How does a digital camera work?

Photography is undoubtedly one of the most important inven­tions in history -- it has truly transformed how people conceive of the world. Now we can "see" all sorts of things that are actually many miles -- and years -- away from us. Photography lets us capture moments in time and preserve them for years to come.

Digital photography has many advantages over traditional film photography. Digital photos are convenient, allow you to see the results instantly, don't require the costs of film and developing, and are suitable for software editing and uploading to the Internet.

The digital camera is one of ­the most remarkable invention in the field of photography and it is truly different from its predecessors. Conventional cameras depend entirely on chemical and mechanical processes -- you don't even need electricity to operate them. On the other h­and, all digital cameras have a built-in computer, and all of them record images electronically.

In this article, we'll find out exactly what's going on inside these amazing digital-age devices.­

HOW IS THE IMAGE STORED? (or what is a megapixel?)

When you take a picture with a digital camera the light strikes a digital sensor array, instead of a piece of film. These digital sensors are computer "chips" with names like CCD, CMOS, Foveon, or others. They take the place of a piece of film that must be moved across the focal plane of the camera. The digital sensor is made of millions of tiny sensor points called "pixels," which is short for "picture elements." They are laid out in an array with rows and columns, like in a computer spreadsheet or wall calendar. For instance, my camera has an array of sensors in its CCD that is 3008 horizontally, and 2000 pixels vertically (3008x2000). If you do a simple mathematical formula on the pixel array size you will come up with the "Megapixel" rating of the camera. This is the number that most manufacturers use to sell the camera. The simple formula 3008x2000 = 6,016,000 shows that my camera has over six million pixels, or is a "six megapixel" camera.

Think of megapixels as millions of dots of light that are being stored for each picture. The more dots of light there are, the higher the resolution of the image. More pixel dots = bigger pictures. Usually, the more megapixels the better! It takes a lot of megapixels to make prints on photo paper, so it would be best to get a camera with as many megapixels as you can afford.

When the image strikes the sensor, it gets all those megapixels excited. First the image goes through color filters above the individual sensors. The sensor converts the image from light waves into an analog electrical signal. The analog signal is then run through an analog to digital converter (A-D Converter), where it becomes a pure digital signal. Then it is again put through a series of electronic filters that adjust the white balance, color, and aliasing of the image. Next a compression cycle makes the image as small as possible by dumping unnecessary pixels, for more efficient storage. Now the camera has a nice compressed, filtered, digital signal representing your image.

The image is then transferred into a temporary storage area inside the camera called "buffer memory," or simply the "buffer." When the buffer is full, the image is written out to your storage media, such as a memory card. The buffer size in the camera is an important thing. It tells how many images you can take in quick succession. If you have a tiny buffer in your camera, you will have to wait a bit after you take several images.

In fact, the main thing that drives the cost up on digital cameras is the number of megapixels, and the size of the memory buffer. Most cameras have a reasonable amount of both, so you needn't worry. Even if you can only afford a very inexpensive digital camera, you will still have nice images, you just might be limited in their maximum size on photo paper, and will have to wait a bit when taking images quickly. Almost any digital camera is capable of taking pictures for display on the Internet, or for sending across the Internet as email. Images on the Internet are very low resolution -- about 72 to 100 dots per inch -- so any quality digital camera will be capable of making beautiful images for display there.

WHAT ABOUT PRINTING MY DIGITAL IMAGES?

To make a nice 4x6 inch print will require a camera of at least two megapixels. To go up to an 8x10, or 11x14 inches, it is best to have a four to six megapixel camera. Of course, an image processor can make the smaller megapixel cameras do larger prints by stretching the image a bit. This is a process called "interpolation," which simply means adding extra dots of light (pixels) to make the image larger. Image quality degrades a bit when this happens, but is generally acceptable. So a two-megapixel camera could make a print up to 8x10 if needed. A four or six megapixel camera will do an even sharper image, and can make nice images printed all the way up to at least 11x14 inches.

One nice feature that has not yet arrived on film cameras, other than Polaroids, is the freedom to immediately view the image you just took. Since even low-cost digital cameras have small video monitors on the back of the camera, you are able to see if that image is a keeper, or should be deleted. Think of how much money you will save by only printing the images you like, instead of taking a bunch of film images, keeping the best ones, and shoving the rest in a shoebox in the closet. Digital cameras cost more up front, but cost less over the long run to use. You can afford to take many more pictures than you ever could before using a digital camera.