Probably (no, definitely) the greatest difference between film and digital photography is the image-storing sensors. In film photography, photos are recorded on tiny particles of grain imbedded in the film emulsion. In digital photography, images are stored in the form of tiny pixels (picture elements) on a magnetic sensor, or memory card. The sensor might be any one of a number of devices, depending on the camera manufacturer. Memory cards go by such names as CompactFlash Card, SmartMedia Card and Memory Stick. Some digital cameras use a small compact disk (CD) as a storage device. In the past, standard 3-1/2 inch floppy disks were used in digital cameras, but these were limited to much fewer images than the other storage devices.
Digital cameras are usually rated by the number of pixels they use to make the highest quality single image. The camera's rating is given in megapixels (1 megapixel is 1 million pixels). Today, the most basic compact digital cameras range from 1 to 4 megapixel. These cameras are good for snapshots and for pictures that will be viewed only on the computer, or e-mailed to friends and relatives. Depending on the camera, they might be okay for prints up to 5 X 7.
More advanced compact digital cameras range from about 4 to 8 or more megapixels. All of these cameras can make excellent 5 X 7 and 8 X 10 enlargements, and many of them can produce 11 X 14 inch photos that rival those made from film.
Pro-type SLR digital cameras range from about 5 to 16 or more megapixels. These cameras provide better quality images than do the compacts because of better image-sending devices, but only a professionally trained person could tell the difference. Along with a higher price tag, SLR digital cameras provide more options than compacts, with some of these being very desirable, and some designed for only the professional photographer.
Unlike film cameras, most digitals offer a range of quality settings. JPEG is the most commonly used setting for digital images. Pictures taken in the JPEG format occupy the least amount of room on a memory card so you could store many images. When a picture is taken in the JPEG mode, it's compressed by having pixels proportionally removed from the image. Most digital cameras provide a range of JPEG settings so you can select the amount of compression you're willing to accept. The highest setting will give the least amount of loss, and could produce an image almost equivalent to that obtained from a completely uncompressed image file.
But degree of compression is relative. For example, if you were to select the middle JPEG setting on a 2 megapixel camera, you'd get a pretty good 4 X 5 print. With a 5 megapixel camera, the middle setting would still be good enough to get a high quality 5 X 7 or a pretty decent 8 X 10.
With all digital cameras, the lowest JPEG setting will result in the greatest amount of compression. This setting is appropriate, and really the most desirable, if you'll only be viewing the images on a computer screen, or sending them by e-mail over the Internet.
Let's take a look at some numbers that you might find on a typical 5 megapixel compact digital camera with a 128 megabyte memory card. When the camera is set for the highest degree of image quality, the image card could hold a maximum of 44 images. At the lowest image quality, it could hold more than a thousand images. Between these extremes, various settings would provide a variety of maximums, depending on the degree of image quality you were willing to accept. For pictures that you wanted to print and display on a wall, you would always want images of the highest quality. For snapshot and e-mailing pictures, the lowest quality would be okay. As a general rule, always shoot at the highest quality in anticipation of wanting the best quality photos, then you can downgrade them, if necessary, on the computer.
Okay, so what if you do take a picture at the greatest JPEG compression ratio, and later decide to display the image on the wall as an 8 X 10 print? Good question. You'll have the image, but it could have been a much better photo if it had been taken at a noncompressed JPEG setting. You could still display it, but probably at the most as a 5 X 7 rather than as an 8 X 10 print.