The pdf
and png terminal drivers have been supplemented (or perhaps replaced, depending on the details of how your version of gnuplot was compiled) by higher quality versions that use the cairo graphics library.
As the emphasis in this chapter is on achieving the highest possible quality for publication in electronic documents or on paper, we are devoting the first recipe to showing you how to select and use gnuplot's new high-quality terminal drivers.
In the previous figure, we can clearly see the increase in quality when using the new pngcairo terminal driver rather than the older, libgd-based terminal. Text and anti-aliasing is handled better, and the drawing of curves in plots is vastly improved. The curve in the older version is clearly more jagged, while the cairo library smoothly interpolates the curve between sample points.