Convert an AVS X Image to PAM with avstopam

You will finish with a Netpbm image in PAM format produced from a Stardent AVS X image, plus a check that the output has the dimensions and tuple type you expected. The examples use avstopam from Netpbm package version 2:11.05.02-1.1build1, installed on this machine.

Allow about ten minutes. You need a readable AVS X file, a writable working directory and the Netpbm utilities. You do not need root access for conversion. Keep the original AVS file until the PAM output has been inspected.

1. Check the installed command

Confirm which executable will run and record the package version. These are ordinary read-only commands:

$ command -v avstopam
/usr/bin/avstopam
$ dpkg-query -W -f='${Package} ${Version}\n' netpbm
netpbm 2:11.05.02-1.1build1

The installed manual describes avstopam as a converter from an AVS X image to a Netpbm image. Its only positional argument is an optional input file. There are no avstopam-specific command-line options; it also accepts options common to libnetpbm programs.

Checkpoint: if command -v prints nothing, stop here and install Netpbm through your normal package-management process. Do not solve a missing executable by copying a binary from an untrusted location.

2. Convert a named AVS file

Give the AVS file as the positional argument and redirect standard output to a new destination:

$ avstopam /path/to/image.avs > image.pam

The input file is read by avstopam. The output is always written to standard output, so the shell redirection creates image.pam. A successful command normally prints no progress message. Check the exit status and the resulting file:

$ printf 'exit status: %s\n' "$?"
exit status: 0
$ test -s image.pam && echo 'PAM output is non-empty'
PAM output is non-empty

Do not assume that a file exists merely because the redirection created it. The shell opens the destination before starting the converter, so a failed conversion can still leave an empty or partial file.

3. Protect an existing output

$ avstopam /path/to/image.avs > image.pam.new
$ status=$?
$ if [ "$status" -eq 0 ] && test -s image.pam.new; then
>     mv image.pam.new image.pam
>     echo 'replacement installed'
> else
>     printf 'conversion failed, status %s; old image.pam was kept\n' "$status"
> fi

The mv runs only after a successful conversion and a non-empty output check. If the conversion fails, inspect the diagnostic and remove the incomplete image.pam.new when you are ready. That cleanup is optional. There is no state change to undo in avstopam itself; the important recovery is retaining the old destination.

4. Use standard input and standard output in a pipeline

Omit the input argument to make avstopam read standard input. This is useful when another tool produces an AVS stream:

$ generate-avs-image | avstopam > image.pam

The command at the left is a placeholder for a real AVS-producing program. Replace it with a trusted local command and check its exit status separately if the pipeline matters. With a shell that supports pipefail, this catches failure in either stage:

$ set -o pipefail
$ generate-avs-image | avstopam > image.pam
$ printf 'pipeline status: %s\n' "$?"
pipeline status: 0

For a file that you already have, the equivalent explicit stdin form is:

$ avstopam < /path/to/image.avs > image.pam

Do not confuse an empty input stream with a valid empty image. On this installation, running avstopam with no input produces the diagnostic Unexpected end of input file and exits with status 1.

5. Verify the PAM result

Use a Netpbm inspection tool rather than reading binary pixel data in a text editor. pamfile reports the dimensions, depth, maximum value and tuple type:

$ pamfile image.pam
image.pam: PAM, 2 by 1 by 4 maxval 255
    Tuple type: RGB_ALPHA

Your values will depend on the AVS input. Check that the reported width and height match the source, and that the depth and tuple type are suitable for the next program. In a real conversion, the exact line can vary with the image. A non-zero status or an error from pamfile means the output is not ready to hand to another image tool.

For a small smoke test, the installed pamtoavs command can create an AVS file from a Netpbm image, allowing a local round trip:

$ pamtoavs source.ppm > sample.avs
$ avstopam sample.avs > round-trip.pam
$ pamfile round-trip.pam
round-trip.pam: PAM, 2 by 1 by 4 maxval 255
    Tuple type: RGB_ALPHA

This tests the converter path and your output checks, not the fidelity of every possible AVS producer. The AVS file is an intermediate binary file, so keep it out of a text editor and do not infer its validity from a filename alone.

6. Diagnose the common failures

If the command cannot open the input, inspect the path and read permission without modifying the file:

$ ls -l /path/to/image.avs
$ test -r /path/to/image.avs && echo readable

If the input is empty or truncated, avstopam can report an unexpected end of input and return a failure status. Restore the AVS file from its source or backup, then rerun the conversion to a new temporary destination. Do not overwrite a known-good PAM while diagnosing the source.

If pamfile reports unexpected dimensions or a different tuple type, first check that you converted the intended AVS file and that a producer did not generate a different image. avstopam has no option for choosing output dimensions or resizing the image. Perform resizing or format conversion with a separate, appropriate Netpbm tool after the PAM result has passed inspection.

Elevated privileges are not normally needed. Do not use sudo to compensate for a bad path or malformed image. Use it only where your system permissions genuinely require access to a protected input or output directory, and prefer copying the file to a permitted working directory when policy allows.