Rather than the smooth gradient of color intensities recorded by film, digital images use numbers to measure light intensities. Because we don't have unlimited numbers, each number represents a range of light intensity. For more detail on digital technologies, see Wikipedia's digital web page.
How are Digital Images Made?
Electronic sensors detect photons of light and create a voltage that represents the intensity of light hitting the sensor. Although our eyes aren't electronic, they act similarly – rather than voltage, the light sensors in the eye create chemicals that tell the brain how much light is being seen. See an animation on the basics of light detection for more detail, read about the basics of digital cameras, or see the digital camera information at HowStuffWorks.com.
A digital picture is made of three fields of color intensity
measurements, and a pixel is the mixture of red, green, and
blue intensities at a location in the picture.
Who Are You More Alike? Use digital photographs to measure faces to see who you look more alike.
Measuring Old Growth Forest Loss—Use digital maps to see how much old growth forest was lost in your area over the past three centuries.
What Has Been in Your Backyard?—Use digital maps of plant populations over time to see what was in your backyard thousands of year ago.
Near Infrared and You—Use special digital cameras to see why some clothes heat up more than others of the same color when exposed to sunlight.