Chris Moulding's cs684 homework page

Homework 3

This table has some examples of sampling techniques. Some use different filters; some use different sampling strategies.
key:
box filter: the pixel is divided into a regular N x N grid. Samples will then be taken from each of the cells that form the grid. Takes a while, but is thorough.

N-rooks filter: same as box filter except that only N cells will actually be sampled. Each row of the grid has only one sample; likewise each column only has one sample. When the below images indicate X samples per pixel, N-rooks actually only samples sqrt(X) times--there are,however, X cells in the grid. Faster than regular box filter, but is less thorough.

jitter: after a stratification and cell selection the cells need to be sampled. Typically a sample is taken at the middle of each cell. Jittering randomly moves the sample point around, within the cell along both axis. Shown to converge to the "correct" image faster than no-jitter strategies.

min-max: instead of averaging all of the samples for a final sample value for the pixel, find the minimum value and maximum value of all of the samples and then average only those two. Kills all signals above some frequency threshold. This is the most blind and dumb method for sampling, but has the best (fastest) convergence for this test pattern.

49 samples/pixel box filter

49 samples/pixel N-rooks filter

1 samples/pixel box filter jitter

16 samples/pixel box filter jitter

25 samples/pixel box filter jitter

49 samples/pixel box filter jitter

1 samples/pixel n-rooks filter jitter

16 samples/pixel n-rooks filter jitter

25 samples/pixel n-rooks filter jitter

49 samples/pixel n-rooks filter jitter

1 samples/pixel n-rooks filter jitter & min-max

16 samples/pixel n-rooks filter jitter & min-max

25 samples/pixel n-rooks filter jitter & min-max

49 samples/pixel n-rooks filter jitter & min-max

1 samples/pixel box filter jitter & min-max

16 samples/pixel box filter jitter & min-max

25 samples/pixel box filter jitter & min-max

49 samples/pixel box filter jitter & min-max