ELSA Erazor II - Manual (Page 24)

All about graphics
ELSA ERAZOR II and ELSA VICTORY Erazor LT
18
Color Palettes, TrueColor and Gray Scales
Common graphics modes are listed in the following table. Not all graphics modes are
available on the ELSA ERAZOR II and ELSA VICTORY Erazor LT boards.
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.
Graphics mode bpp bpg
Colors
(from palette) Max. gray levels
VGA 0x12
VGA 0x13 4
8 6+6+6
6+6+6 16 of 262,144
256 of 262,144
16
64
Standard 8
8 6+6+6
6+6+6 256 of 262,144
256 of 16.7 million
64
256
HighColor 15
16
16 5+5+5
6+6+4
5+6+5 32,768
65,536
65,536 32
16
32
TrueColor 24 8+8+8 16.7 million 256
(bpp = bits per pixel; bpg = bits per gun)