfortunately, each photosite is colorblind. It only keeps track of the total intensity of the light that strikes its surface. In order to get a full color image, most sensors use filtering to look at the light in its three primary colors. Once the camera records all three colors, it combines them to create the full spectrum(光谱).

There are several ways of recording the three colors in a digital camera. The highest quality cameras use three separate sensors, each with a different filter. Another meth

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