Chapter 20, Additional Exercise 6: Analyzing a Description of a Digital Camera

Evaluate the effectiveness of the following description of a digital camera (based on Farkas, 2000, http://www.cnn.com/2000/TECH/computing/06/15/digital.camera.idg/index.html). Which aspects of the description are successful? Which parts of the description would you change? Why?

A digital camera is a camera that captures images electronically, storing them in memory instead of on film. Digital cameras capture images on a sensor array instead of on film, then store them in flash memory.

Digital and Film Cameras

When you click the button to take a picture—digitally or with old-fashioned film—light passes 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. Digital cameras capture an image with a light-sensitive sensor array instead of film. The most common sensor array is the charge-coupled device (CCD). Essentially a silicon chip about the size of a fingernail, a CCD has light-sensitive diodes arranged in a grid across its face.

Registering an Image

A CCD array can have millions of sensors, each of which 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 (ADC) 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. Almost all newer digital cameras also store files in flash memory cards inserted into the camera. Flash memory is RAM, similar to the RAM used by your computer.

Uploading the Image

Once you have stored the image, you can upload the file to your PC for editing or printing. Most digital cameras come with 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. Some printers let you print directly from a memory card.

Megapixels and Prices

Cameras with 1- or 2-megapixel captures are fine for snapshots and Web images, and cost about $100 from vendors such as Olympus, Epson, and Kodak. Midrange cameras, which cost from $150 to $300, capture approximately 3–4 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.

Cameras in the $300 and up range capture more than 5 megapixels, for images of about 2048 by 1536 pixels—large enough for very high quality 8-by-10-inch prints. Professional-level cameras, with features comparable to those in high-end film cameras, start at less than $1000. Although most new cameras come with flash memory, you can buy additional cards to expand your storage capacity. Flash memory cards come in denominations up to 1 or even 2GB; a 1GB card can cost less than $40.

Editing an Image

After you've saved an image (or several dozen) on your hard drive, you'll want to tweak the image. 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.

Printing an Image

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 start at less than $100. However, they often require special paper—at about 30 cents per sheet—to produce the best results.