All about graphics
ELSA SYNERGY II
20
VGA
In VGA graphics adapters, the digital color information stored in the video memory (4 bits
for 16 colors or 8 bits for 256 colors) is converted into a digital 18-bit value in the graphics
adapter in a CLUT (ColorLookUpTable). The 3 x 6 bits are converted separately for R/G/
B (red/green/blue) in the RAMDAC (D/A converter) and transferred to the monitor as ana-
log signals on just three lines (plus sync lines). The original color values are converted
into completely different values by means of a translation table. The value stored in the
video memory is thus not a color value, but only a pointer to a table in which the actual
color value is found. The advantage of this method: Only 8 bits need to be stored for each
pixel, although the color values are 18 bits wide; the disadvantage: Only 256 colors can
be displayed simultaneously from a palette of 262,144 possible colors.
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 True-
Color 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 ).
Summary of Contents for Synergy II
Page 1: ...ELSA SYNERGYTM II User Manual...
Page 28: ...All about graphics ELSA SYNERGY II 22...
Page 34: ...Appendix ELSA SYNERGY II 28...
