When making a plot where there are a relatively small number of pixels per data point, "pixelation" noise can be significant. By checking the "Antialias" box, you can correct for this to some extent. The program breaks each pixel up into 4 sub-pixels, each with 25% of the intensity, and apportions the intensity accordingly. This results in cleaner looking plots, but also takes approximately 4 times as long to calculate, so it should only be turned on when you are satisfied that you have the plot range, etc., set the way you want.