e Netpbm used to have a maximum maxval of 255, which meant
that the largest convolution kernel <B>pnmconvol</B> could use was 11
by 11, <B>ppmshadow</B> includes a horrid, CPU-time-burning kludge
which, if a blur of greater than 11 is requested, performs an initial
convolution with an 11 x 11 kernel, then calls <B>pnmsmooth</B>
(which is itself a program that calls <b>pnmconvol</b> with a 3 x 3
kernel) as many times as the requested blur exceeds 11.  It's ugly,
but it gets the job done on those rare occasio