Signal encryption
This optional circuit encrypts the signal for content protection using HDCP or a
competing protocol.
The screen image can be represented in the framebuffer in one of two ways:
??? The RGB information for each pixel can be stored in successive memory locations.
On modern video cards, 8 bits (1 byte) of informaton is stored for each
RGB channel, resulting in a total of 24 bits (3 bytes) of memory used for each
pixel. This permits 224 = 16 million colors to be used simultaneously on the display.
It is also fairly common to use 8, 15, or 16 bits per pixel, and less common
(on specialized cinema-oriented hardware) to use 12 or 16 bits per RGB channel
for a total of 36 to 48 bits per pixel.
Figure 1-3. The components of a video card
Signal encryption
Memory
Framebuffer
GPU
Monitor
Bus interface
Video controller
(CRTC)
Computer bus (PCI-e, AGP, or PCI)
1.11
1.11 Displays, Screens, and Xinerama 19
??? A color code for each pixel can be stored. This results in a ???paint-by-number???
scheme, where the video controller looks up each color code in a palette or
lookup table to determine the RGB value. For example, the color code 3, when
stored in the memory location for a given pixel, would instruct the video controller
to look up entry number 3 in the palette and use whatever color is stored
there.
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