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  3. Digital Camera In the past twenty years, most of the major technological breakthroughs in consumer electronics have really b

Digital Camera In the past twenty years, most of the major technological breakthroughs in consumer electronics have really b

admin2009-04-23  42
问题                                       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 method is to rotate a series of red, blue and green filters in front of a single sensor. The sensor records three separate images in rapid succession.
    Both of these methods work well for professional studio cameras, but they’re not necessarily practical for casual snapshots. Next, we’ll look at filtering methods that are more suited to small, efficient cameras. This process of looking at the other pixels in the neighborhood of a sensor and making an educated guess is called interpolation(插补). This method also provides information on all three colors at each pixel location.
    Exposure and Focus
    Just as with film, a digital camera has to control the amount of light that reaches the sensor. The two components it uses(to do this, the aperture(孔径) and shutter speed, are also present on conventional cameras.
    These two aspects work together to capture the amount of light needed to make a good image. In photographic terms, they set the exposure of the sensor.
    Storage
    Digital cameras use a number of storage systems. These are like reusable, digital film, and they use a card reader to transfer the data to a computer. Many involve fixed or removable flash memory. Digital camera manufacturers often develop their own flash memory devices, including SmartMedia cards, CompactFlash cards and Memory Sticks. Some other removable storage devices include: Floppy disks, Hard disks, or microdrives, writeable CDs and DVDs.
    No matter what type of storage they use, all digital cameras need lots of room for pictures. They usually store images in one of two formats-TIFF, which is uncompressed, and JPEG, which is compressed. Most cameras use the JPEG file format for storing pictures, and they sometimes offer quality settings(such as medium or high).
    To make the most of their storage space, almost all digital cameras use some sort of data compression to make the files smaller. Two features of digital images make compression possible. One is repetition. The other is irrelevancy.
    Imagine that throughout a given photo, certain patterns develop in the colors. For example, if a blue sky takes up 30 percent of the photograph, you can be certain that some shades of blue are going to be repeated over and over again. When compression routines take advantage of patterns that repeat, there is no loss of information and the image can be reconstructed exactly as it was recorded. Unfortunately, this doesn’t reduce files any more than 50 percent, and. sometimes it doesn’t even come close to that level.
    Irrelevancy is a trickier issue. A digital camera records more information than the human eye can easily detect. Some compression routines take advantage of this fact to throw away some of the more meaningless data. This way the data can be reduced greatly, sometimes less than one third.
选项 A、Y
B、N
C、NG
答案A
解析 从文章的大小标题就能判断出文章结构及各部分大意，由此可知本文是关于数码相机的工作原理和操作方法的。
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