From Your Eyes to the Camera's Memory

A traditional camera creates an image by allowing light to pass through a lens onto film. The film is coated with light-sensitive chemicals, and wherever light hits the coating, a chemical reaction takes place, recording a latent image. During the film development stage, more chemicals transform the latent image into a printed photograph.

Figure 2-1: Imaging sensors do the work of film
in digital cameras.

Digital cameras also use light to create images, but instead of film, digital cameras capture pictures using an imaging array or sensor, both of which are fancy ways of saying "light-sensitive computer chips." Currently, these chips come in two flavors: CCD, which stands for charge-coupled device, and CMOS, which is short for complementary metal-oxide semiconductor. (No, Billy, that information won't be on the test.) Figure 2-1 gives you a look at some sensors from Kodak.



Although CCD and CMOS chips differ in some important ways, which you can read about in Chapter 3, both chips do essentially the same thing. When struck by light, they emit an electrical charge, which is analyzed and translated into digital image data by a processor inside the camera. The more light, the stronger the charge.

After the electrical impulses are converted to image data, the data is saved to the camera's memory, which may come in the form of an in-camera chip or a removable memory card or disk. To access the images that your camera records, you just transfer them from the camera memory to your computer. With some cameras, you can transfer pictures directly to a television monitor or printer, enabling you to view and print your photographs without ever turning on your computer.

Keep in mind that what you've just read is only a basic explanation of how digital cameras record images. I could write an entire chapter on CCD designs, for example, but you would only wind up with a big headache. Besides, the only time you need to think about this stuff is when deciding which camera to buy. To that end, Chapters 3, 4, and 8 explain the important aspects of imaging chips, memory, and image transfer so that you can make a sensible purchase decision.