Convert SRF Images to PAM Safely with srftopam

SRF is obscure enough that srftopam may be the only tool on your machine that still reads it. This guide converts an SRF image file into a PAM image stream with srftopam, saves it without damaging an existing result, and verifies the dimensions and tuple type. Allow about ten minutes if the SRF file is already on disk. You need the Netpbm package and a shell; the examples use Netpbm 11.5.2, installed here as package version 2:11.05.02-1.1build1.

srftopam reads one SRF input from a named file or standard input. It always writes PAM images to standard output. A single SRF file can therefore produce a multi-image PAM stream, so do not assume that one output file means one image.

1. Check the installed command

Confirm that the executable comes from the expected package before building a script around it:

$ command -v srftopam
/usr/bin/srftopam
$ srftopam -verbose < /dev/null
srftopam: short srf header

The second command deliberately feeds invalid input. It should fail with a non-zero status and report a short SRF header. That is a useful check that the command is running and that errors are going to standard error, not being mixed into the PAM stream. The installed binary also reports its Netpbm library version when -verbose is used, although it only reaches that point for input it can inspect.

Checkpoint: a real input must be readable, and command -v should show the Netpbm executable you intend to use. These conversion commands normally need no elevated privileges.

2. Convert an SRF file to PAM

Choose an output name that does not already contain useful data. The output redirection is performed by the shell before srftopam starts, so a plain > will truncate an existing destination even if conversion later fails.

$ srftopam /path/to/input.srf > /path/to/output.pam

SRF data is read from /path/to/input.srf; PAM data is written to /path/to/output.pam. There is normally no progress output. A successful exit status is necessary, but it does not prove that you supplied the intended file or that every image in the stream is suitable for the next tool.

For a new output name, check both the status and the file:

$ test -s /path/to/output.pam
$ printf 'conversion status: %s\n' "$?"
conversion status: 0
$ pamfile /path/to/output.pam
/path/to/output.pam:  PAM, 2 by 1 by 4 maxval 255
    Tuple type: RGB_ALPHA

Your dimensions and tuple type will vary. pamfile is a separate Netpbm utility, not part of srftopam, and its wording may differ slightly between releases. The useful checks are a non-empty output and the expected PAM metadata.

3. Use standard input in a pipeline

The input filename is optional because the manual defines standard input as the default. This makes the converter suitable for a pipeline that has already selected or downloaded the SRF data:

$ cat /path/to/input.srf | srftopam > /path/to/output.pam

For a simple file, naming the input is easier to audit. Use a pipeline when the upstream command is meaningful, and make its failure visible in scripts. In Bash, set -o pipefail causes the pipeline to fail if either side fails:

$ set -o pipefail
$ producer-command > /tmp/input.srf && srftopam /tmp/input.srf > /tmp/output.pam
$ status=$?
$ printf 'pipeline status: %s\n' "$status"
pipeline status: 0

Replace producer-command with a command that actually creates the SRF file. The example keeps temporary data under /tmp; use a private working directory if the input is sensitive.

4. Protect an existing output

Do not overwrite a valuable PAM file while testing a new conversion. Write to a temporary name in the same directory, inspect it, then replace the old file only after the checks pass:

$ srftopam /path/to/input.srf > /path/to/output.pam.new
$ pamfile /path/to/output.pam.new
/path/to/output.pam.new:  PAM, 2 by 1 by 4 maxval 255
    Tuple type: RGB_ALPHA
$ mv /path/to/output.pam.new /path/to/output.pam

mv changes the directory entry, so this final step is the point at which the old output is replaced. If conversion or inspection fails, leave the original alone and remove only the incomplete .new file after checking its path. Removal is irreversible. If you must preserve the old result before replacement, copy it first:

$ cp --preserve=all /path/to/output.pam /path/to/output.pam.bak

The backup is recovery material, not a substitute for checking the new PAM. Delete it only when the replacement has been opened or processed successfully.

5. Understand the available options

The command-specific option is -verbose. It requests informational messages about the input and conversion process. Keep those messages on standard error when capturing standard output as PAM:

$ srftopam -verbose /path/to/input.srf > /path/to/output.pam
$ pamfile /path/to/output.pam

Netpbm's common options include -quiet, which is useful when a script must suppress informational messages. Neither option changes the image data. The input file is not modified by srftopam, and there is no resize or output-file option: shell redirection controls the destination.

6. Diagnose a failed conversion

A message such as short srf header means the input did not contain enough SRF header data. Check the path, size and read permission without changing the file:

$ ls -l /path/to/input.srf
$ test -r /path/to/input.srf && echo readable
$ wc -c < /path/to/input.srf

If the input is unexpectedly empty or small, recover the original SRF from its source rather than trying to repair it with this converter. If the output is empty or incomplete, keep the old output, inspect the diagnostic on standard error, and rerun to a fresh .new name. Do not run as root to bypass a permission problem unless the file owner and access policy have been checked first.

Because the output can contain several PAM images, a downstream program may need to support a PAM image stream or process images one at a time. A single pamfile report is useful evidence about the stream, but it is not a visual check. Keep the SRF input until the converted images have been reviewed or consumed successfully.

Done means