I
f you draw a diagonal line
with square pixels, their
hard edges create a jagged
‘staircase’ effect. This
ugliness (among other
artefacts) is called aliasing. If
resolutions were much higher,
it wouldn’t be a problem, but
until display technology advances,
we have to compensate with
anti-aliasing.
There are many techniques for
anti-aliasing, but supersampling (SSAA)
is useful to explain the process. It works
by rendering frames at a higher
resolution than the display resolution,
then squeezing them back down to size.
On the previous page, you can see the
anti-aliasing effect of downsampling
SoM from 5120x2880 to 1440p.
Consider a pixel on a tile roof. It’s
orange, and next to it is a pixel
representing a cloudy sky, which is light
and blueish. Next to each other, they
create a hard, jagged transition from
roof to sky. But if you render the scene
at four times the resolution, that one
orange roof pixel becomes four pixels.
Some of those pixels are sky-coloured
and some are roof-coloured. If we take
the average of all four values, we get
something in between. Do that to the
whole scene and the transitions
become softer.
That’s the gist, at least, and while it
looks very good, supersampling is
computationally expensive.
Multisampling(MSAA)
More efficient thansupersampling,but
still demanding. Thisisthestandard,
baseline option in oldergamesCoverage Sampling(CSAA)
Nvidia’s more efficientversionofMSAA.Custom-filter(CFAA)
AMD’s more efficientversionofMSAA.Fast Approximate(FXAA)
Rather than analysingthe3Dmodels(ie
MSAA, which looksatpixelsonthe
edges of polygons),FXAAisapost-
processing filter, meaningitappliesto
the whole scene afterithasbeen
rendered, and it’s veryefficient.Italso
catches edges insidetextureswhich
MSAA misses. Thisisthedefaultin
many modern gamesbecauseithas
very little overhead.Morphological(MLAA)
Available with AMDcards,MLAAalso
skips the renderingstageand
processes the frame,seekingout
aliasing and smoothingit.AsNicholas
Vining explains, “Morphological
anti-aliasing looksatthemorphologyof
the jaggies on the edges.Foreachsetof
jaggies, it computesawayofremoving
the aliasing which ispleasingtotheeye.
It does this by breakingdownedges
and jaggies into littlesetsof
morphological operators,likeTetris
blocks, and then usesaspecialtypeof
blending for each Tetrisblock.”Enhanced Subpixel
Morphological (SMAA)
Another post-processing method,
described as combining MLAA with
MSAA and SSAA strategies. You can
apply it with SweetFX, and many
modern games natively support this.Temporal (TAA or TXAA)
TXAA was initially supported on Nvidia’s
Kepler and later GPUs, but more
general forms of temporal anti-aliasing
are now available and are typically just
labelled TAA. TAA compares the
previous frame with the current frame
to look for edges and help remove
jaggies. This is done through a variety of
filters and can help reduce the ‘crawling’
motion on edges, which looks a bit like
marching ants. It cannot, however,
remove actual ants from inside your
display. You should probably just throw
that display out.Multi-Frame (MFAA)
Introduced with Nvidia’s Maxwell GPUs.
Whereas MSAA samples in set
patterns, MFAA allows for
programmable sample patterns.Deep Learning Super-
Sampling (DLSS)
Nvidia’s latest, available on certain
games using new GeForce RTX cards.
According to Nvidia, “DLSS leverages a
deep neural network to extract
multidimensional features of the
rendered scene and intelligently
combine details from multiple frames to
construct a high-quality final image.
DLSS uses fewer input samples than
traditional techniques such as TAA,
while avoiding the algorithmic
difficulties such techniques face with
transparency and other elements.”
In other words, it’s better and more
efficient at doing the things Temporal
AA does, or at least it’s supposed to
look better once it has been properly
trained for a specific game.Anti-aliasing settings almost always include a series of values:
2x, 4x, 8x, and so on. The numbers refer to the number of
colour samples being taken, and in general, the higher the
number, the more accurate (and computationally expensive)
the anti-aliasing will be.
Then there’s the special case of the ‘Q’. CSAA attempts to
achieve a quality better than or equal to MSAA with fewer
colour samples, so 8xCSAA actually only takes four colour
samples. The other four are coverage samples. 8QxCSAA,
however, bumps the number of colour samples back up to
eight for increased accuracy. You’ll rarely encounter CSAA
these days, so let’s call that a fun fact.No AA 32xCSAA WHATdOTHE NuMBERSMEAN?
ANTI-AlIASINg