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® 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.
10 October 1991 ppmtoacad(1)