Even though digital photography is a revolutionary new way to take pictures, it is very much based on traditional photography and uses many of the same principals. Both types of photography require a lens to focus the light and a shutter to allow the light to enter the camera. The main difference between digital and traditional photography is how the image is captured.
Traditional photography uses film which must be developed in a darkroom using various chemicals. The developing process produces ‘negatives’ which must be printed before you can see the picture. Digital photography uses an electronic sensor to capture the image. The sensor is made up of millions of individual ‘pixels’ (picture elements) which convert light into a number. Rather than waiting for the picture to be developed, digital pictures can be seen almost instantaneously on the viewfinder of the digital camera.
The quality of a digital photograph depends a lot on how many pixels it has. The number of pixels is sometimes referred to as the ‘resolution’ of an image, and can be expressed as a dimension (800 x 600), or the number of pixels per inch. A common resolution for computer screens is 800 x 600 and this means the monitor can display 800 pixels from side to side and 600 pixels from top to bottom for a total of 480,000. Digital photography commonly uses much higher resolutions than computer screens with resolutions in the millions of pixels (megapixels). A camera with a resolution of 2048 x 1536 has a total resolution of 3.1 megapixels.
As mentioned above, each pixel is represented by a number. The size of that number determines the colours scale that can be represented. For example, black-and-white pictures can be represented with pixels which are just eight bits in length. If you are familiar with binary arithmetic, you know that an 8-bit number can represent decimal numbers from 0 to 256. Black-and-white photographs, therefore, can have a total of 255 shades of gray as well as black (0) and white (256).
Colour must be represented with larger numbers. 16 bits per pixel, for example, is necessary to have a colour scale of 65,536 different shades. 24 bits per pixel can represent more than 16 million different colours. Most digital cameras use 24 bits per pixel, but some professional equipment has a colour resolution of up to 48 bits per pixel for more than 280 billion different shades.
There are several factors that affect the quality of a digital camera, but pixel resolution is usually seen as the most important. Choosing an adequate pixel resolution depends a lot on the size of the photographs you want to print. Keep in mind that the number of pixels in an image does not change, so pictures with larger dimensions will have fewer pixels per inch which results in a loss of detail if the picture size becomes too big.
Photo labs usually print pictures at 300 pixels per inch, so using this as a standard measurement you can calculate how many megapixels your camera should have. The maximum print from a two megapixel camera at 300 pixels per inch is 5.8″ x 3.8″ — less than the standard 4″ x 6″. A camera with four megapixels can print pictures to a maximum size of 8.2″ x 5.4″ at 300 pixels per inch.
Of course, there is nothing to stop you from printing larger pictures. Pictures printed at 200 pixels per inch are slightly less sharp but still quite acceptable for many purposes. At this resolution, you can get pictures up to 8.7″ x 5.8″ from a two megapixel camera, and 12.2″ x 8.2″ from a four megapixel camera.
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