Digital Cameras beginner guide
Digital Cameras - A beginner's guide
by Bob Atkins
Digital Camera Basics - A primer
Digital cameras are confusing to a lot of new users. In this basic guide to digital camera technology
we hope to try to give digital beginners at least some basis to use in deciding which digital camera is appropriate for them. When shopping for a digital camera it's at least good to know what the basic terms like white balance, pixel
mean and how they affect image and print quality. It's also important to know the difference between things like optical zoom
and digital zoom
as well as the advantages and disadvantages between storage
formats such as Compact Flash
, Sony Memory Stick
, Secure Digital
and camera interface technologies
such as USB 1.1
, USB 2.0
and Firewire IEEE 1394.
A pixel is a contraction if the term PI
ement. Digital images are made up of small squares, just like a tile mosaic on your kitchen or bathroom wall. Though a digital photograph looks smooth and continuous just like a regular photograph, it's actually composed of millions of tiny squares as shown below.
Each pixel in the image has a numerical value of between 0 and 255 and is made up of three color channels. So for example a pixel could be 37-red, 76-green and 125-blue and it would then look like this . If it was 162-red, 27-green and 12-blue, it would look like this . There are over 16 million possible combinations using this scheme and each one represents a different color. Computer savvy readers will note that each color in this scheme can be represented by an 8-bit number (byte), so the color of each pixel is defined by three color bytes. This scheme can be expanded, for example to use 16-bits (two 8-bit bytes) for each color. images using three 8-bit values are sometimes called 24-bit color images
. images using three 12-bit values for color definition are called 36-bit color images
, and those using three 16-bit values are called 48-bit color images
One of the main ways that manufacturers categorize their digital cameras is in terms of pixel count
. What this is is the number of individual pixels that go into making each image. Today this number varies between 1 million (1 Megapixel
) to around 14 million (14 Megapixels
). A million pixels is abbreviated to MP, so a 1MP camera has 1 million pixels and a 3MP camera has 3 million pixels. Currently most popular consumer digital cameras have between 2MP and 5MP. A 3MP camera can make excellent 4"x6" prints and very good 5"x7" prints. If you intend to make lots of 8"x10" prints, then perhaps a 4MP or 5MP camera would be a better choice. Sometimes two numbers are given, total pixels and effective pixels. Total pixels count every pixel on the sensor surface. Usually the very edge pixels aren't used in the final image. Effective pixels are the number of pixels actually used in the image after the edge pixels have been dropped.
The aspect ratio of a camera is the ratio of the length of the sides of the images. For example, a traditional 35mm film frame is approximately 36mm wide and 24mm HIGH. This has an aspect ratio of 36:24, which can equally well be expressed as 3:2. Some digicams use the same aspect ratio for their digital images. For example most digital SLR (single lens reflex) cameras have a 3:2 aspect ratio. However, video monitors typically use a 4:3 aspect ratio. For example a monitor with a 800x600 display has a 4:3 aspect ratio. With this in mind, most consumer level digicams use a 4:3 aspect ratio for their images.
The size of the digital sensor element (which is equivalent to the size of the negative for film cameras) is pretty small in all consumer digicams - typically around the size of a fingernail (and a small fingernail at that!). As I said above, a 35mm film frame is 24mm high by 36mm wide but most digital cameras use sensors very much smaller than this. Here are some typical digicam sensor sizes. The "name" of the sensor is based on specification for old TV tubes used in the 1950s. Nobody is quite sure why it's being used for modern digital sensors since the "sizes" don't really relate in any consistent way to the actual physical size of the sensor. However these names are widely used, so it's best to know what they are. They are often listed in digital camera spec sheets.
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