Convert a Small SVG to PAM with svgtopam

You will convert a deliberately simple SVG path into a PAM image, inspect the result, and recognise when the input is outside svgtopam's very small supported subset. Allow about fifteen minutes, including time to check the output. The examples use Netpbm 11.5.2, installed here as package version netpbm 2:11.05.02-1.1build1.

This is not a general SVG renderer. The installed manual says that svgtopam understands only <path> elements using the M, L and z path commands, with whole-number arguments. That makes it useful for small test files and output from pamtosvg, but a poor choice for arbitrary SVG from a design tool or a web page.

1. Check the installed command

Start with ordinary, read-only checks. No elevated privileges are needed, and using sudo would not make unsupported SVG features work.

$ command -v svgtopam
/usr/bin/svgtopam
$ svgtopam --version
svgtopam: Using libnetpbm from Netpbm Version: Netpbm 11.5.2

The version output includes build details after the first line. Your package may be different, so keep the local manual and command output together when diagnosing a failure.

2. Prepare an SVG the parser can draw

The example below describes a red square. The style attribute is intentional: this implementation reads the fill colour from it. The path moves to the top-left corner, draws three lines, and closes with z. All coordinates are whole numbers.

<?xml version="1.0"?>
<svg width="160" height="100" xmlns="http://www.w3.org/2000/svg">
  <path style="fill:#d40000" d="M10 10 L150 10 L150 90 L10 90 z" />
</svg>

Save that as square.svg in a working directory. This changes only the new file. If you are copying an existing SVG, preserve the original and work on a copy so that failed experiments are easy to abandon.

$ mkdir -p "$HOME/tmp/svgtopam-example"
$ cd "$HOME/tmp/svgtopam-example"
$ cp /path/to/square.svg .

The output dimensions come from the SVG's width and height attributes. They are not options to svgtopam, and the command does not offer a resize switch.

3. Convert to PAM without overwriting an image

Pass the SVG file as the optional positional argument and redirect standard output to a new destination. Use a name that does not already contain useful data.

$ svgtopam square.svg > square.pam
$ printf 'exit status: %s\n' "$?"
exit status: 0

A successful exit status means the program completed its parse and drawing operation. The image itself is binary PAM data, so normal output belongs in a file. Do not paste it into a terminal or redirect it over the source SVG.

$ cp --preserve=all square.pam square.pam.bak
$ svgtopam square.svg > square.pam.new
$ test -s square.pam.new && mv square.pam.new square.pam

If conversion fails, remove only the incomplete square.pam.new after checking the error. The backup and the previous PAM file remain available. The final mv is the state-changing step; it needs no root access when the directory belongs to you.

4. Verify the PAM header and dimensions

Use Netpbm's pamfile when it is installed. This inspects the file without changing it.

$ pamfile square.pam
square.pam: PAM, 160 by 100 by 3 maxval 255
    Tuple type: RGB

The wording may vary slightly between Netpbm builds. Check for a PAM image, dimensions of 160 by 100, depth 3 and maxval 255. The example's red square should occupy the path's area, with the rest of the canvas represented according to the installed renderer's output.

If pamfile is unavailable, check the file type and the first part of its header without opening the binary image in an editor:

$ file square.pam
$ od -An -c -N 80 square.pam

The header should begin with P7 and include WIDTH 160, HEIGHT 100, DEPTH 3 and MAXVAL 255. Treat a zero-length file or a missing header as a failed conversion, even if a shell pipeline made the command look tidy.

5. See what -trace is doing

When a path is accepted but the drawing is not what you expect, add -trace. It writes drawing messages to standard error, leaving PAM data on standard output.

$ svgtopam -trace square.svg > square-traced.pam
svgtopam: Drawing path 'M10 10 L150 10 L150 90 L10 90 z' with fill color (212, 0, 0)
svgtopam: Moving to (10, 10)
svgtopam: Lining to (150, 10)
svgtopam: Lining to (150, 90)
svgtopam: Lining to (10, 90)
svgtopam: Closing.

The exact colour formatting and diagnostic wording belong to the installed build. The useful signals are that the path was found, its fill was parsed, and each move or line was processed. If you need a quiet conversion, omit -trace or use the common -quiet option documented by Netpbm.

6. Diagnose unsupported SVG

Most failures are not permissions problems. They are a mismatch between modern SVG and this intentionally narrow parser. Text, circles, rectangles, curves, fractional coordinates, transforms and many other SVG features are not described as supported by the manual. A normal browser may display such a file while svgtopam rejects it or produces no useful image.

Reduce a failing file to one path with integer coordinates and an inline fill style. For example, replace a rectangle element with an equivalent path:

<path style="fill:#336699" d="M0 0 L80 0 L80 60 L0 60 z" />

Then rerun with -trace and verify the resulting PAM file. If the source depends on curves or typography, use a full SVG renderer or export through an image tool that supports those features. Do not keep changing shell flags: this command has one drawing option, -trace, not a hidden compatibility mode.

An XML parse error usually means the input is malformed. A message about a missing attribute or an unsupported path construct means the file reached the program but did not match its expected subset. Keep the original SVG, save each trial output under a new name, and compare headers before inspecting pixels.