pamstretch
[-xscale=X]
[-yscale=Y]
[-blackedge]
[-dropedge]
N
[infile]

You can use the minimum unique abbreviation of the options. You can use
two hyphens instead of one. You can separate an option name from its value
with white space instead of an equals sign.

pamstretch scales up pictures by integer values, either vertically, horizontally,
or both.
pamstretch differs from
pnmscale and
pnmenlarge in that when it inserts the additional rows and columns, instead of
making the new row or column a copy of its neighbor,
pamstretch makes the new row or column an interpolation between its neighbors. In some
images, this produces better looking output.

To scale up to non-integer pixel sizes, e.g. 2.5, try
pamstretch-gen(1)
instead.

Options let you select alternative methods of dealing with the
right/bottom edges of the picture. Since the interpolation is done
between the top-left corners of the scaled-up pixels, it’s not obvious
what to do with the right/bottom edges. The default behaviour is to
scale those up without interpolation (more precisely, the right edge
is only interpolated vertically, and the bottom edge is only
interpolated horizontally), but there are two other possibilities,
selected by the
blackedge and
dropedge options.

The
N parameter is the scale factor. It is valid only if you
don’t specify
-xscale or
-yscale. In that case,
pamstretch scales in both dimensions and by the scale factor
N.

This is the horizontal scale factor. If you don’t specify this, but do
specify a vertical scale factor, the horizontal scale factor is 1.

-yscale=Y

This is the vertical scale factor. If you don’t specify this, but do
specify a horizontal scale factor, the vertical scale factor is 1.

-blackedge

interpolate to black at right/bottom edges.

-dropedge

drop one (source) pixel at right/bottom edges. This is arguably more
logical than the default behaviour, but it means producing output
which is a slightly odd size.