ELSA Synergy 2000, Руководство пользователя

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Graphics know-how
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| ELSA Synergy 2000 |
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mapping. The some 330 routines of the OpenGL API provide software devel-
opers access to these graphics capabilities:
For further information see the Internet site www.sgi.com/software/opengl .
4.2.4 Color palettes, TrueColor and gray scales
Common graphics modes are listed in the following table. Not all graphics
modes are available on the ELSA boards:
4.2.5 VGA
In VGA graphics boards, the digital color information stored in the video mem-
ory (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 analog signals on just three lines
(plus sync lines). The original color values are converted into completely dif-
ferent 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 dis-
advantage: Only 256 colors can be displayed simultaneously from a palette
of 262,144 possible colors.
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 16 5+6+5 65,536 32
TrueColor 24
32 8+8+8
8+8+8 16.7 million
16.7 million 256
256
(bpp = bits per pixel; bpg = bits per gun)