Video Graphics Card and Video Systems

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Video Graphics Card and Video Systems

• Mark Joseph Garrovillas
• CE 141 B1

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Outline

• Graphics Card Definition
• Hardware Components and Monitors
• Operating Modes and Memory
• 3D graphics computations

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What's a Graphics Card?

• A modern graphics card is a circuit board with
  memory and a dedicated processor. The processor
  is designed specifically to handle the intense
  computational requirements of displaying
  graphics. Most of these graphics processors have
  special command sets for graphics manipulation
  built right into the chip.
• Graphics cards are known by many names, such as
• Video cards
• Video boards
• Video display boards
• Graphics boards
• Graphics adapter cards
• Video adapter cards

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• Here are the three basic components of a graphics
  card and what they do
• Memory - The first thing that a graphics card
  needs is memory. The memory holds the color of
  each pixel. In the simplest case, since each
  pixel. Since a byte holds 8 bits, you need
  (640/8) 80 bytes to store the pixel colors for
  one line of pixels on the display. You need (480
  X 80) 38,400 bytes of memory to hold all of the
  pixels visible on the display.
• Computer Interface - The second thing a graphics
  card needs is a way for the computer to change
  the graphics card's memory. This is normally done
  by connecting the graphics card to the card bus
  on the motherboard. The computer can send signals
  through the bus to alter the memory.
• Video Interface - The next thing that the
  graphics card needs is a way to generate the
  signals for the monitor. The card must generate
  color signals that drive the cathode ray tube
  (CRT) electron beam, as well as. Let's say that
  the screen is refreshing at 60 frames per second.
  This means that the graphics card scans the
  entire memory array 1 bit at a time and does this
  60 times per second. It sends signals to the
  monitor for each pixel on each line, and then
  sends a horizontal sync pulse it does this
  repeatedly for all 480 lines, and then sends a
  vertical sync pulse.

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Hardware Components
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Graphics Card Interface
CPU sends data through the AGP where it is
received by the video chipset which converts the
data to that appropriate for display. It is
temporarily held in the video RAM so that output
will be continuous. For those with 3D
accelerators, they accelerate the data thus
enabling us to see 3D objects smoothly. For
traditional CRT colored monitors, the output has
to be in analog for the technology of the time ,
these kind of signals allowed more variations
than the digital employed for monochrome displays.
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Use of AGP
AGP has proven itself better than PCI for the
display interface as was reported earlier.
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Monitors
The LCD screen is flat, since it contains no
cathode ray tube (CRT). Instead the screen image
is generated on a flat plastic disk, where
millions of transistors create the pixels.
The digital flat panel monitors are also called
"soft" screens, since their images seems to have
a "softer" quality than those from traditional
CRT monitors. The image does not flicker thus
causing less eye strain.
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A flat panel monitor is digital by nature. There
is no analog electronics included, and that is
the big advantage of this technology. Hence, the
monitor should not be connected through an analog
interface. In fact, using the analog interface,
you get to conversions, which both add noise to
the final image. First the graphics adapter has
to convert the digital data of the PC to analog
electronic signals. Then these analog signals
have to be converted back till digital
information to feed the display. Using the
digital interface, each pixel consists of three
transistors, which each is mapped to the
corresponding memory cell holding the image info.
A purely digital to digital transmission with no
electrical noise involved - that is the way to
produce a stunning image!
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Video Display Modes
Date Standard Description Resolution No. colours
1981 CGA Colour GraphicsAdapter 640x200160x200 None16
1984 EGA Enhanced GraphicsAdapter 640x350 16 from 64
1987 VGA Video GraphicsArray 640x480320x200 16 from 262,144256
1990 XGA Extended Graphics Array 1024x768 16.7 million
  SXGA Super Extended Graphics Array 1280x1024 16.7 million
  UXGA Ultra XGA 1600x1200 16.7 million
Resolution Bit map size with 16 bit colors Necessary RAM on the video card
640 x 480 614,400 bytes 1 MB
800 x 600 960,000 bytes 1.5 MB
1024 x 768 1,572,864 bytes 2 MB
1152 x 864 1,990,656 bytes 2.5 MB
1280 x 1024 2,621,440 bytes 3 MB
1600 x 1200 3,840,000 bytes 4 MB

