8
Therefore bitmap is commonly used to store black-white images. Other definition says
that each pixel may contain more bits to store the information. For example eight bits
per pixel can be used to code 256 tones of grayscale (www.wisegeek.com [referred
25.03.2010]).
Grayscale is a colormap that usually stores information about the image in eight bits
per pixel. Like mentioned before, with eight bits it is possible to create scale of 256
shades of gray. Sometimes grayscale is described as carrying only one pixel which
stores information about brightness of black. Result is a scale of different tones of
gray. All range of gray may be represented as RGB triple value. All three numbers
have to be equal, for example (123,123,123) or (3,3,3).
Another useful colormap is called indexed colormap. Each pixel of image stores in-
formation about index to the place in colors array, for example set by the user. The
biggest palette can contain 256 colors. Indexed color is very useful. It saves comput-
er’s memory and disk space. Smaller color palettes can be used to represent icons and
pictures with small range of colors. Indexed colormap also supports setting transparent
color. Picking transparent pixels is very helpful when it comes to images with irregu-
lar shapes. Thanks to that feature object on image can be put on a background without
necessity of deleting rectangular shape (Vanderburg et al. 1996, chapter 12).
More advanced colormap is called truecolor. Information about the image is stored in
24 bits, which equals 3 bytes. Each color from RGB model gets 8 bits for storage of
information about shade and channel of color. Truecolor system uses at least 256
tones of each color (red, green and blue), which gives huge range of usable colors -
16.777.216 possible variations. This system is often used in high quality photographs
and complex images (Ozimek, lectures from Digital image processing, 2010a).
There are plenty of colormaps but one more worth describing is called highcolor. It
offers very wide range of colors, bigger than in truecolor system. The description of
point on the image contains 16 bits of information. This amount allows to code from 0
to 65535 different values for one RGB color, which gives 65535*65535*65535 color
variations. The precision in highcolor system is twice much better than in truecolor.
Mostly because that highcolor is used while photographing more prevalent colors, for
example skin tones or skies (Ozimek, lectures from Digital image processing, 2010a).