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Graphics know-how
29
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ELSA GLADIAC
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EN
DirectColor
The situation is different in the case of DirectColor (TrueColor, RealColor and
HighColor). In this case, the value stored in the video memory is not
translated but is passed directly to the D/A converter. This means that the
full color information must be saved for each pixel. The meanings of the
terms RealColor, TrueColor, and HighColor can be confused, as they are not
always used unambiguously.
HighColor and RealColor
HighColor and RealColor usually describe a 15 or 16-bit wide graphics mode,
while TrueColor should only be used for the more professional 24-bit mode
(or 32-bit) mode.
15 bits provide 5 bits each for the red, green and blue values, resulting in 32
levels per RGB component and thus 32,768 (= 32 x 32 x 32) different color
hues.
The 16-bit graphics modes are organized differently. Most common are (R-G-
B) 5-6-5 (e.g. XGA) and 6-6-4 (e.g. i860). 5-6-5 means that 5 bits are used for
each of red and blue and 6 bits are used for green. In the case of 6-6-4, 6 bits
are used for red and green and 4 bits for blue. Both ways of assigning the
bits correspond to the color sensitivity of the human eye: this is highest for
green and lowest for blue. 65,536 different colors can be displayed.
TrueColor
The TrueColor mode is more complex, using 24 bits per pixel. Here, 8 bits are
available for each color component (256 levels), resulting in 16.7 million
different color hues. There are more colors available than pixels on the
screen (1.3 million pixels at a resolution of 1280 x 1024).
VESA DDC (Display Data Channel)
The Display Data Channel provides a serial data channel between the
monitor and the graphics board, as long as both support DDC and the monitor
cable includes the additional DDC wire. An extended monitor cable is used.
This feature allows the monitor data to be sent automatically to the graphics
board (e.g. name, type, max. horizontal frequency, timing definitions etc.) or
even for the graphics board to send instructions to the monitor.
There are various standards; DDC2B and DDC2AB.
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