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When you look at a screen image, it actually
consists of thousands of tiny dots. If you look
close you can spot them Each of these
dots is called a pixel . That is a contraction of
the term Picture Elements. In an ordinary
screen, each pixel consists of three colors Red,
green and blue. Thus, there are actually three
"sub dots" in each pixel. But they are so small
that they "melt" together as one dot The
individual pixel or dot then consists of three
mini dots, also called trio dot . Some screens do
not have round dots, but they work the same way.
With the three basic colors, each of which can be
assigned with varying intensity, you can create
many different colors.
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Video Memory

• The memory that holds the video image is also
  referred to as the frame buffer and is usually
  implemented on the graphics card itself. Early
  systems implemented video memory in standard
  DRAM. However, this requires continual refreshing
  of the data to prevent it from being lost and
  cannot be modified during this refresh process.
  The consequence, particularly at the very fast
  clock speeds demanded by modern graphics cards,
  is that performance is badly degraded.
• An advantage of implementing video memory on the
  graphics board itself is that it can be
  customised for its specific task and, indeed,
  this has resulted in a proliferation of new
  memory technologies
• Video RAM (VRAM) a special type of dual-ported
  DRAM, which can be written to and read from at
  the same time. It also requires far less frequent
  refreshing than ordinary DRAM and consequently
  performs much better
• Windows RAM (WRAM) as used by the hugely
  successful Matrox Millennium card, is also
  dual-ported and can run slightly faster than
  conventional VRAM
• EDO DRAM which provides a higher bandwidth than
  DRAM, can be clocked higher than normal DRAM and
  manages the read/write cycles more efficiently
• SDRAM Similar to EDO RAM except the memory and
  graphics chips run on a common clock used to
  latch data, allowing SDRAM to run faster than
  regular EDO RAM
• SGRAM Same as SDRAM but also supports block
  writes and write-per-bit, which yield better
  performance on graphics chips that support these
  enhanced features
• DRDRAM Direct RDRAM is a totally new,
  general-purpose memory architecture which
  promises a 20-fold performance improvement over
  conventional DRAM.

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Some designs integrate the graphics circuitry
into the motherboard itself and use a portion of
the system's RAM for the frame buffer. This is
called unified memory architecture and is used
for reasons of cost reduction only. Since such
implementations cannot take advantage of
specialised video memory technologies they will
always result in inferior graphics
performance. The information in the video memory
frame buffer is an image of what appears on the
screen, stored as a digital bitmap. But while the
video memory contains digital information its
output medium, the monitor, uses analogue
signals. The analogue signal requires more than
just an on or off signal, as it's used to
determine where, when and with what intensity the
electron guns should be fired as they scan across
and down the front of the monitor. This is where
the RAMDAC comes in.
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The table below summarises the characteristics of
six popular types of memory used in graphics
subsystems
  EDO VRAM WRAM SDRAM SGRAM RDRAM
Max.throughput(MBps) 400 400 960 800 800 600
Dual- orsingle-ported single dual dual single single single
Typical Data Width 64 64 64 64 64 8
Speed (typical) 50-60ns 50-60ns 50-60ns 10-15ns 8-10ns 330MHz clock speed
1998 saw dramatic changes in the graphics memory
market and a pronounced market shift toward
SDRAMs caused by the price collapse of SDRAMs and
resulting price gap with SGRAMs. However, delays
in the introduction of RDRAM, coupled with its
significant cost premium, saw SGRAM - and in
particular DDR SGRAM, which performs I/O
transactions on both rising and falling edges of
the clock cycle - recover its position of
graphics memory of choice during the following
year.
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Memory Calculation

