Tutorial
Raster Graphics

1. bandwidth = 3 byte/pixel * 1024x1024 pixels/frame * 60 frames/s = 180 Mbytes/s
   

   If memory is assumed to consist of 32-bit words (every read fetches 4 bytes from memory), then we need to read 45 Mwords/s, or one read every 20ns. Access times for dynamic memories (DRAMs) are typically 70ns, thus framebuffer memory requires special design. See p. 856-861 in the text for details.

2. If the method of calculating pixel values (i.e., the rendering algorithm) produced pixel values at the same rate as the video beam, a framebuffer would not be required. An architecture of this type has been proposed, which uses image-compression techniques to store framebuffer contents in a 'small' memory, and then performs decompression just-in-time. This is not a common graphics architecture -- most graphics architectures store the full contents of the screen in the framebuffer memory.
   
   

3. Pseudocode description:

   // setup the scene in the framebuffer
   reserve colour 0 for the background: white
   for each frame n of animation
     draw ball in colour n
   
   // ok, now let's animate
   // note that no pixels are drawn -- only colour map entries are changed
   set all colours in colour map to white
   for each frame n
     set colour map entry n to blue   // make frame n visible
     display
     set colour map entry n back to white
   

4. 648x486x30x3 = 28 343 520 bytes/s
                = 27.03 Mbytes/s
    1024 Mb / 27.03 Mbytes/s = 37.9 s
   

5. LCD displays
   

   A layer of liquid crystal is placed between two polarizing filters which are 90 degrees out of phase. Applying an electric field to the liquid crystal changes the polarizing effect of the liquid crystal. The electric field can thus be used to block or allow passage of light through the filters + liquid crystal.

   active matrix displays
   

   These are a specific type of LCD display, having a transistor located at each pixel. The transitor allows the state of the liquid crystal to be changed more quickly. It also acts as a memory element, thus allowing a pixel to be 'on' for longer before requiring a refresh, which makes for brighter displays. See text p. 161, 162
   
   

6. In CRTs, how does one prevent the red electron gun from emitting electrons which strike the blue or green phosphors?

   The shadow mask is a thin metal plate perforated with many holes. The red electron beam, holes, and red phospors are all aligned, allowing only elecrons coming from the red electron gun to strike the red phosphor. The same applies to the other colours. See text, p. 159.