Convert Netpbm Images to Targa with ppmtotga

ppmtotga turns a Netpbm image into a Truevision Targa file, and the first thing worth knowing is that it is not really its own program any more. On a current Netpbm install it is the old name for pamtotga, so the real workflow is: recognise the alias, pick an output mode on purpose, and verify the result. Allow about ten minutes for one conversion and a basic check.

1. Check the installed command

Install the distribution's netpbm package first if you have not already. On the machine this guide was checked against, Debian's Netpbm package is version 2:11.05.02-1.1build1, providing Netpbm 11.5.2, and the installed ppmtotga is a symbolic link to pamtotga. The old manual page says the name was replaced in Netpbm 10.6, so new scripts should use pamtotga; keep ppmtotga only when maintaining an older command line or documenting a legacy workflow.

$ command -v ppmtotga
/usr/bin/ppmtotga
$ readlink -f "$(command -v ppmtotga)"
/usr/bin/pamtotga
$ ppmtotga --version
ppmtotga: Using libnetpbm from Netpbm Version: Netpbm 11.5.2

The version command also prints build details on this installation. Its standard output is still the Targa image itself, so send it to a file rather than letting it spew into your terminal.

2. Inspect the input before converting

pamtotga accepts PBM, PGM, PPM and PAM input. PAM can also describe black-and-white, greyscale, RGB and RGB with an alpha channel. Use pamfile to check the input without changing it:

$ pamfile /path/to/input.ppm
/path/to/input.ppm: PPM raw, 320 by 200 by 255
$ test -r /path/to/input.ppm && echo readable
readable

The exact wording from pamfile varies by Netpbm release. Confirm the reported dimensions and format match what you expect. Readable files in your own working directory need no elevated privileges; do not reach for sudo just because the output format is old or binary.

3. Make a conservative conversion

Pick a new destination and use the modern command name for new work. With no image-type option, pamtotga chooses the most constrained compatible Targa type: monochrome before colour-mapped before full RGB.

$ pamtotga /path/to/input.ppm > /path/to/output.tga
$ test -s /path/to/output.tga && echo "Targa output is non-empty"
Targa output is non-empty
$ file /path/to/output.tga
/path/to/output.tga: Targa image data, 320 x 200, RGB

file is a useful first check, but its description comes from the local file utility and can differ. A successful exit status, a non-empty destination and plausible dimensions together give a practical conversion check. Open the Targa with a trusted viewer if visual correctness matters.

4. Select the Targa representation

Use -rgb when you need an unmapped 24-bit colour Targa and want to skip palette selection entirely:

$ pamtotga -rgb /path/to/input.ppm > /path/to/output-rgb.tga

• -cmap requests a palette, for input with no more than 256 distinct colours. It does not accept transparency input.
• -cmap16 is the 16-bit palette variant, added in Netpbm 10.85.
• -mono requests an 8-bit monochrome Targa, for PBM, PGM or compatible PAM input.

Choose at most one of -mono, -cmap and -rgb. If a script needs a predictable result, spell the option out and keep the input constraints explicit.

For an RGBA-style PAM image, leave the input as RGB with transparency and skip the palette options. The output gets a fourth byte per pixel and a 32-bit Targa header. The manual warns that software support for Targa transparency is limited, so check the receiving application before making this your interchange format.

5. Handle compression and the image name

Targa run-length encoding is on by default. Some readers cannot handle it, so use -norle for an uncompressed raster:

$ pamtotga -norle /path/to/input.ppm > /path/to/output-uncompressed.tga
$ file /path/to/output-uncompressed.tga

Use -name=scan-2026 to set the image ID stored in the Targa header. Without it, the program uses the input file name up to its first period, or omits the ID entirely when reading standard input. The value is truncated as needed to fit Targa's limits. -verbose reports conversion details; it does not replace checking the output.

6. Protect an existing output

$ pamtotga -rgb /path/to/input.ppm > /path/to/output.tga.new
$ test -s /path/to/output.tga.new
$ file /path/to/output.tga.new
/path/to/output.tga.new: Targa image data, 320 x 200, RGB
$ mv /path/to/output.tga.new /path/to/output.tga

7. Diagnose the likely failures

• Missing-input error. Usually the path is wrong or the file is not readable.
• Palette conversion fails. The input probably has more than 256 colours, or carries transparency.
• Monochrome conversion fails. It requires PBM, PGM or a compatible black-and-white or greyscale PAM.
• Another program rejects the Targa. Retry with -norle, -rgb or whatever representation that program documents, then inspect the result again.

Use man pamtotga for the installed option contract. The ppmtotga page is intentionally short because it documents the replacement, not a separate implementation. Nothing in this guide changes system configuration, and none of it normally needs root access.