AntiAliasing

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Anti-Aliasing

• Charles Sampankanpanich

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What is Anti-Aliasing

• anti-aliasing is the technique of minimizing the
  distortion artifacts known as aliasing when
  representing a high-resolution signal at a lower
  resolution
• Anti-aliasing means removing signal components
  that have a higher frequency than is able to be
  properly resolved by the recording (or sampling)
  device. This removal is done before sampling at a
  lower resolution. When sampling is performed
  without removing this part of the signal, it
  causes undesirable artifacts such as the
  black-and-white noise near the top of
• Fools the human eye by making jagged edges appear
  smoother

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How it works

• By altering the colors around the curved or
  diagonal area
• Slight changes such as these make an impression
  that the line is true
• These changes are so small its really hard to
  catch under normal conditions

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ZOMG low frame rates

• There are specific calculations to determine
  which pixels are drawn extra and in what needs to
  be shaded to achieve the desired result to
  represent a diagonal line.
• The graphics card usually does the calculations.
  As a result of these extra calculations, the
  graphics card has to give some of its processing
  power to completing these calculations. This
  affects the amount of processing power left to
  render the scene.
• frame rates are affected by the amount of pixels
  per second your graphics card can render, so long
  as the CPU and other components can keep up with
  it. So when you have anti-aliasing active, the
  amount of pixels that your graphics card can
  render will lower by a degree and therefore cut
  your frame rates in games down.

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FSAA

• Full Screen Anti-Aliasing
• refers to a technique of Anti-Aliasing that
  affects the entire screen not just a certain
  image.
• playing a game with FSAA turned on the graphics
  card will run an Anti-Aliasing algorithm on every
  frame from top to bottom removing jagged edges
  from the entire scene.
• can have a large hit on performance in games and
  has only been overcome recently by having much
  more powerful graphics cards on the market.

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Types of Anti-Aliasing

• Super Sampling and multisampling
• Super Sampling taking the corners of each pixel
  and creating what would be the average color.
  This is then the displayed pixel on the screen.
  Basically you are smudging the image and
  averaging the color along the curve
• This very basic graphic shows you what would
  happen when Supersampling is used in the four
  squares in the centre of this image. 3 of the 4
  squares are in both red and white area's and so
  will be displayed as a shade of orange. One of
  the squares is fully in the white zone and so
  that pixel will be displayed as a pure white
  pixel. If one of the samples was taken from a
  area that was full in the red zone then that
  pixel would be displayed as fully red.

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Types of Anti-Aliasing (cont.)

• Obviously samples are much more complex than
  this, however the principles remain the same. A
  mathematical calculation is done to determine the
  average color for each pixel. Effectively Super
  sampling renders the scene 4 times larger than
  the true scene and is then scaled down once the
  calculations are complete. This is a massive
  performance hit but acheives the best results.
• Multi-Sampling takes multiple samples for each
  pixel.

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Types of Anti-Aliasing (cont.)

• With multisampling each cell on has two samples
  in it. You can see that the other 3 samples are
  taken from neighboring cells. So multisampling
  takes into account the colors around the pixel.
  This is gets you a blend of color to achieve the
  desired result. Multisampling only happens when a
  cell is covered my more than one color, otherwise
  a single colour is chosen and does not need to be
  calculated.

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Pros and Cons

• Pros
• Smoothes out screen fonts
• Rounded edges look to have smooth curves
• Typing can be easier to read due to better
  quality fonts
• Games look prettier and more realistic
• Cons
• Small text can be too blurred to read
• already sharp edges can be made fuzzier
• You cant print out Anti-Aliased text as it blurs
  
• Static image sizes are larger
• Games are affected by lower frame rates