Page 66 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes The number of entries (logical colours) in the palette is the total number of colours which can
appear on screen simultaneously. The width of each entry determines the number of colours
which the palette can be set to produce.
A common example would be a palette of 256 colours (i.e. addressed by eight-bit pixel values)
where each colour can be chosen from a total of 16.7 million colours (i.e. eight bits output
for each of red, green and blue). Changes to the palette affect the whole screen at once and
can be used to produce special effects which would be much slower to produce by updating
pixels.
The following are some of the widely used meanings for colour palette in computing:
• The total number of colours that a given system is able to generate or manage (though, due
to video memory limitations, it may not be able to display them all simultaneously):
 Full palette: For example, high colour displays are said to have a 16-bit RGB
palette.
• The limited selection of colours that can be displayed simultaneously:
 On the whole screen:

 Fixed palette selection: A given display adapter can offer a fixed colour selection
when its hardware registers are appropriately set. For example, the Colour Graphics
Adapter (CGA), is one of the standard graphics mode, can be set to show the so-
called palette #1 or the palette #2: two combinations of three fixed colours and one
user-defined background colour each.
 Selected colours or picked colours: In this case, the colour selection, generally from a
wider explicitly available full palette, is always chosen by software, both by the user
or by a program. For example, the standard VGA display adapter is said to provide
a palette of 256 simultaneous colours from a total of 262,144 different colours.
 Default palette or system palette: The given selected colours have been officially
standardized by some body or corporation. For example, the well known Web-safe
colours for use with Internet browsers, or the Microsoft Windows default palette.

 On an individual image:
 Colour map or colour table: The limited colour selection is stored inside the given
indexed colour image file. For example, GIF
 Image palette or image colours: The limited colour selection is assumed to be the full
list of the colours the given digital image has, even when the image file does not
employ indexed colour pixel encoding.
• The underlying hardware that may be used to hold those simultaneous colours:

Hardware palette or Colour Look-Up Table (CLUT): In order to show them, the selected
colours’ values must be loaded in the colour hardware registers of the display subsystem.
For example, the hardware registers of the Commodore Amiga are known both as their
colour palette and their CLUT, depending on sources.

4.6.1 Colour palette Generator
A colour generator or colour scheme selector is a tool for anyone in need of a colour scheme. In
most cases these online tools are code driven and full of features to help someone build the perfect
colour scheme. There is somewhere around 50 online generators available for you to use.

60 LoveLy professionaL University