• Lets say you would like to display 256 colors on
  a screen resolution of 640x480. At this
  resolution, there is 307,200 dots, or pixels. 256
  colors requires 8 bits or data for each pixel.
  You can figure this because with an eight digit
  binary, there are 256 possible combinations. For
  two colors, you need only 1 bit, either on or
  off. For 16 colors, you need 4 bits, 2 to the 4th
  power. 256 colors requires 8 bits, and it goes up
  from there. Anyway, multiply the number of dots
  by the number of bits per pixel to get the number
  of bits for the entire screen.
• 307,000 x 8 2,457,600 bits.There are eight
  bits per byte and 1,024 bytes per kilobyte.
  So...2,457,600 / 8 307,200 bytes 300K
• Therefore it requires exactly 300K of memory to
  display 256 colors at 640x480 resolution. But,
  after calculating this, you must consider the
  available amounts. You cannot buy a video card
  with 300K of memory. They were available at
  either 256K or 512K. So, to get this resolution
  and color scheme, you must buy a card with 512K
  of memory on-board.

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Today, a screen resolution of 1024 x 768 defines
the lowest point of high-resolution. That means
that there are 786,432 picture elements, or
pixels, to be painted on the screen. If there are
32 bits of color available, multiplying by 32
shows that 25,165,824 bits have to be dealt with
to make a single image. Moving at a rate of 60
frames per second demands that the computer
handle 1,509,949,440 bits of information every
second just to put the image onto the screen. And
this is completely separate from the work the
computer has to do to decide about the content,
colors, shapes, lighting and everything else
about the image so that the pixels put on the
screen actually show the right image. When you
think about all the processing that has to happen
just to get the image painted, its easy to
understand why graphics display boards are moving
more and more of the graphics processing away
from the computers central processing unit
(CPU). The CPU needs all the help it can get.
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• What Are 3-D Graphics?
• For many of us, games on a computer or advanced
  game system are the most common ways we see 3-D
  graphics. These games, or movies made with
  computer-generated images, have to go through
  three major steps to create and present a
  realistic 3-D scene
• Creating a virtual 3-D world.
• Determining what part of the world will be shown
  on the screen.
• Determining how every pixel on the screen will
  look so that the whole image appears as realistic
  as possible.

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3D Techniques

• Texture mapping is a technique for adding extra
  detail to the 3D object. It is best described as
  wrapping a 2D coloured paper over a 3D object.
  For instance, given a 3D image of a car
  on-screen, a texture would be wrapped over it to
  depict coloured metallic paint. This process is
  painstaking, as it has to be repeated for every
  pixel on the object and each pixel of the texture
  - known as a texel - which lies on top. Many
  textures can be wrapped over the same object, and
  this is multitexturing.
• Mip mapping can be viewed as a cut-down form of
  texture-mapping in which more texels are created
  without performing the equivalent number of
  calculations. If a mip-map is one fourth the size
  of the original texture, reading a single texel
  from this mip-map is the same as reading four
  texels from the original texture. If applied
  using proper filters, the image quality is
  actually higher, as it smoothes out jagged edges.
  
• Bi-linear filtering reads four texels, calculates
  their average - that is, the average of their
  relative positions - colour and so on, and
  displays the result as a single-screen texel.
  This results in blurring at close quarters, which
  in turn reduces an otherwise blocky, pixelated
  appearance. Bi-linear filtering is now standard
  on most PC graphics cards.

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• Z-buffering is a method of calculating pixels
  which have to be loaded into the frame buffer,
  the memory that stores soon-to-be-displayed data.
  3D accelerator chips take one pixel, render it,
  and proceed to the next one. The problem with
  this method is that the accelerator has no way of
  knowing whether the calculated pixel is to be
  displayed immediately or later. Z-buffering
  includes a "Z" value in every calculated pixel.
  If the Z value for a particular pixel is smaller
  than another one, it means the pixel with the
  smaller Z value must be displayed first.
• Anti-aliasing is a technique to reduce the
  "noise" present in an image. To represent any
  image, a certain amount of information is needed.
  If the object is in motion, ideally, that
  information should include its every possible
  position, colour, size changes etc. But if this
  information is not available, the CPU often fills
  in the missing segments with meaningless noise.
  Anti-aliasing, along with mip mapping, removes
  this noise.
• Gouraud shading makes objects appear more solid
  by applying shadows to the surface of the object.
  The algorithm determines the colours of adjacent
  polygons and makes a smooth transition between
  them. This ensures that there is no sudden change
  in colour over the object.
• Bump mapping is an improvement on the more common
  "embossing" technique used to give a "bumpy" look
  to surfaces. It uses three distinct texture maps
  to create the illusion of depth on a surface and
  can be used to create effects such as pockmarked,
  bullet-riddled walls and rough terrain. However,
  the industry is yet to arrive at a standard set
  of procedures to render this visually impressive
  feature.

