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How does a digital camera work?

Darrell Young (DigitalDarrell)

Keywords: fundamentals, digital, camera, basics, guides, tips

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How a digital camera operates

The operation of a digital camera, from the standpoint of the user, is virtually the same as the operation of a 35mm camera. Most digital cameras imitate their older film cousins very well, so a new digital user has little to fear in the operation of the camera.


Nikon 2 Megapixel Coolpix 2500 and the 4 Megapixel Coolpix 4500



If you are used to a point-and-shoot, or even an SLR (single lens reflex) 35mm camera, then you will be able to find a digital camera to meet your experience level. If you stay within the same brand of cameras as your current 35mm, you will find that the digital cameras of that manufacturer work about the same as their film cameras.

The biggest difference in the operation of the camera is in the storage medium, and number of images made between changes. For instance, with a 35mm camera, you can have a maximum of about 36 exposures before you have to rewind the film, open the back, and insert another film roll. With digital you might be able to shoot hundreds of images before changing your "digital film". Most digital cameras use a small memory card that inserts into a slot in the camera body. Usually it will be behind a small door on the side or bottom of the camera. The camera manual will explain the process well enough to get started.

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.



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.


Most digital cameras allow you to zoom in or out to change the perspective of the image. Be careful of digital cameras that do not have the word "optical" in the sentence discussing the zoom range.

Nikon 8 Megapixel Coolpix 8700 and the 6 Megapixel D100 DSLR



If your camera only has a digital zoom, it is not really a zoom. An optical zoom actually allows you to change the "field-of-view" of the image, so that you can widen out for a landscape shot, or zoom in for a portrait. It does this by moving lens elements to change the focal length of the camera's lens. Some of the best optical zooms can be as much as 10-to-1 (10x). Most medium priced digital cameras will have a zoom in the 6-to-1 (6x) or 3-to-1 (3x) range. Just BE SURE that you're buying an optical zoom.

In cheaper digital cameras there may be an attractive "digital" (not optical) zoom range mentioned. Usually it will be about 3-to-1 or 4-to-1. The problem with a digital zoom is that it is not a real zoom. The image is simply being magnified and a section of the image taken out of the middle. It is the same thing as if you took a film picture and cropped out everything except a person in the image, then made a big enlargement. You would then only be using a small section of the negative, so grain will increase and sharpness will degrade very quickly. With "digital" zooms, the image is magnified or cropped electronically and the image simply has larger pixels. You are not really zooming in on the subject. Instead, the subject is being electronically magnified, with image degradation as a result. Stay with an optical zoom for best results.

Many cameras come with a combination of optical and digital zooms. That's okay, since the digital zoom is not used until you have maxed out the optical zoom. If you really need that much zoom, though, you might just want to use the old fashioned "sneaker-zoom" whereby you walk toward the subject to make it bigger, or away to make it smaller. Or, you could buy a digital SLR (DSLR) camera and one of those huge long lenses you see at football games.


This varies with the camera manufacturer, so you are only limited by the specific camera you buy. Many cameras allow the use of the very common Compact Flash or CF card. This is a little card about 1/2 the size, and a little thicker, than a business card. It can hold up to hundreds or even thousands of images. Other memory types are Microdrives (MD), Smart Media, Secure Disk (SD), Memory Stick, or even a floppy disk, or CD.

You will need to find out for sure just what type of memory card your camera uses to store pictures. I suggest owning at least two cards. Most will come with an 8 or 16-megabyte "starter card," which will hold only a few pictures unless you set the camera to its lowest resolution. In my opinion, an absolute minimum for today's cameras is a 128-megabyte card. You should really try to get a 256-megabyte card, or even larger if you do more than make an occasional snapshot. The common sizes are: 8, 16, 32, 64, 128, 256, and 512 megabyte. Also, you will find 1, 2, or 4 gigabyte cards and microdrives. The cost for storage cards vary from around $25.00 USD to over $1,000.00 USD.

The really inexpensive digital cameras do not provide an external storage card. They store the pictures in internal memory. Unfortunately, this memory usually won't hold many pictures, so you are very limited. Personally, I would not consider using a digital camera with only internal memory, unless it was all I could afford.

I use a couple of IBM® Microdrives with their one-gigabyte capacity. One of them is equal to eight 128-megabyte cards. The IBM© Microdrive is a tiny hard drive like the big one in your computer, but fits into your camera. Only a few higher-end digital cameras will use the Microdrives though. The bigger the storage -- the greater the cost. Try to get a 128-megabyte or even a 256-megabyte card for your camera, since you will have the freedom to really use your camera with that much storage. If I set my camera to a lower resolution setting using JPEG mode, I can put over 1,200 images on a 1-gigabyte Microdrive.

Compact flash seems to be the most common type of memory card in use these days, so your costs should be a bit less for them due to competition.


As newer and denser sensor chips are developed the megapixel rating of cameras will increase, until eventually we'll have gigapixel, and maybe even terapixel cameras. This is a lot like computers. Remember back when your home computer was rated in mere megabytes. Right now the latest computers are rated in gigabytes, and it won't be long until we have terabyte computers. Digital camera models change like computers. They are doomed to obsolescence as the newer and faster cameras come out. Such is a market society! As this article is being written several 11 to 14 megapixel cameras are on the market.

The more expensive digital cameras offer robust camera construction, "burst mode" shooting that allows you to take a whole bunch of images in quick succession, and an interchangeable series of lenses. Many professional photographers use this DSLR type.

Today, we have basic "consumer" digital cameras that run from $200.00 USD to about $900.00 USD. Then, we enter the arena of the "prosumer" models, which cost from $900.00 USD to about $2,000.00 USD. Finally, there are the "professional" cameras, which start at about $3,500.00 USD and run all the way up to about $8,000.00 USD. So, there is a price range in the digital camera market for about everyone. As more and more people buy and use digital cameras, the cost will decrease. Digital seems to cost about 50% more to buy the camera, compared to film. But, if you shoot a reasonable amount of images, the less costly image processing will help pay for the additional cost of the camera.

In conclusion, buy as many megapixels as you can afford -- two-megapixel minimum. Check to see that it has an optical zoom. Make sure that the buffer will hold at least five or six pictures before transfer to memory card, and get a memory card type that you can afford.

Keep on shooting digital pictures!

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Originally written on July 30, 2003

Last updated on April 29, 2016