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.
Photo
Soren
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