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Raster, or bitmap, graphics that are manipulated by computers
are rcreated with collections of by dots. If you magnify
almost any computer generated image you will see this pattern
of dots. Each dot may vary in size and color.
These bitmaps can
be defined using three properties: size, resolution and bit
depth.
Size: The
physical height and width of any given image. This can
be measured in inches, centimeters, points, picas or anything
else that you may wish. This size is not to be confused
with the computer file size, which is measured in Kilo-Bytes
(K) or Mega-Bytes (Mg).
Resolution:
This is the simgle most important factor in any computerized
photo. The resolution is the number of dots that fit
into the chosen linear measurement. These dots are called
picture elements or pixels. Since the standard measurement
in the US is inches, this is usually refered to as DPI, or
Dots Per Inch.
If your monitor display is set to 800x600 pixels, and your
monitor's size dimensions are 10.5 by 8 inches then your monitor
displays 75 pixels per inch, or in other words is 75 dpi.
If you change your video settings to 1024 by 768 pixels the
resolution will be 96 dpi. The higher resolution is
due to squeezing more dots into the same space.
A fax machine uses up to 200 dpi. whereas a standard magazine
uses 300 dpi. for its photos.
Bit depth:
The value of pixel specifies its color, the number of bits
required to store the value of the dot or pixel is called
the bit depth. If a picture is color or grey or black
and white the picture usually has a different bit depth.
Black and white images have a very low bit therefore they
can only display two colors, black & white. Greyscale
images can usually display up to 256 different shades of grey
and have a slightly higher bit depth. Color images have
the highest, covering the entire spectrum.
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