lispmtopgm - convert a Lisp Machine bitmap file into pgm format
Reads a Lisp Machine bitmap as input. Produces a portable graymap as output.
This is the file format written by the tv:write-bit-array-file function on TI Explorer and Symbolics lisp machines.
Multi-plane bitmaps on lisp machines are color; but the lispm image file format does not include a color map, so we must treat it as a graymap instead. This is unfortunate.
The Lispm bitmap file format is a bit quirky; Usually the image in the file has its width rounded up to the next higher multiple of 32, but not always. If the width is not a multiple of 32, we don’t deal with it properly, but because of the Lispm microcode, such arrays are probably not image data anyway.
Also, the lispm code for saving bitmaps has a bug, in that if you are writing a bitmap which is not mod32 across, the file may be up to 7 bits too short! They round down instead of up, and we don’t handle this bug gracefully.
Copyright (C) 1991 by Jamie Zawinski and Jef Poskanzer.