Convert PPM Images to AutoCAD Slides or DXB Files

You will convert a PPM image into an AutoCAD slide file or a binary drawing interchange file that AutoCAD can import with DXBIN. The examples use the Netpbm ppmtoacad installed on this machine, package version 2:11.05.02-1.1build1. Allow about ten minutes if the PPM is ready and you only need a basic conversion.

You need a readable PPM file and enough free space for the output. The output can be unexpectedly large, particularly for a DXB file or a slide made with -poly. These commands normally need no elevated privileges. Do not use sudo unless file permissions genuinely require it.

1. Check the installed command

Confirm that the executable is the one you expect and record the package version:

$ command -v ppmtoacad
/usr/bin/ppmtoacad
$ dpkg-query -W -f='${Package} ${Version}\n' netpbm
netpbm 2:11.05.02-1.1build1
$ ppmtoacad -help
ppmtoacad: Use 'man ppmtoacad' for help.

The local manual describes the command as reading PPM from a named file or standard input. It writes an AutoCAD slide by default. The -dxb option selects a binary database import instead.

2. Create a slide from a PPM

Use shell redirection to choose the output filename. This example leaves the input untouched:

$ ppmtoacad /path/to/image.ppm > image.sld
$ printf 'exit status: %s\n' "$?"
exit status: 0
$ file image.sld
image.sld: data

A successful run can still produce a file identified only as generic data by file, because slide files are not necessarily recognised by that utility. The useful checks are a zero exit status, a non-empty destination and a sensible size. In AutoCAD, load the slide using the product's slide-viewing workflow.

The default background is AutoCAD colour number 0, normally black. Pixels whose nearest AutoCAD colour matches that background can be discarded, reducing output size. If your display uses a white background, use the documented shortcut:

$ ppmtoacad -white /path/to/image.ppm > image-white.sld
$ test -s image-white.sld && echo 'slide written'
slide written

-white has the same effect as -background 7. You can provide another palette number explicitly, for example -background 1. The number refers to AutoCAD's standard 256-colour palette, not to an RGB value.

3. Produce a DXB import instead

Choose -dxb when the destination workflow needs a binary drawing database import:

$ ppmtoacad -dxb /path/to/image.ppm > image.dxb
$ test -s image.dxb && echo 'DXB file written'
DXB file written

After import with AutoCAD's DXBIN command, the result becomes part of the drawing database and can be viewed or edited like other geometry. The converter represents runs of identical pixels as separate objects. That can make a DXB drawing very large, although it also makes zooming and tracing over a bitmap practical.

Keep the source PPM until the import has been checked. The command does not alter the input, but the redirection operator can truncate an existing destination before ppmtoacad starts.

4. Preserve an existing output safely

$ ppmtoacad -dxb /path/to/image.ppm > image.dxb.new
$ test -s image.dxb.new
$ mv image.dxb.new image.dxb

If conversion fails, the old image.dxb remains in place. Remove the incomplete temporary file with rm -- image.dxb.new after checking that it is the intended temporary file. If you have already replaced a file and need recovery, restore it from your normal backup. There is no general undo command for a shell redirection.

5. Match the image geometry

PPM normally describes square pixels. If the source uses non-square pixels, pass the ratio of pixel width to pixel height with -aspect. For a 320 by 200 VGA or MCGA image, the manual gives this example:

$ ppmtoacad -aspect 0.8333 /path/to/vga-image.ppm > vga-image.sld

This corrects the generated slide or DXB geometry so that the displayed pixels are square. It does not resize the PPM and it does not repair a wrong image width or height. Work out the ratio from the source format rather than guessing.

For a less colourful result, -8 restricts the output to eight RGB shades. This may be useful for a simple diagram, but it discards colour information. Test the result visually before using it as a tracing reference.

6. Use polygons only when they help

Without -dxb, each source row is normally represented by a line in the slide. Add -poly to render pixels as filled polygons:

$ ppmtoacad -poly /path/to/image.ppm > image-polygons.sld
$ test -s image-polygons.sld && echo 'polygon slide written'
polygon slide written

Polygons can make pixels expand on a higher-resolution display instead of appearing as isolated lines. The trade-off is a larger file and slower display. Use this option for a deliberate viewing reason, not as a general quality setting. The manual also warns that run consolidation is not true raster-to-vector conversion and does not optimise thin diagonal lines.

7. Diagnose a result that looks wrong

First check the input without changing it:

$ test -r /path/to/image.ppm && echo 'input is readable'
$ file /path/to/image.ppm

If the command reports a PPM parsing error, validate the image with another Netpbm reader such as pamfile if it is installed. If the AutoCAD image is too large, try the default slide mode, choose an appropriate background, or simplify the source. Large output is expected for detailed images, DXB mode and polygon slides.

If colours are poor, remember that AutoCAD has a fixed 256-colour palette. Images containing many nearly identical colours cannot all be represented accurately. An eight-colour display will also show less useful results than a display using the full AutoCAD palette. These are format limits, not evidence that the PPM was resized.

Options may be abbreviated to their shortest unique prefix, but full names are clearer in scripts. Keep them full when a command will be reviewed or reused. The command accepts standard Netpbm options such as -quiet; use them only when you have already confirmed that the conversion works.