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How digital cameras work

PC World

June 15, 2000
Web posted at: 2:37 p.m. EDT (1837 GMT)

(IDG) -- Digital cameras: Devices that capture images electronically, storing them in memory instead of on film.

For a few years digital cameras have provided the easiest way to post photos on a Web site or to send photos to friends by e-mail. But digital photos couldn't compare to film when it came to cracking open the photo album to share, in person, memories of your last vacation. Times have changed: New high-resolution digital cameras, coupled with photo-quality printers, mean you can ditch film altogether. And as prices continue to fall, your days of dropping off film for processing could be over.

  • Digital cameras capture images on a sensor array instead of on film and store them in flash memory.

  • Increased resolutions mean you can take high-quality pictures, but doing so will cost you in file size.

  • Prices have dropped to about $300 for cameras that work fine for snapshots and Web images.

When you click the button to take a picture -- digitally or with old-fashioned film -- the camera lets light pass through a lens. In traditional cameras, the light contacts light-sensitive film, changing the film's chemistry and capturing a negative of an image. This image is revealed when the film is developed.

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Digital cameras capture an image with a light-sensitive sensor array instead of film. The most common sensor array is the charge-coupled device. Essentially a silicon chip about the size of a fingernail, a CCD has light-sensitive diodes arranged in a grid across its face.

Capturing the image

A CCD array can have millions of sensors. Each registers the brightness of a color (red, green, or blue) at its position. An array with a million sensors is said to capture a "megapixel" of data.

This brightness data is read, one row at a time, by an analog-to-digital converter that changes the brightness readings (captured by the CCD as differences in voltage) to digital data. By comparing data from adjacent red, green, and blue pixels, the ADC determines and records the color of each pixel.

For example, if red, green, and blue are each at maximum brightness, the pixel is white. If all three are at minimum brightness, it's black. Millions of colors can be described by the differences in the three brightness readings at each pixel. The data is then color-corrected, compressed, and stored in memory.

In a film camera, the film acts as both image capturer and storage medium. Digital cameras store the images as files, just as you store files on your computer.

Older digital cameras and some entry-level cameras save images on memory chips in the camera itself. When the memory is full, you must delete unwanted images or upload the images to a computer to clear the memory. Most newer digital cameras store files in flash memory. Think of flash memory cards as digital film. Flash memory is RAM, similar to the RAM used by your computer, but with an important difference: A computer's RAM loses all stored data when the computer's power is turned off. Flash memory maintains recorded data until it is intentionally erased -- even when the device is removed from a power source.

Once you have stored the image, you can upload the file to your PC for editing or printing. Most digital cameras come with serial or Universal Serial Bus cables and software that lets you upload images to your computer. Alternatively, you can use a flash card reader that lets your computer read a memory card as if it were a removable disk. Some printers let you print directly from flash memory.

A camera for every occasion

Digital cameras used to offer big price tags and low quality. But that trend has reversed: You can now get serious resolution for less than $1000, and the newest cameras capture more than three megapixels of image data. Coupled with new printers and printing services, such cameras can produce copies that look as good as film.

If you want a digital camera, there's one to suit your needs. Entry-level cameras such as KBGear's JamCam capture images at 640 by 480 pixels and start at about $90. The trade-offs: Images aren't of the best quality, and most of these cameras have no removable memory.

Cameras with 1-megapixel captures are fine for snapshots and Web images, and cost about $300 from vendors such as Olympus, Epson, and Kodak. Midrange cameras, which cost from $500 to $900, capture approximately 2 megapixels of data, resulting in image sizes of about 1600 by 1200 pixels. Such cameras let you print a letter-size photo on an ink jet printer, or a high-quality 5-by-7-inch image.

The latest cameras capture more than 3 megapixels, for images of about 2048 by 1536 pixels -- large enough for very high quality 8-by-10-inch prints. They cost about $1000. Professional-level cameras, with features comparable to those in high-end film cameras, start at about $4000.

Extras and add-ons

Although most new cameras come with flash memory, you can buy additional cards to expand your storage capacity. CompactFlash and SmartMedia are the two most popular forms of this memory. CompactFlash cards come in denominations up to 128MB; an 8MB card costs about $40. SmartMedia cards can store up to 64MB, and an 8MB card costs about $30.

After you've saved an image (or several dozen) on your hard drive, you'll want to tweak the image to make it perfect, or to just add some funky effects. Most cameras come with basic image editing software (such as Adobe PhotoDeluxe) that lets you edit and enhance your pictures. If you want more options, you can buy an advanced package such as Adobe's Photoshop or Corel Photo-Paint.

Several companies have special ink jet printers that make photo prints that are as good as or better than those developed from film. Such printers, from companies including Epson, Hewlett-Packard, and Lexmark, print at up to 1440-dot-per-inch resolution and cost between $300 and $900. They often require special paper to produce the best results.

But you don't have to buy a printer. Web sites such as Kodak PhotoNet, Ofoto, and Mystic Color Lab let you upload digital pictures to your own area on the site to share with others or to have them printed and mailed to you.

Digital cameras will keep getting better. Analysts from research group IDC predict that 4-megapixel cameras will be available by next year for about $1000. This will push down the prices of other models to the point where 1-megapixel cameras may start at $200.

The drop in prices and the improving quality make digital cameras an attractive alternative to film for just about everybody. In fact, InfoTrends Research Group expects digital camera sales to outpace film camera sales by 2002. With high-resolution files and the latest printing technology, a digital photo can look as good as what you get from the photo lab. Put all that together, and it may be time to put away the film and go digital.

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