PPMTOACAD

NAME

      ppmtoacad - convert portable pixmap to AutoCAD database or slide

SYNOPSIS

      ppmtoacad [-dxb] [-poly] [-background colour] [-white] [-aspect ratio]
                [-8] [ppmfile]

DESCRIPTION

      Reads a portable pixmap as input.   Produces  an  AutoCAD(Reg.)  slide
      file  or  binary database import (.dxb) file as output.  If no ppmfile
      is specified, input is read from standard input.

OPTIONS

      -dxb An AutoCAD binary database import (.dxb) file is  written.   This
           file  is  read  with  the DXBIN command and, once loaded, becomes
           part of the AutoCAD geometrical database and can  be  viewed  and
           edited  like any other object.  Each sequence of identical pixels
           becomes a separate object in the database;  this  can  result  in
           very  large AutoCAD drawing files.  However, if you want to trace
           over a bitmap, it lets you zoom and pan around the bitmap as  you
           wish.
      -poly
           If the -dxb option is not specified, the output of  ppmtoacad  is
           an   AutoCAD   slide  file.   Normally  each  row  of  pixels  is
           represented by an AutoCAD line entity.  If -poly is selected, the
           pixels  are  rendered as filled polygons.  If the slide is viewed
           on a display with higher resolution than the source pixmap,  this
           will  cause the pixels to expand instead of appearing as discrete
           lines against the screen background  colour.   Regrettably,  this
           representation  yields  slide  files which occupy more disc space
           and take longer to display.
      -background colour
           Most AutoCAD  display  drivers  can  be  configured  to  use  any
           available  colour  as the screen background.  Some users perfer a
           black screen background,  others  white,  while  splinter  groups
           advocate  burnt ocher, tawny puce, and shocking grey.  Discarding
           pixels whose closest AutoCAD colour representation  is  equal  to
           the  background  colour  can substantially reduce the size of the
           AutoCAD database or slide file needed to represent a bitmap.   If
           no  -background colour is specified, the screen background colour
           is assumed to  be  black.   Any  AutoCAD  colour  number  may  be
           specified as the screen background; colour numbers are assumed to
           specify the hues defined  in  the  standard  AutoCAD  256  colour
           palette.
      -white
           Since many AutoCAD users choose a white screen  background,  this
           option   is  provided  as  a  short-cut.   Specifying  -white  is
           identical in effect to -background 7.
      -aspect ratio
           If the source pixmap had non-square  pixels,  the  ratio  of  the
           pixel  width  to  pixel height should be specified as ratio.  The
           resulting slide or .dxb file will be corrected so that pixels  on
           the  AutoCAD  screen  will be square.  For example, to correct an
           image made for a 320x200 VGA/MCGA screen, specify -aspect 0.8333.
      -8   Restricts the colours in the output file to the 8 RGB shades.
      All flags can be abbreviated to their shortest unique prefix.

BUGS

      AutoCAD has a fixed palette of 256 colours, distributed along the hue,
      lightness,  and  saturation  axes.  Pixmaps which contain many nearly-
      identical colours, or colours not closely  approximated  by  AutoCAD's
      palette, may be poorly rendered.
      ppmtoacad works best if the system displaying its output supports  the
      full  256 colour AutoCAD palette.  Monochrome, 8 colour, and 16 colour
      configurations will produce less than optimal results.
      When creating a .dxb file or a  slide  file  with  the  -poly  option,
      ppmtoacad  finds both vertical and horizontal runs of identical pixels
      and consolidates them into rectangular regions to reduce the  size  of
      the  output  file.   This  is effective for images with large areas of
      constant colour but it's no  substitute  for  true  raster  to  vector
      conversion.   In  particular, thin diagonal lines are not optimised at
      all by this process.
      Output files can be huge.

SEE ALSO

      AutoCAD  Reference  Manual:  Slide  File  Format  and  Binary  Drawing
      Interchange (DXB) Files, ppm(5)

AUTHOR

           John Walker
           Autodesk SA
           Avenue des Champs-Montants 14b
           CH-2074 MARIN
           Suisse/Schweiz/Svizzera/Svizra/Switzerland
           Usenet:  kelvin@Autodesk.com
           Fax:     038/33 88 15
           Voice:   038/33 76 33
      Permission to use, copy, modify, and distribute this software and  its
      documentation  for  any  purpose  and  without  fee is hereby granted,
      without any conditions or restrictions.   This  software  is  provided
      ``as is'' without express or implied warranty.
      AutoCAD and Autodesk are registered trademarks of Autodesk, Inc.