CMSC 435

Antialiasing

Aliasing

Visual artifactsjagged lines and edges

high frequencies appearing as lowsmall objects missedtexture distortions

strobing and poppingbackward movement

Rendering Process

Two basic stagessamplingreconstruction

Assuming discrete sampling

Sampling Theory

Shannon s sampling theory (1D):A band limited signal f(t) with cut off frequency wFmay be perfectly reconstructed from its samplesf(nT0) if 2 /T0 >= 2wF

wF == Nyquist limit

Alternatively:a signal can be reconstructed exactly fromsamples only if the highest frequency is less thanhalf the sampling rate

Sampling Schemes

Regular supersamplingJittered supersamplingAdaptive supersamplingStochastic sampling

Reconstruction

Reconstruction: recreate a continuoussignal from a set of samplesTasks of reconstruction filter

remove extraneous replicas of signalspectrum

pass the original signal base unchanged