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Drawn with polygons
Anti aliased texture map
Perspective, lighting, shadows and surfaces added
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3D Transforms

• The first part of the process has several
  important variables
• X 758 -- the height of the "world" we're
  looking at.
• Y 1024 -- the width of the world we're looking
  at
• Z 2 -- the depth (front to back) of the world
  we're looking at
• Sx height of our window into the world
• Sy - width of our window into the world
• Sz a depth variable that determines which
  objects are visible in front of other, hidden
  objects
• D .75 -- the distance between our eye and the
  window in this imaginary world.
• First, we calculate the size of the windows into
  the imaginary world.
•                                                 
                                                    
         
• Now that the window size has been calculated, a
  perspective transform is used to move a step
  closer to projecting the world onto a monitor
  screen. In this next step, we add some more
  variables.
•                                                 
                                                    
                                 
• So, a point (X, Y, Z, 1.0) in the
  three-dimensional imaginary world would have
  transformed position of (X', Y', Z', W'), which
  we get by the following equations
•                                       
• At this point, another transform must be applied
  before the image can be projected onto the
  monitor's screen, but you begin to see the level
  of computation involved -- and this is all for a
  single vector (line) in the image! Imagine the
  calculations in a complex scene with many objects
  and characters, and imagine doing all this 60
  times a second. Arent you glad someone invented
  computers?

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Texture Mapping Example
/ Calculate the step value for the x and y
coordinates. For every pixel on the
destination, the x coordinate on the texture
will move xincr pixels. / xpos tmapx1ltlt8
ypos tmapy1ltlt8 asm .386 push
ds cld mov cx, word ptr length /
Set length / shr cx, 1 les di,
dest / Set destination ptr / lds si,
src / Set source ptr / mov dx, word
ptr ypos / Put the y in the low word /
shl edx, 16 / Move the y to
the high word / mov dx, word ptr xpos /
Put the x in the low word / mov si, word
ptr yincr / Set up the increments the /
shl esi, 16 / same way / mov si, word
ptr xincr / Now to advance one pixel, we
can add edx and esi together to advance the x
and y at the same time, with the fractional
portion automatically carrying at 256. /
cmp cx, 0 je onepixel tlineloop
asm mov ebx, edx shr ebx, 16
/ BH now contains the y coordinate /
mov bl, dh / Store the x value in BL, / /
BX is now an offset into the texture image,
between 0 and 65535. / mov al, dsbx /
Get the color from the texture image /
add edx, esi / Advance one pixel / mov
ebx, edx / Repeat the above, and get another
pixel / shr ebx, 16 mov bl, dh
mov ah, dsbx add edx, esi
stosw / Store a word to the destination /
dec cx / Decrease length / jnz
tlineloop / Repeat for all pixels /
onepixel asm mov cx, word ptr
length and cx, 1 jz tlinedone
mov ebx, edx shr ebx, 16 / BH now
contains the y coordinate / mov bl, dh /
Store the x value in BL, / / BX is now an
offset into the texture image, between 0
and 65535. / mov al, dsbx / Get the
color from the texture image / mov
esdi, al tlinedone asm
pop ds
Our basic texture mapped line routine looks like
this Calculate the x step value Calculate
the y step value Make a coordinate variable
equal to the left endpoint's texture coordinate.
For x x1 to x2 Read a pixel from the
texture Put pixel on screen Add x step
value to the texture coordinate Add y step
value to the texture coordinate End for
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END OF PRESENTATION