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svg_strip_background.php

This utility script removes background rectangles that span the entire canvas of an SVG image.

Pathbuild/svg_strip_background.php
LanguagePHP
Lines29

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Overview​

This utility script removes background rectangles that span the entire canvas of an SVG image. Many design tools (Figma, Illustrator, etc.) export SVGs with a full-size background rectangle, which is usually unnecessary for web use and increases file size. This script identifies and removes such backgrounds by detecting <path> elements that draw a rectangle matching the SVG's width and height.

The script is particularly useful for icons and graphics that should have transparent backgrounds. It modifies SVG files in-place, preserving all other elements and attributes.

The detection is based on a specific path syntax (M-0 -0L{width} 0L{width} {height}L-0 {height}L0 -0Z) that creates a rectangle from corner to corner. This pattern is common in SVG exports that include background layers.

Key Functions/Variables​

Variables​

  • $svg_tag_regexp: Pattern to extract width and height from the <svg> tag: /<svg ([^<>]* )?width="(.+?)" ([^<>]* )?height="(.+?)"[^<>]*>/
  • $path_regexp: Dynamic pattern constructed using extracted width/height to match the background rectangle path. Looks for: M-0 -0L{width} 0L{width} {height}L-0 {height}L0 -0Z
  • $file_names: Array of SVG file paths from command-line arguments
  • $width and $height: Extracted from the <svg> tag to construct the background path pattern

Path Patterns​

The script looks for this specific path syntax (absolute coordinates):

M-0 -0L{width} 0L{width} {height}L-0 {height}L0 -0Z

There's also a commented-out alternative pattern for relative coordinates:

M0 0h{width}v{height}H0z

Input/Output​

Inputs​

  • SVG files: One or more SVG file paths as command-line arguments

Outputs​

  • Modified SVG files: Original files are overwritten with the background path removed (if found)

The script prints each filename as it processes it.

Background Removal Process​

  1. Read SVG file: Load entire file contents
  2. Extract dimensions: Use regex to find width="..." and height="..." in <svg> tag
  3. Construct path pattern: Build regex to match a path that draws a rectangle from (0,0) to (width, height)
  4. Match background path: Search for <path d="M-0 -0L{width} 0L{width} {height}L-0 {height}L0 -0Z"...>
  5. Remove matched path: Replace the entire <path> element with empty string
  6. Write back: Overwrite original file with modified SVG

Example​

Given an SVG with:

<svg width="100" height="50">
  <path d="M-0 -0L100 0L100 50L-0 50L0 -0Z" fill="#ffffff"/>
  <circle cx="50" cy="25" r="20" fill="#000000"/>
</svg>

After processing:

<svg width="100" height="50">
  <circle cx="50" cy="25" r="20" fill="#000000"/>
</svg>

The background rectangle is removed, leaving only the content.

Usage​

# Process one SVG
php svg_strip_background.php icon.svg

# Process multiple SVGs
php svg_strip_background.php icon1.svg icon2.svg icon3.svg

# Process all SVGs in a directory
php svg_strip_background.php icons/*.svg

Files are modified in-place, so make backups if needed.

Limitations​

  • Only detects background paths in the specific format M-0 -0L{width} 0L{width} {height}L-0 {height}L0 -0Z
  • Does not detect backgrounds that use <rect> elements
  • Does not detect backgrounds with different path syntaxes (though an alternative pattern is commented out)
  • Modifies files in-place with no backup
See Also