Here are the data structures with brief descriptions:

filter	Struct representing a 1D FIR filter
image	Struct representing an image
penstruct	Pen drawing object
pentrans	Coordinate transformation matrix
programparams	Struct of program parameters
sinterpentry	Data for interpolating with a contour stencil
sinterpstruct	Data for interpolating with a contour stencil set
ssetstruct	A contour stencil set $\Sigma$
stencilentry	A single contour stencil $\mathcal{S}$
stencilqvec	Quantized vector
stencilsetcell	A cell in a contour stencil, $\Omega_k \subset \mathbb{R}^2$