Using multi sampling we estimate the colour of a pixel by sampling the scene with multiple rays through that pixel and average the colours. This provides a simple means of anti-aliasing.
I have implemented two sampling methods, random and stratified sampling.
With random sampling the points suffer from bunching or areas of emptiness within the unit square and may give an inaccurate estimate to the average pixel colour.
Stratified sampling provides a more uniform samples, by evenly dividing the unit square into and n by n sub squares and each sample generate is inside one of these sub squares. The simplest form is called regular sampling, which places a sample at the centre of each of the sub squares. With jittered sampling the samples are random, but still within each sub square.
Below shows the 16 samples within a unit square produced with each method.