ExtendBorder
Returns a pixmap with its border (outermost rectangle of pixels) extended outwards.
Syntax

ExtendBorder(pm, w[, h])

pm
is a pixmap 
w
andh
are nonnegative integers

Description
ExtendBorder(pm, w, h)
returns the pixmap obtained from pm
by extending its border (the outermost rectangle of pixels, that is, the union of the top row, bottom row, leftmost column, and rightmost column) outwards. The four corner pixels are made into rectangles, the remaining top and bottom pixels are copied vertically h
pixels on each side, and the remaining left and right pixels are copied horizontally w
pixels on each side.
If omitted, h
defaults to w
.
Examples
ExtendBorder(ExampleData("harvestman"), 50)